This PDF file contains the front matter associated with SPIE Proceedings Volume 8796, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Chemical laser propulsion (CLP) is accompanied by the release of chemical energy in the process of laser propulsion, which can improve laser propulsion performance. In this article the propulsion performance of POM propellant under the constraint of a cylindrical tube-type thruster in atmospheric and nitrogen environments, respectively, has been conducted experimentally. The results indicate that the ablation masses of a single pulse under two gas environments are close, but the momentum coupling coefficient C_m and specific impulse Isp in atmospheric environment are higher than that in nitrogen environment, which demonstrates an exothermic reaction occurred between the ablation product and the environment oxygen. To learn the mechanism of CLP the molecular spectra for ablation products of POM propellant in atmospheric and vacuum environments are measured and analyzed, respectively, and it reveals that the final product in a vacuum is CH₂O, while the final products are CO₂ and H₂O in the atmosphere. Then the chemical reaction, composition and chemical energy release have been confirmed in the atmospheric environment. By using Arrhenius finite rate chemical reaction model with the code Fluent the flow field evolution of ablation product was simulated numerically. The results show the intensity of chemical energy release is related to the contact and mixing degree of the ablation product and the oxygen in the atmosphere, mixing more fully, the chemical energy released more intensively.

The irradiation effects are studied, of solid-state laser on four kinds of plates (three of them are made of metal, the other, of composite), in experiments characterized by relatively large laser spot and the presence of surface flow. The thick iron samples, thin aluminum samples and thin carbon fiber/epoxy resin samples are subjected to air or N₂ surface flow, while the box-shaped samples, containing a thin aluminum plate irradiated by laser, are filled with water. It is found that, besides the common role in all four cases cooling the plate by convective heat transfer, the fluid plays other different roles in different case influencing the dynamic response of the plate. The roles of the fluid in each case are described either with analytical boundary conditions or with differential equations, which are then incorporated into computational models. Numerical simulations are carried out, with results compared with the experiment results to explain the irradiation effects.

The experiment of 1.06μm laser damage visible imaging system individually at the state of CW(continuous wave),repetitive frequency of 40KHz and 5KHz was carried out. The damage threshold corresponding to each state was measured. It was found that the threshold of repetitive frequency laser was lower than that of CW laser, and the threshold of 5KHz repetitive frequency laser was lower than that of 40KHz laser. With the method of finite element analysis, the temperature change and thermal-stress distribution of detector material induced by CW and repetitive frequency laser irradiation were simulated. By analyzing temperature peak effect and thermal-stress effect of repetitive frequency laser, the reason why repetitive frequency laser had better damage effect was properly explained. By comparing the temperature rise of material induced by laser of different repetitive frequency, the conclusion that laser of lower repetitive frequency had better damage effect was obtained.

In this paper, a coupled thermal-fluid-structure numerical model is presented to investigate interactive effects of supersonic airflow, high power laser and metallic target. The numerical model is validated by experiments recently carried out by Lawrence Livermore National Laboratory. The numerical simulation also verified some experimental observations, which show that the convective heat transfer effects of airflow and the aerodynamic pressure play important roles to the damage behavior of laser irradiated target. The convective heat transfer of airflow reduces the temperature of laser irradiated area therefore delays the time reaching damage. When a thin-walled metallic panel is heated up to a high temperature below the melting point, it is softened and the strength nearly vanishes, the aerodynamic pressure becomes a dominant factor that controls the damage pattern even when it is in a low magnitude. The effects of airflow velocity and laser power on the damage behavior of irradiated metallic target are investigated with the aid of the coupled thermal-fluid-structure numerical model, where critical irradiation times to reach the yield failure t _yield and melting failure t _yield are the main concern. Results show that, when the incidence laser power increases from 500 W/cm² to 5000 W/cm², significant drop in failure times are found as the incidence laser power increases. When the Mach number of airflow increases from 1.2 to 4.0 at a given incident laser power, a critical airflow velocity is found for the irradiation time to reach the yield strength and melting point, i.e., the maximum irradiation time to reach failure is found at the Mach 1.8~2.0. The competition of aerodynamic heating before the laser is switch on and airflow cooling after the target is heated up accounts for effects.

Numerical simulation and analysis of the temperature distributions in multilayers under laser irradiation have been reported. Using finite element method (FEM), we have developed 2D and 3D programs, and calculated the temperature distributions under irradiation of immovable or laterally movable laser beams. The simulated results show that the maximum temperature rise appears at where the most laser energy deposition is. The results also show that when the moving velocity of laser beam is not so fast, the maximum temperature rise would not descend much compared with immovable irradiation.

A threat to spacecraft in long-term low earth orbits is the high probability of impacts with small particles of man-made space debris in 1-cm to 10-cm size range. One possible solution for 1-10 cm size debris is to de-orbit the particles with a ground or space based laser. A modified torsional impulse balance system has been developed as a diagnostic tool to study fundamental laser ablative process on different material such as aluminum, titanium, magnesium and carbon fiber composite that are frequently used in spacecraft. Of particular interest is the force due to process of laser ablation as well as the impulse coupling coefficient. It can be concluded from the experimental result that for the experimental materials, with the increasing laser intensity, the coupling coefficient increase firstly and then decrease and it reaches the maximum at some value when the laser intensity varies around 10⁹ W/cm². And the experimental data compares well with the calculation result according to Phipps' scaling law. As we extend the previous research, it will provide a reference for the study in cleaning man-made space debris by laser.

Laser propulsion as a new concept propulsion technology, it is paid more and more extensive concern. Laser ablation micro thruster is one of the focus with its high specific impulse, wide dynamic range of impulse, small minimum impulse bit, low power etc, laser ablation micro thruster has wide application prospects on high-precision task of satellite attitudeadjustment, orbit maintain and networking formation control. Due to low thermal conduction, low ablation threshold, polymer material was easily ablated to generate thrust. A computational model of laser ablated polymer was established to simulated the micro-thruster working in vacuum environment. The polymer don’t have fixed fusion point, so build the ablation criterion based on threshold energy, which has observed in many experiments. Put forward the polymer ablation criterion in the numerical model, the target ablation phenomenon happens when inner deposited energy achieve the threshold value. Established the energy distribution equation to describes the ablation process of temperature rise, phase change and the influence of chemical exothermic process. When ablation phenomenon happened the ablation products would ejected, and the target gained recoil impulse from ejection process. According to energy distribution equations we can get the ejection energy, and then get the recoil momentum of target based on momentum conservation law. The propulsion properties of laser ablated polymer was studied through the numerical analysis model. Revealed the relationship between the propulsion capability and laser parameters. Analyzed influence of different propellants to propulsion performance. The numerical analysis model can reflect the propulsion capability of different polymer propellant, revealed the law of propulsion parameters in laser ablation process.

Both scanning laser irradiation mode and the static mode can cause damage to the materials with different thresholds. In this paper, a simple criterion is derived theoretically to equate the threshold of static irradiation with the scanning one for flat-top laser so that the two damage threshold at different scanning velocity can be compared. The results of numerical simulations are in good agreement with the criterion, and the preliminary experiments verify the criterion.

Ablaiton of solid target with high power energy can induce laser vapor plasma, which would impart reverse impulse to the target. The physical processes include target heating, melting, vaporization and formation of plasma plume. In this paper, we presented a new numerical model, which described target heating, melting and evaporation. Meanwhile, the ejection of material formed a plasma plume above the surface and expanded into the ambient vacuum. The formed plasma absorbed the laser energy passing through it. The heating of the target was described with a heat conduction equation, which led to the temperature distribution inside the target, as a function of time. When the temperature rises further, vaporization would appear. The vapor velocity and temperature at the surface were used as input for the boundary conditions of plasma plume, which was described with Navier–Stokes equations, for conservation of total vapor mass density, momentum and energy. We considered two dominant absorption mechanisms in the process of plasma shielding, which were electron–ion and electron–neutral inverse Bremsstrahlung. Based on above assumptions, the left laser energy because of plasma shielding was calculated. Results for an aluminum target with Gaussian profile laser pulse with duration of nanosecond were obtained, including the plasma plume temperature, ionization degree, densities of neutral, ions and electrons and laser absorption energy. Results showed that the energy absorption by plasma plume played an important role in the coupling of laser energy and target.

In laser thrusters, the reflectors of the focusing system work under high-intensity laser radiation. The material choice of the reflectors is quite important due to thermal load raised by laser absorption. Meanwhile the endurance of heavy thermal load should be attributed to the metallic reflectors with low laser energy absorption ratio. Based on two-dimension heat conduction equation and several approximations, this study investigates the melting time and thermal deformation characteristics for three kind of metallic materials that are of high heat specific heat, high conductivity and high melting point, and so are some alloys. Calculated through Finite Differential Method, the results show that, as for the twice reflecting focusing system, the thermal load is quite remarkable for the both reflectors and is more serious for the second one, while different materials present distinct thermal endurance performance. For the materials under study, the beryllium mirrors featuring higher specific heat could endure longer laser radiation and may prolong the work time. Moreover, if the reflecting mirror is required to work under high laser radiation for longer time, the aid of cooling system maybe indispensable.

The porous silicon (PS) has gained increasing attentions in fields of nanoenergetic materials because of its especial chemical properties and mesoporous structured property (a large specific surface area: ～600m2/g). In this paper, the patterned (PS) films were realized by lithography technique on the polished surface of monocrystal silicon substrates, and the PS nanoenergetic chips (nECs) were created by impregnating the nanoscale pores of PS with ammonium perchlorate under the ultrasonic wave. The combustion of PS nECs was ignited by single pulse laser and the selfsustained burning was recoded by an optical high-speed camera at 20,000 frames per second. Its combustion performance was enhanced by ultrasonic wave in fabrications. Experiment results shown that the radial burning and channel burning were typical stages in combustions of PS nECs. In addition, the igniting energy of pulse laser beams affected the burning properties of PS nECs: the combustion of PS nECs could translate from propellant burning to deflagration with increases of laser beams energy ranged from 0.134mJ to 425mJ. In this work, the diameter of the irradiated spot on the PS nECs was about 700μm.. A strong plume of flame was emitted from the surface of PS nECs and this indicated that the potential for PS nECs to be applied as microigniters matrix chips and microthrusters matrix chips.

Charged Coupled Devices (CCD) are widely used in military and security applications, such as airborne and ship based surveillance, satellite reconnaissance and so on. Homeland security requires effective means to negate these advanced overseeing systems. Researches show that CCD based EO systems can be significantly dazzled or even damaged by high-repetition rate pulsed lasers. Here, we report femto - second laser interaction with CCD camera, which is probable of great importance in future. Femto - second laser is quite fresh new lasers, which has unique characteristics, such as extremely short pulse width (1 fs = 10^-15 s), extremely high peak power (1 TW = 10¹²W), and especially its unique features when interacting with matters. Researches in femto second laser interaction with materials (metals, dielectrics) clearly indicate non-thermal effect dominates the process, which is of vast difference from that of long pulses interaction with matters. Firstly, the damage threshold test are performed with femto second laser acting on the CCD camera. An 800nm, 500μJ, 100fs laser pulse is used to irradiate interline CCD solid-state image sensor in the experiment. In order to focus laser energy onto tiny CCD active cells, an optical system of F/5.6 is used. A Sony production CCDs are chose as typical targets. The damage threshold is evaluated with multiple test data. Point damage, line damage and full array damage were observed when the irradiated pulse energy continuously increase during the experiment. The point damage threshold is found 151.2 mJ/cm².The line damage threshold is found 508.2 mJ/cm².The full-array damage threshold is found to be 5.91 J/cm². Although the phenomenon is almost the same as that of nano laser interaction with CCD, these damage thresholds are substantially lower than that of data obtained from nano second laser interaction with CCD. Then at the same time, the electric features after different degrees of damage are tested with electronic multi meter. The resistance values between clock signal lines are measured. Contrasting the resistance values of the CCD before and after damage, it is found that the resistances decrease significantly between the vertical transfer clock signal lines values. The same results are found between the vertical transfer clock signal line and the earth electrode (ground).At last, the damage position and the damage mechanism were analyzed with above results and SEM morphological experiments. The point damage results in the laser destroying material, which shows no macro electro influence. The line damage is quite different from that of point damage, which shows deeper material corroding effect. More importantly, short circuits are found between vertical clock lines. The full array damage is even more severe than that of line damage starring with SEM, while no obvious different electrical features than that of line damage are found. Further researches are anticipated in femto second laser caused CCD damage mechanism with more advanced tools. This research is valuable in EO countermeasure and/or laser shielding applications.

In this paper, Torrance-Sparrow and Oren-Nayar model is adopt to study diffuse characteristics of laser target board. The model which based on geometric optics, assumes that rough surfaces are made up of a series of symmetric V-groove cavities with different slopes at microscopic level. The distribution of the slopes of the V-grooves are modeled as beckman distribution function, and every microfacet of the V-groove cavity is assumed to behave like a perfect mirror, which means the reflected ray follows Fresnel law at the microfacet. The masking and shadowing effects of rough surface are also taken into account through geometric attenuation factor. Monte Carlo method is used to simulate the diffuse reflectance distribution of the laser target board with different materials and processing technology, and all the calculated results are verified by experiment. It is shown that the profile of bidirectional reflectance distribution curve is lobe-shaped with the maximum lies along the mirror reflection direction. The width of the profile is narrower for a lower roughness value, and broader for a higher roughness value. The refractive index of target material will also influence the intensity and distribution of diffuse reflectance of laser target surface.

A special waveform of CCD being irradiated by intense laser is explained and simulated. Its specialty is that reference level is altered and becomes equal with saturated data level, which can answer for CCD’s black video induced by laser and named as excessive saturation effect. Alteration of reference level has been explained by signal charges injection into the measuring well during reference time. In CCD, wells barriers are largely lower than channel stop. After that all transfer wells are crammed, many remained signal charges getting rid of clock’s control can be hold in channel, and move along it in thermal diffusion and self-induced drift. They can fill up the measuring well ahead of clock’s permission and alter reference level to saturated data level. Based on the explanation, the waveform is simulated on an equivalent circuit of CCD’s charge measurement structure, which is built on the platform of Multisim2001. The voltage sources and switches are used to manipulate the charge and discharge of a capacitor, which simulates the charge injection and resetting of measuring well. The clocks controlling switches represent the injection and reset clocks in CCD. To simulate clock’s impact on output, other capacitor is used to connect it to capacitor that represents the measuring well. The equivalent circuit is validated by the simulated normal waveform. Then, altering the clock and charging the capacitor ahead, the excessive saturation waveform is simulated, which validates the explanation to excessive saturation effect.

Thin metal flyers were launched from an aluminum-coated glass support using nanosecond Nd: YAG laser pulses at 532 nm. The velocity of the flyers was measured as a function of incident energy using a time-of-flight method. Also, the effects of flying distance, flyer’s diameter, and its thickness on the velocity were researched. The results showed that the flyer’s velocity depends strongly on laser-pulse energy, its flying distance, and its thickness. This study demonstrates the important influence of these conditions on flyer’s velocity, which is essential for finding the optimal conditions for flyer to achieve the highest velocity.

Two methods were described to quantitatively evaluate the damage of optical filters, which were through detecting the change of transmission coefficient and damaged area of optical filters. Based on the quantitative evaluation results, the laser-induced damage of optical filters was classified five damage degrees, which were undamaged, color changed, slight melt, middle melt and serious melt. The laser-induced damage was uncertain event because there were many uncertain factors to affect the laser-induced damage degree of optical filters. In view of the advantage of the Bayesian network in processing indefinite information, this paper emphatically studied the laser-induced damage degree assessment method of optical filters based on Static Bayesian network. A Bayesian model was constructed to assess the damage degree of filters. Upon our laser-induced damage experiments on the optical filters, the results of the quantitative evaluation were compared with the assessment results of Bayesian network model, which indicated that Bayesian network method was available to assess the laser-induced damage degree of optical filters.

The experimental setup was established for studying damage effects on silicon photoelectric detector materials induced by 800nm and 150fs repetitively-pulsed laser. The detector is irradiated by single shot and multiple shots respectively. The laser damage thresholds of silicon photoelectric detector material were measured. The surface morphologies of the material damaged by laser were analyzed. The surfaces damaged by laser with different energy were compared. The thresholds vary with the number of laser shots. According to the accumulation theory, the damage threshold is the power function of the shot number. Experimental results show that threshold of single shot that damages the silicon photoelectric detector is 0.156J/cm². The laser damage threshold decreases with the increasing number of laser pulses, but the minimum value exists. The damage is mainly caused by the mechanical effect rather than thermal effect. In fact, the thermal effect during the interaction is so small that it can’t even be observed. Resistivity of the silicon photoelectric detector irradiated by femtosecond laser decreases and finally tends to a constant value.

In this paper, fluid-solid thermal coupled computational models have been set up to simulate the subsonic nearwall airflow traversing a crater in target and heat transfer in target solid without phase transition in order to predict wall shear, heat flux and heat transfer coefficient on target surface and temperature field in the target under laser irradiation. The prototype of the model is the experiment zone of a flow simulation experiment facility, and the model was verified by the measured flow field data in it. The turbulence is modeled with Reynolds stress transport model. Laser irradiation is simulated with a beam of direct irradiation applied to the exterior boundary of the computational domain.

Experiments are performed to investigate the laser irradiation effects on thin aluminum alloy sheets subjected to tangential airflow. The wind blower generated airflow with a speed of about 100 m/s along the surface. For comparison, experiments in the absence of airflow are also conducted. Moreover, in order to know whether the combustion reaction takes place during the irradiation, we vary the composition of flow from air to nitrogen. The displacements of the sheets center are measured to see whether the tangential flow has a mechanical effect. The maximum temperature of the sheet is lower than 550 ℃ after 2 seconds irradiation with the laser power density of 173W/cm². Accordingly, the structural parameters of aluminum alloy do not have distinct change and so do the features of sheets. The temperature curves in the air flow and nitrogen flow keep the same and both lower than that in no flow case. Moreover, the displacements measured in three cases do not have obvious difference. These experiment results indicate that the combustion reaction can hardly happen and the tangential flow only has a cooling effect. The maximum temperature reaches 600 ℃ when the laser power density rises to 400 W/cm². Such a high temperature makes that the elastic modulus of aluminum alloy drops rapidly, which greatly softens the alloy sheets. The plastic distort of irradiated sheets confirmed this process. When the power density rises to 450W/cm² big melt-through phenomenon is observed and there is viscous dripping under gravity in the no-flow case. However, in air flow and nitrogen flow, we can see the removal of macroscopic unmelted pieces of aluminum alloy sheet. The results indicate that the tangential flow mainly has two effects including cooling the target and removing the unmelted metal when the material is fully softened.

The irradiation effects of 976nm continuous-wave laser on carbon fiber reinforced E-51 resin composite is studied experimentally, with a 0.4Ma tangential airflow or 0.4Ma tangential nitrogen gas flow on the target surface. In order to simulate the thermal response of fiber reinforced resin composite materials subjected to combined laser and tangential gas flow loading, a three-dimensional thermal response model of resin composite materials is developed. In the model, the thermal decomposition of resin is described by a multi-step model. The motion of the decomposition gas is assumed to be one-dimensional, for the case that the laser spot is significantly larger than the thickness of the sample. According the above assumption, the flow of the decomposition gas is considered in the three-dimensional model without introducing any mechanical quantities. The influences of the tangential gas flow, the outflow of the thermal decomposition gas and the ablation（including phase change ablation or oxidative ablation）of the surface material on the laser irradiation effects are included in the surface boundary conditions. The three-dimensional thermal response model is calculated numerically by use of the modified smooth particle hydrodynamics (MSPH) method which is coded with FORTRAN. The model is tested by experimentally measuring the temperature profiles during carbon fiber reinforced E-51 resin composite subjected to combined laser and tangential gas flow. The predicted temperature profiles are in good agreement with experimental temperatures obtained using thermocouples.

The air breathing vertical laser propulsion experiment refers to that in the air breathing mode the light craft under the irradiation of incident laser of vertical direction will turn pulse laser energy into the vertical propulsion thrust of the light craft and continue along the fixed rail upward propulsion flight. It is an important experiment to test the minimum single pulse energy, the optimization degree of light craft structure, and the characteristics of turning the laser energy into the thrust. The experiment is to be conducted dozens of meters in height away the ground generally. The article gives a detailed explanation of the whole process of the air breathing vertical propulsion test, including vertical propulsion light craft design, the connections design, the connections performance test, the frictional resistance detection and the whole process of movement performance test. A vertical propulsion tower was used to conduct the single pulse experiment and multi-pulse performance was predicted with a multiple-pulse thrust measuring system. The impulse coupling coefficient was estimated from fight height. Finally, through the experiments of air breathing vertical laser propulsion, the relation of the movement time and flight height was obtained. In the curve, the mean acceleration of the light craft can arrive to 6m/s² in the first 20 pulses and the propulsion height can reach 3.5m in 1.12s. After 0.65s, the acceleration of the light craft decreased significantly. The results of the article lay the good foundation for the laser propulsion launch system verification.

As one of the most significant methods to study laser propelled rocket, the numerical simulation of laser propulsion has drawn an ever increasing attention at present. Nevertheless, the traditional serial simulation model cannot satisfy the practical needs because of insatiable memory overhead and considerable computation time. In order to solve this problem, we study on a general algorithm for laser propulsion design, and bring about parallelization by using a twolevel hybrid parallel programming model. The total computing domain is decomposed into distributed data spaces, and each partition is assigned to a MPI process. A single step of computation operates in the inter loop level, where a compiler directive is used to split MPI process into several OpenMP threads. Finally, parallel efficiency of hybrid program about two typical configurations on a China-made supercomputer with 4 to 256 cores is compared with pure MPI program. And, the hybrid program exhibits better performance than the pure MPI program on the whole, roughly as expected. The result indicates that our hybrid parallel approach is effective and practical in large-scale numerical simulation of laser propulsion.

The laser coupling effect of material is a fundamental factor to influence laser interaction with matter. The coupling coefficient, which is the material absorptance of the input laser energy, depends on the surface conditions of materials, such as temperature, incident angle, surface airflow, oxidizing environment, and so on. To measure the laser coupling characteristics of materials, two typical online measuring apparatuses were developed in our laboratory. One is based on a conjugated hemi-ellipsoidal reflectometer, which is suitable to measure the laser coupling coefficients of different temperature in vacuum and air environments. The other is based on an integrating sphere and a simple airflow simulator, which can be applied to online measure the laser absorptance of materials subjected to surface airflow. The laser coupling effects on two types of structural materials, which are alloy steels and composite materials, are given in this paper. With the conjugated ellipsoidal reflectometer, the laser coupling effects on a typical alloy steel are investigated in different temperatures under the vacuum and air environment, and the experimental results are analyzed. According the results, metal oxidization plays a key role in the laser coupling enhancement effects. Especially, when the metal is subjected to high power laser irradiation in the high subsonic airflow, metal oxidization which is an exothermic reaction enhances the laser damage effect and the convective heat loss is negligible. Finally, the laser coupling effects on a typical composite material subjected to airflow are studied by using the integrating sphere with an airflow simulator, and the experimental results of laser absorptance during the laser ablation are presented.

Based on the invariable stretching stress preloading device, the experimental investigation on damage effect of 30CrMnSiA steel structure specimen by continuous laser was carried out. While the stress is between 660MPa and 1140MPa, the average laser power density is between 110W/cm² and 330W/cm², we can get the conclusions as follow: (1) When the preloaded stretching stress increases, the necking phenomenon becomes unobvious. (2) When the preloaded stretching stress increases, both the rupture time and rupture temperature decrease monotonously. (3) When the laser power density increases, the rupture time decreases monotonously. (4) When the preloaded stretching stress or laser power density increases, the rupture threshold decreases monotonously. (5) The strain of the specimen before necking is small, and the specimen metamorphoses during necking period and the deformation of specimen is centralized in the necking region.

Precise simulation of transient electrical behaviors of photodetectors under laser irradiation is becoming an increasingly concern. It not only can allow a detailed study and analysis of complex phenomena that cannot be carried out by experiments, but gives valuable information about the physical mechanisms which ultimately determine the response of the photodetectors. Finite difference numerical technique is adopted in the simulation to calculate the current response of photodetectors under pulsed laser irritation in this paper. To simulation the behaviors of photodetectors under pulsed laser irritation, the transport and trapping of carries and external circuit effects, including load resistance, junction capacitance, and parasitic capacitance, are considered. The basic equations governing the carrier behaviors are solved, including Poisson’s equation, the carrier motion equations, and the carrier continuity equations. The simulated transient carrier density and velocities are present, as well as corresponding transient electric field distributions. The behaviors of electrons and holes and its contributions to the external current response are analyzed. Then a general and brief image of the transient progress of photodetectors under pulsed laser irritation is established. How the carrier is induced, transported, and trapped and whether they make any significant contribution to the external current response are discussed. Besides, bias dependent response is also studied. Higher bias will improver the behaviors of photodetectors under pulsed laser irritation. The simulated results and theory analysis will show valuable clue for future research on the behaviors of photodetectors irradiated by pulsed laser.

The photoelectric parameters degradation of Si-based PIN photodiodes irradiated by 1064 nm millisecond Nd:YAG laser has been measured. The samples were the commercial silicon PIN photodiodes BPW34 with plastic package. The applied laser fluence levels range from 20J/cm² to 1400J/cm². Surface damage morphology, dark current and sensitivity were investigated for the irradiated photodiodes. It has been shown that the dark current was the first and the most sensitive degradation parameter, and we believe that the dislocation introduced by the tangential component of thermal stress in the [111] and [110] direction was the main reason. The sensitivity decrease until the dark current reach to μA magnitude and the surface have melted seriously, the finite element method was used to calculation the dopant redistribution process. It shows that the degradation of sensitivity depends greatly on the process under various applied laser fluencies.

Laser drilling was attempted to make closely spaced cooling holes on YSZ coated metal substrate. As a preparation work for laser drilling, the laser irradiation effect on YSZ coating was investigated. Laser irradiation experiment was performed using a continuous fiber laser (λ=1070nm), with maximum power density of approximately 2000W. The original and irradiated coatings were observed and analyzed through SEM images. Through the overall top surface images and low magnification cross-section SEM images, the destruction features of YSZ coating were obtained. With low laser energy input, the coatings were destructed in terms of crack imitation and propagation; with high laser energy input, the coatings were melted and pushed away. The laser destructive effect is more sensitive with the laser power increasing than with the expanding of irradiation time. Through high magnification SEM images of cross-section, the character of the microstructure of the laser irradiated YSZ coating was summarized and the formation mechanism was concluded. The laser melted YSZ coating can be divided into three layers, including the isometric crystal layer, the columnar crystal layer and the reserved original YSZ layer. The formation mechanism was related to the rapid solidification process and thermal dissipation condition.

Ultra high temperature ceramics (UHTCs) were thought to be candidates for laser protective materials due to their high melting point, thermal shock and ablation resistance. The ablation behaviors of UHTCs like ZrB2 and its composite had been intensely investigated by the means of arc, plasma, oxyacetylene ablation. However, the ablation behavior under laser irradiation was still unknown by now. In this paper, the dense bulk composites of ZrB2_{/Cu were successfully sintered by spark plasma sintering (SPS) at 1650 degree C for 3min. The reflectivity of the composites} measured by spectrophotometry achieved 60% in near infrared range and it decreased with the increasing wavelength of incident light. High intensity laser ablation was carried out on the ZrB₂/Cu surface. The phase composition and microstructure changes before and after laser irradiation were characterized by X-ray diffraction and SEM respectively. The results revealed that the oxidation and melting were the main mechanisms during the ablation processing.

The process of long pulse laser(1ms) interaction with the aluminum plate was analyzed using Mach-Zehnder interferometer in this paper. A continuous semiconductor laser with about 50mW power and 532nm wavelength was used to detect the flame which induced by long pulse laser interaction with the aluminum plate. A high speed camera was used to capture the interferograms. The exposure time of the high speed camera is about 2 microseconds. And the frame rate is 2130fps. The high-speed camera and the long pulse laser pulse was synchronously controlled by the four-channel digital delay (Stanford Research Systems DG535).The FFT(Fast Fourier transform ) analysis is applied to extract the phase of the interferograms. The results provide an understanding of the process of long pulse laser drilling of the Al target.

In this paper we build an experimental apparatus to measure the reflectivity and temperature of the foil in different conditions. The experimental results show that the growth of oxide film can be divided into 3 stages which corresponding to logarithmic, linear and parabolic rate law. A mathematical model is introduced to explain the phenomena observed in experiment. Numeral calculations are made for 30CrMnSi steel while cw-laser wavelength is 1.07μm. The numerical solutions are in agreement with the experimental data.

The derivation of an elementary figure of merit shows that the attainment of ultrahigh intensities suitable for probing the dynamics of the vacuum state is significantly facilitated by the use of coherent x-ray sources in the kiloelectronvolt regime. For the Xe(L) system at ħω ~ 4.5 keV, estimates indicate that an intensity sufficient for the observation of vacuum harmonic generation (~ 10²⁷ W/cm²) can be reached with pulse energies in the 5 - 50 mJ range. The corresponding pulse energy for the Schwinger/Heisenberg Limit (~ 4.6 × 10²⁹ W/cm²) is ~ 1.5 J. Measurements conducted at intensities in this range are expected to yield information about the cosmological “Dark Energy”, the mysterious centrally important entity that constitutes ~ 73% of the Universe.

In order to improve the total laser-proton energy conversion efficiency, a nanobrush target is proposed. Compared with foil target, the sheath field on the rear surface of nanobrush target is increased near 100% and the energy efficiency from laser to proton is prompted more than 70%. Meanwhile, the proton beam is well collimated with divergence angle less than 30degree. As sub-wavelength nanolayered target and conical targets both enhance laser absorption compared with foil targets, we propose a conical nanolayered target in trying to improve coupling efficiency. Compared with nanolayered target, the energy coupling efficiency is enhanced from 34% to more than 68%. Detailed simulations indicate that this enhancement is attributed to both oblique incidence and focusing of the conical target. Moreover, the conical nanolayered target collimates the hot electrons better. The conical nanobrush target is used to improve the total proton energy-conversion efficiency in proton beam acceleration. Results indicate a significant enhancement of the number and energies of hot electrons through the target rear side of the conical nanobrush target. Compared with the plain target, the field increases several times. We observe enhancements of the average proton energy and total laserproton energy conversion efficiency of 105%. This enhancement is attributed to both nanobrush and conical configurations. The proton beam is well collimated with a divergence angle less than 28degree.

Two-dimensional near-wavelength microstructures have been fabricated on a copper film and a silicon wafer by femtosecond vector optical fields with different spatial polarization distribution, at a central wavelength of 800 nm, pulse duration of ∼70 fs, and a repetition rate of 1 kHz. Laser-induced ripples appear at the ablated region on silicon when the laser fluence is above the ablated threshold. When the number of the irradiated pulses increases, ripples with interspace larger than the wavelength could be observed, while the dimension of the ablated region has a slight variation. In the induced microstructures on a copper film, the microstructures in a ring have been observed under the irradiation of a few pulses. Under the irradiation of the multipulse femtosecond vector field, differently from the condition of the silicon, the induced microstructures on the metallic copper surface exhibit the anisotropic extending feature dependent on the polarization distribution of the vector field. The physics behind this unique feature is the anisotropic excitation and propagation of surface plasmon, caused by the coupling of the subsequent irradiation pulses with the existing microstructure. In this case, the surface plasmons resonance in the induced 2D microstructures is closely related to the induced grating structures on the surface.

In this paper, the anisotropic focusing technique is used to make a novel streak tube. The salient features are the introduction of both temporally focusing electrodes and spatially focusing electric quadrupole lens. The simulation showed that physical temporal dispersion of 0.38 ps and edge spatial resolution of 56 lp/mm can be achieved. The Nd:YLF 8ps pulse laser was used to calibrate the performance index of streak camera. The static and dynamic spatial resolutions are 35 lp/mm and 25 lp/mm respectively. The dynamic range more than 950:1 and time resolution 8ps can be reached. Furthermore, the magnifications in slit and scanning direction can be adjusted respectively, so it is very convenient to select amplification needed when it is coupled with KB microscope.

The radial structure of core temperature and density is very important to benchmark theory simulation codes in Inertial confinement fusion (ICF) studies. In this article, we gave a method to determinate the radial structure of core temperature and density by using the normalized intensity of core experimental x-ray image. The core emission model uses the average atom model (AA) and the radiation transport model assumes the local thermo dynamic equilibrium model (LTE). Calculated results show that: the full width at half maximum of core temperature is about 39.4μm which indicate that the hot spot diameter is such value and the full width at half maximum of core density is about 5μm. The hot spot convergence and the shell in-flight aspect ratio (IFAR) can be deduced approximately 7 and 7.5 respectively. The above assist us to better understand the implosion physics, and provide more information for benchmarking the simulation codes.

Characteristics of shock wave as well as its evolution of aluminum plasma produced by nanosecond YAG laser is investigated by time-resolved optical shadowgraph images. Experimental results show that shock wave is strongly influenced by the laser parameters and target arrangement. Shock waves from aluminum plasma and air plasma are observed simultaneously by shadowgraphs when the distance from lens to target surface (DLTS) is longer than the lens focal length, and a narrow bright “line” is observed in the region where shock waves from Al plasma and air plasma meet. The longitudinal expansion velocity of shock wave from Al plasma is largely influenced by DLTS and laser intensity as well, and it increases with laser intensity at the early stage of plasma expansion and reach to a maximum of 8.1×10⁴ m/s.

Electron acceleration in the wakefield by adding a dense-plasma wall in the underdense plasma during the mode transition from laser wakefield to plasma wakefield acceleration is investigated by particle-in-cell simulations. The selfinjected electrons from the laser wakefield acceleration (LWFA) scheme is quasi phase-stable accelerated forward because of the longitudinal contraction of the bubble. The electron bunch generated from the LWFA scheme drives a plasma wakefield after the laser pulse is depleted completely. Two high-quality electron bunches with narrow energy spread and low emittance is obtained.

In this paper, an atmospheric pressure argon plasma plume generated by sinusoidal power input of moderate frequency (kHz range) and designed with dual-power electrodes is characterized and studied. Particularly, the effect of driving frequency in the 60–130 kHz range on the argon plasma discharge characteristics is investigated based on a detailed electrical and spectroscopic diagnostics. And, temporal and spatial optical emission spectroscopy is used to measure the plasma parameters, of which the excitation electron temperature is determined by the Boltzmann’s plot method whereas the electron density is estimated using the stark broadening of the hydrogen Balmer Hβ line. It is shown that at constant applied voltage and gas flow rate, the increase of driving frequency in the range of 60–100 kHz exerts no significant influences on discharge parameters. While once the driving frequency exceeds a certain value of about 100 kHz, the discharge becomes intense abruptly and the corresponding discharge parameters increase drastically with the driving frequency. Detailed analysis about the effect of driving frequency on discharge characteristics is presented and two different dominant electron loss mechanisms, namely transport-dominated loss and diffusion-dominated loss, are proposed to account for the distinct effects of the driving frequency on argon discharge characteristics.

High power acoustic sources, generated by laser-induced breakdown when high power laser is focused into water, have extensive application prospects in laser medicine and ocean exploration. Combining the models of sound column and plasma disc in laser-induced breakdown generated sound field, a plasma cylinder model is established. The directivity of the sound field, and it’s characteristics are mapped and analyzed through numerical simulation, as well as theoretical analysis. An experiment is designed and performed to verify the plasma cylinder model. The experimental results, which are in a good agreement with the simulation, reveal the maximum pressure amplitude of the acoustic signals is at the direction vertical to the light propagation, and present a distinct major-lobe and minor-lobes.

(ultraviolet). To generate strongly coupled plasmas (SCP) by high power excimer laser, an Au-CH-Al-CH target is used to make the Al sample reach the state of SCP, in which the Au layer transforms laser energy to X-ray that heating the sample by volume and the CH layers provides necessary constraints. With aid of the MULTI-1D code, we calculate the state of the Al sample and its relationship with peak intensity, width and wavelength of laser pulses. The calculated results suggest that an excimer laser with peak intensity of the magnitude of 10¹³W/cm² and pulse width being 5ns - 10ns is suitable to generate SCP with the temperature being tens of eV and the density of electron being of the order of 10²²/cm^-3. Lasers with shorter wavelength, such as KrF laser, are preferable.

Laser Supported Absorption Wave (LSAW) is an important content in laser propulsion research, which can be divided into Laser Supported Detonation Wave (LSDW) and Laser Supported Combustion Wave (LSCW) according to that whether the wavefront of LSAW is separated from the wavefront of Precursor Shock Wave or not. Maintaining LSAW need the incident laser with certain energy, in result the laser threshold of LSDW is higher than that of LSCW. In 1965, the pneumatic dynamics model is proposed by Paйзep firstly, in which LSDW is regarded as a strong discontinuity without thickness transmitting with supersonic speed, where the incident laser is completely absorbed so that the wave is forward. LSDW compresses the gas in front of it, with the result that the gas ionizes by temperature increasing and absorbs laser, then becomes the new wavefront. Based on the fluid mechanical formula of one-dimension LSDW, influence of incident laser intensity on the speed of LSDW and the pressure, temperature and intensity of gas behind LSDW is analyzed in this paper, primarily the range and trend of the speed of LSCW and the parameters of gas behind LSDW are deduced in theory. The speed of LSDW is in direct ratio with 1/3 of incident laser intensity, and the pressure and temperature of gas behind wave is in direct ratio with 2/3 of incident laser intensity. Along with laser power increasing, the speed of LSCW is gradually close to the speed of precursor shock wave, at the moment LSDW comes forth. While the ratio of the speed of LSAW to sonic speed is more than 1, LSAW is LSDW. Or else, while the ratio of the speed of LSAW to sonic speed is less than 1, LSAW is LSCW. On the basis of speed formula of LSDW and sound speed formula in gas, the threshold of the laser intensity to keep LSDW is discussed in this paper, and the theoretically calculated results are compared with experimental results reported in some documents. In fact, because that plasma is composed of positively charged ions and negatively charged electrons, and the charged particles have Coulomb interaction, which bring about that the internal energy and the pressure of gas is somewhat different from ideal gas, plasma should not simply be discussed as ideal gas. In view of the internal Coulomb interaction of plasma, the speed of LSDW is increasing and the pressure and temperature of gas behind wave is descending. Finally, the deviations of plasma with Coulomb interaction from ideal gas are put forward, and how to correct these deviations is analyzed.

Optical emission of the plasma generated on metal hydride target by pulsed laser beam from an Nd:YAG laser was used to investigate the temporal evolution of the line relative intensity, ion (electron) temperature (Te) and electron density (Ne). From relative emission intensities of the atomic and ionic species, the ion temperature using Saha- Boltzmann plots were evaluated. The electron density was determined utilizing the Stark broadening of the Hα-line at 656.27 nm. It was found that numerous lines of double-charged metal ion were visible only at the first 200 ns, and the single-charged metal ion reached the line intensity maximum. The relative intensities of ion line decrease with the increasing time, as opposite to atomic line became more intensive after 1 μs. The max electron density and ion temperature was between 400 ns and 600 ns, then ion temperature decreased from 1.3 eV down to 0.9 eV at the following 4 μs, but the electron density varied so irregularly that further investigation was required in furture.

The design and performance of Optical frequency modulation continuous wave (OFMCW) coherent laser radar is presented. By employing a combination of optical heterodyne and linear frequency modulation techniques and utilizing fiber optic technologies, highly efficient, compact and reliable laser radar suitable for operation in a space environment is being developed.We also give a hardware structure of the OFMCW coherent laser radar. We made a detailed analysis of the measurement error. Its accuracy in the speed range is less than 0.5%.Measurement results for the movement of the carrier has also made a detailed assessment. The results show that its acceleration vector has better adaptability. The circuit structure is also given a detailed design. At the end of the article, we give the actual authentication method and experimental results.

Typically, we use Klett-Fernald method for retrieving aerosol optical properties. However, the results from these methods critically depend on the lidar ratio, thus affecting the accuracy of the inversion results. In this paper, we adopted a new method to retrieve the vertical distribution profiles of aerosol backscatter coefficient, aerosol extinction coefficient and lidar ratio over Beijing region by combining rotational Raman - Mie lidar and CALIPSO(Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations). The results were compared with the results determined by the conventional method, which shows a good agreement. Compared with the conventional method, the results from this new method are more reliable and less noisy, which provide richer information for researching the atmospheric aerosol properties over Beijing region.

A Q-switched Nd: YAG laser (with a wavelength of 532 nm and a pulse width of 15 ns) was used to ablate hexahydrol, 3,5-trinitro-l,3,5-triazine (RDX) in the air. The plasma emission spectra were recorded by an intensified charge-coupled device (ICCD) camera. The results showed that the plasma existed in the process of laser ablation of RDX. In the ultraviolet area, the main spectral lines were C I (187.46 nm and 223.01 nm), C II (323.1 nm) and N II (243.72 nm and 332.9 nm), while the dominating emission lines in the visible area were N II (393.9 nm and 454.7 nm), O II (490.75 nm) and O III (401.2 nm). Under experimental conditions, the intensities of the main peaks grew obviously with the increasing of the pulse delay, but laser energy didn’t have so much effect on the spectra. The ionization of the air almost did not influence plasma emission lines of RDX.

Planar Laser-Induced Fluorescence (PLIF) technique, which is a non-intrusive, fast-response diagnostic method, has been widely used in measurement of various complex flow fields. Both cold flowfield^[1-4] and combustion flowfield^[5] have made use of PLIF for diagnosis. According to the different flow field and investigation objects, parameters such as fluorescence tracer molecule, laser wavelength, and so forth should be selected seriously in order to obtain the information concerned. This technique was used to investigate complicated flow structure of mixing between transverse jet and supersonic flow, in which acetone and OH radicals were chosen as the fluorescence tracer molecules in the experiments of cold flow and combustion flow respectively. During cold flow measurements, air was used as both the transverse jet and supersonic flow, and liquid acetone was gasfied before adding into the transverse jet, which was excited by laser sheet of 266nm. During combustion flow measurement, ethylene was used as the transverse fuel jet, and combustion between air and ethylene was sustained by plasma discharge. Laser sheet of 283nm was used excite the intermediate product of OH radicals. Fluorescence images were recorded by the intensified CCD camera after filtering interfere light. Both results show that PLIF displays as a credible and valid method for investigating complicated cold flowfield and combustion structure, so long as chosing appropriate fluorescence tracer molecule, laser exciting wavelength, optical filter, et al.

Laser induced fluorescence has the potential to get two dimension temperature and concentration map in combustion. For understanding the fluorescence technology exactly, A detailed experiment has been developed to investigate the fluorescence spectrum. The time variation of spectrum is first presented by changing the pump-probe time delay. And this is followed by demonstrate the response of fluorescence to laser excitation. As showed by the experiment result, The intensity ratio of the (1, 1) and (0, 0) fluorescence band was varied both with time and the exiting laser line, we attribute this phenomenon to the difference rotational distribution of excited OH. And the new rule, which exciting a specific rotational level in the A²Σ(υ ' =1) excited state from two difference rotational levels in the X ²Π(υ " = 0) ground state, was experimental confirmed, and this will be a foundation to the future two line laser induced fluorescence thermometry.

Plume generation and expansion performance measurements have been performed with ns-shadowgraphy time resolved method on laser micro ablation. The optical display method of micro jet plume characteristics is discussed and the plume character is measured and analyzed to research the relationship between coupling mechanics and plume dynamics. The micro laser ablation properties of different commercial ploymers are compared to find out the ideal micro laser thruster fuel to achieve propulsion performance improvement. The plume generation and expansion character is analyzed by the shock wave and ablation product evolution. Shock wave and ablation product jet could be formed in the air condition, and the velocity is different. Normally, the shock wave is faster than the jet, but the inverse situation is still observed that could be taken as signal of the higher specific impulse. Nine common polymers were tested and compared, the results show that: polyvinyl chloride ( PVC ) material is the best choice of commonly used polymer material. A velocity of 820m/s of shock wave formed by PVC ablation could be obtained, which is highest in the chosen polymers, while the velocity is 844m/s for Al, and there are more ablation product could be found for PVC. The result indicates that ablation efficiency of PVC is the best, and PVC is the priority fuel material for the better propulsion performance, easy machining and storage.

The velocity components of the high temperature high speed flow produced by a simulative device were diagnosed by single-line hydroxyl tagging velocimetry. The simulative device was driven by H2/air combustion gas, worked like a shock tube, held about 10-ms. The HTV tagging lines were put after the exit of device, and the experimental images at flow’s different regions were acquired through changing the tagging lines’ positions corresponding to the exit of device. And the velocity components along the device axis on tagging lines were calculated from the images. The results indicated that the velocity values of the flow in compress region were much slower than those in expansion region. Between the flow’s first expansion and compress regions, the velocity values at center were higher than those at both sides, but in the flow’s second expansion region, the velocity values at center were slower than that at both sides.

A mobile diagnostic system based on Unstable-resonator Spatially Enhanced Detection Coherent anti-Stokes Raman Scattering (USED CARS) geometry was established, which was used for temperature measurements in a model supersonic combustor. The temporal and spatial resolution of this mobile CARS system are 10ns and Ф0.1mm×5mm respectively. Single pulse nitrogen CARS spectrum with high signal to noise ratio(SNR) were obtained at the exhaust of model combustor through high stability optical design, and the temperatures were acquired by Levenberg-Marquarat fitting algorithm. The mean temperature of the unstable combustion is 1412K, and the mean temperature of the stable combustion is 1705K.

Laser diagnostic techniques play an important role in combustion research. Four laser-based measurement techniques are developed for harsh combustion environments. In the measurements of aeroengine turbine combustor, two dimension temperature distribution of a interior cross-section was obtained by self-designed 2D-scan coherent anti-stokes Raman scattering (CARS) system, and the main species concentration in the region above the primary hole were measured by spontaneous vibration Raman scattering (SVRS). In the investigations of a supersonic combustor, the line-of-sight averaged temperature was on-line acquired by tunable diode laser absorption spectroscopy (TDLAS) technique, and the velocity components near the exit of combustor were obtained by single line hydroxyl tagging velocimetry (HTV). These measurement activities demonstrate that laser diagnostic techniques have well performance in harsh environments, such as unclean combustion, strong vibration and high background emission. These diagnostic techniques can provide useful experimental data for validating computational fluid dynamics (CFD) model and evaluating combustor characteristics.

Tunable Diode Laser Absorption Spectroscopy (TDLAS) technique has many significant advantages such as non-intrusive compared with traditional combustion parameter measurement techniques. In this paper, according to the absorption lines optimization criterions, the 7444.352+7444.371 cm^-1 and 7185.597 cm^-1 line pair of water vapor (H2O) is selected for the temperature measurement of combustion environment in 900-1600K region, and two most important influencing factors (temperature and pressure) are analyzed by simulation of absorption spectrum based on HITRAN. Therefore, TDLAS system using the 7444.352+7444.371 cm^-1 and 7185.597 cm^-1 line pair based on Time-Division-multiplexing (TDM) strategy has been designed. This TDLAS system has been applied for the temperature measurement in the exhaust of Rocket Based Combined Cycle (RBCC) engine. Compared with the pressure measured by the pressure transducer in combustion chamber, the tendency of temperature measurement has well agreement with the pressure. The result of temperature measurement using TDLAS technique has great importance to the evaluation of RBCC combustion efficiency.

The effects of injection parameters on atomization of aviation kerosene (RP-3) were studied using a laser diffraction particle size analyzing system. The test results indicated that Sauter mean diameter (SMD) decreased with the increase of injection temperature. There was a critical temperature for flash evaporation, at which SMD had a sharp decrease. The critical temperature fell at first and then rose with the increase of injection pressure; however, the diameter of a centrifugal nozzle had little influence on the critical temperature. Sauter mean diameter didn’t follow the conventional law after flash evaporation. A simple and empirical correlation between critical temperature for flash evaporation and injection parameters was developed from the experimental data, which can be used to evaluate critical temperature for flash evaporation.

This paper describes the CO concentration and gas temperature distribution measurements behind a strong shock wave in the simulated Martian atmosphere by an optical diagnostic system. The strong shock wave (6.31 ± 0.11 km/s) is established in a shock tube driven by combustion of hydrogen and oxygen. The optical diagnostic system consists of two parts: the optical emission spectroscopy (OES) system and the tunable diode laser absorption spectroscopy (TDLAS) system. For OES system, high temporal and spatial resolution experimental spectra of CN violet system (B²Σ+→X²Σ+, v = 0 sequence) have been observed. Rotational and vibrational temperature distribution along the shock wave is inferred through a precise analysis of high-resolution experimental spectra. For TDLAS system, a CO absorption line near 2335.778 nm is utilized for detecting the CO concentration using scanned-wavelength direct absorption mode. Combined with these experimental results using OES, CO concentration in the thermal equilibrium region is derived. The detected average CO concentration is 7.46 × 10¹² cm^-3 with the average temperature of 7400 K ± 300 K, which corresponds to the center fractional absorption of 2.7%.

A single-shot transient-grating frequency-resolved optical gating (TG-FROG) device was set up to measure UV ultrashort pulse laser with pulse duration within 10ps.The performance of the device was demonstrated by experimental data measured on discharge-pumped KrF laser which is operated in 10Hz repeated frequency mode,and on electronbeam- pumped KrF laser which is only operated in single-shot mode.For the former,the TG-FROG can distinguish the changes of the pulse shape,spectrum and phase when the pulse chirp is changed.For the later,the TG-FROG finds that the pulse shape has multiple peaks whose pulse duration is about 2ps,and the spectrum is modulated whose bandwidth is about 1.3nm,and the corresponding phases present parabolic structure.

High power excimer laser has essential applications in the fields of high energy density physics, inertial fusion energy and industry owing to its advantages such as short wavelength, high gain, wide bandwidth, energy scalable and repetition operating ability. This overview is aimed at an introduction and evaluation of enormous endeavor of the international high power excimer laser community in the last 30 years. The main technologies of high power excimer laser are reviewed, which include the pumping source technology, angular multiplexing and pulse compressing, beam-smoothing and homogenous irradiation, high efficiency and repetitive operation et al. A high power XeCl laser system developed in NINT of China is described in detail.

Electric breakdown and non-self-sustained electric discharge were triggered and guided by a train of ultrashort sub-TW ultraviolet (UV) pulses overlapped with a long free-running UV pulse of a hybrid Ti:Sapphire-KrF laser facility. Photocurrent sustained by this train is two orders of magnitude higher, and electric breakdown distance is twice longer than those for the discharge triggered by the long UV pulse only. UV filaments of ~100 m length were observed when transporting the laser radiation over the long distance.

With the rapid development of laser applications, single elements of diode lasers are not able to meet the increasing requirements on power and beam quality in the material processing and defense filed, whether are used as pumping sources or directly laser sources. The coupling source with high power and high beam quality, multiplexed by many single elements, has been proven to be a promising technical solution. In this paper, the authors review the development tendency of efficiency, power, and lifetime of laser elements firstly, and then introduce the progress of laser beam combining technology. The authors also present their recent progress on the high power diode laser sources developed by beam combining technology, including the 2600W beam combining direct laser source, 1000W fiber coupled semiconductor lasers and the 1000W continuous wave (CW) semiconductor laser sources with beam quality of 12.5×14[mm. mrad]².

Diode-pumped alkali-vapor laser (DPAL) is a kind of laser attracted much attention for its merits, such as high quantum efficiency, excellent beam quality, favorable thermal management, and potential scalability to high power and so on. Based on the rate-equation theory of end-pumped DPAL, the performances of DPAL using Cs-vapor collisionally broadened by helium are simulated and studied. With the increase of helium pressure, the numerical results show that: 1) the absorption line-width increases and the stimulated absorption cross-section decreases contrarily; 2) the threshold pumping power decreases to minimum and then rolls over to increase linearly; 3) the absorption efficiency rises to maximum initially due to enough large stimulated absorption cross-section in the far wings of collisionally broadened D2 transition (absorption transition), and then begins to reduce; 4) an optimal value of helium pressure exists to obtain the highest output power, leading to an optimal optical-optical efficiency. Furthermore, to generate the self-oscillation of laser, a critical value of helium pressure occurs when small-signal gain equals to the threshold gain.

The working mechanism of the non-chain pulsed DF laser is analyzed in this paper, then the glow discharge with the method of UV-preionized discharge is displayed, and finally the experimental investigation on the output characteristics of non-chain pulsed DF laser is done. With SF₆, which is non-toxic and non-corrosive, and D₂ as the active medium, the dependence of the output characteristics of pulsed DF laser on the gas mixture ratio and the total pressure are investigated. In the experiment, the optimal gas mixture ratio of SF₆-D₂ and total pressure are 10:1 and 10.5kPa, respectively. At the same time, by making a measurement on the output spectrum of DF laser with a DF laser spectrum analyzer, 17 P-branch transition lines are achieved and the majority of output energy is concentrated on several lines near the 3.876μm line. The laser beam divergence angles in horizontal and vertical directions are 1mrad by using the laser spot ablation method. At the charging voltage of 39kV, under the best working condition(SF₆: D₂ = 10:1, P_total= 10.5kPa), the maximum single pulse output energy of 3.58J, pulse duration of 215ns, peak power of 16.65 MW, and electro-optical conversion efficiency of 2.08%, are obtained.

This paper is focused on the research of SSD and CPP carried out on TIL. A bulk phase modulator with 9.2-GHz modulation frequency is adopted in SSD. The output spectrum of the phase modulator is stable and the residual amplitude modulation is small. FM-to-AM effect caused by free-space propagation after using smoothing by spectral dispersion is theoretically and experimentally studied. Results indicate inserting a dispersion grating in places with larger beam aperture alleviates the FM-to-AM effect, suggesting minimizing free-space propagation and adopting image relay. Experiments indicate when the number of color cycles (N_c) adopts 1, imposing of SSD with 4.26 times diffraction limit (TDL) did not lead to pinhole closure in the spatial filters of the preamplifier with 20 TDL and main amplifier with 26 TDL. Experimental results also indicate SSD didn’t influence the load capacity of the laser facility. The contrast of the 440-μm diameter focal spot with 95% energy included using SSD and CPP drops to 0.47, comparing to 1.71 not using SSD and CPP. When the pulse width of the third harmonic wave is 1 ns and the energy is 1115 J, no damage is found in CPP and other final optics. The experiments solves some key technical problems using SSD and CPP on high-power laser facilities, and provides a flexible platform for the laser-plasma interaction experiments.

The effort of ISI excimer pulse shaping based on gain depletion for inert confined fusion (ICF) in Heaven-I KrF laser system was introduced. The 24ns ISI pulse has been self-shortened to 10ns with a unique set-up call pulse feedback based on gain switch, which can be combined with the EFISI for the high uniformity beam profile. The shorter ISI pulses with the duration of 3~10ns have been obtained with laser quenching. The further proposal to generate a complex pulse shape for ICF based on gain depletion was discussed in this paper.

An efficient and compact green laser at 523.5 nm was generated by intracavity frequency doubling of a diode end-pumped conductively cooled Q-switched Nd:YLF laser at 1047 nm. With an incident pump pulse energy of 28.6 mJ at 250 Hz repetition rate, pulse energy of 8 mJ was obtained with a pulse width of 10 ns, corresponding to an optical– optical conversion efficiency of 28%. The beam quality factors were M_x ² =1.35,M_y ² =1.21.

Two kinds of Q-switched ultraviolet lasers using an acousto-optic modulator and an electro-optic modulator in the same cavity structure are demonstrated, with type I phase-matched LBO as second harmonic generation crystal and type II phase-matched LBO as third harmonic generation crystal. For acousto-optic Q-switched UV laser，a maximum average power of 6.3W with the shortest pulse width of 12 ns was obtained at the repetition rate of 22 kHz when the pump power reached 52.4 W. The optical conversion efficiency was up to 12%. Then we used a La₃Ga₅SiO₁₄ crystal electro-optic modulator to replace the acousto-optic modulator. The 1.29W output power at 355nm wavelength was obtained at the repetition rate of 10 kHz when the pump power was increased to 20.4W, and the UV laser pulse width was as short as 9.6ns.The optical conversion efficiency was up to 6.3%.

In the working process of chemical oxy-iodigenne laser(COIL), the change of iodine pool pressure is complicated. As a result, it causes some mis-judgements, such as the damage of heater and the leakage of iodine steam. Further more, when the heater electric circuit is in a single working status, and after the heater switch is on or off, there exists a buffer time for the stabilization of iodine pool pressure, which is a relatively long time, and the minimum buffer pressure exceeds to 19 torr . Of course, it increases the preparing time for steady operation of laser, and reduces the quality of laser beam. In this paper, we study the iodine pool pressure of COIL in non-equilibrium condition, and analyze the mutation and the serious buffer phenomenon of iodine steam pressure. At the same time, we design an automatic control system for iodine pool pressure, which consists of five modules, such as data collection, automatic control, manual control, heater electric circuit, and the setting and display of pressure. This system uses two kinds of heater electric circuits, in this way, the serious buffer phenomenon of iodine pool pressure is effectively avoided. As a result, the maximal buffer pressure reduces to 4 torr, this makes sure that the iodine steam pressure is suitable for the operation of COIL, which produces a good condition for the steady operation of laser system and an excellent laser output.

The laser performance of a short-length Yb-doped rod-type photonic crystal fiber (PCF) laser is studied experimentally both in the three-level scheme and quasi-four-level scheme in this contribution. In the free oscillation mode, the rod-type PCF laser produce 13.6 W output power on the quasi-four-level system with center wavelength of 1030 nm. The laser operating on the three-level system is obtained with the introduction of specialized feedback around the 976 nm radiation. Up to 7 W output power is generated with wavelength centered in 978 nm.

Cross relaxation (CR) process in thulium ions is described. Performance of Tm-doped fiber lasers with different dopant concentrations is evaluated numerically with and without CR. Simulation shows that CR process can not only improve the slope efficiency and output of the laser system, but also lower the lasing threshold and extend the growth momentum of the laser performance. Backward LD-clad-pumped Tm-doped fiber lasers are built with Tm-doped fibers of different doping levels. A maximum output of 35.3W around 2μm is obtained with a slope efficiency of 47.2% from the 4.5wt.%- doped fiber laser while a higher slope efficiency of 54.1% was achieved from the 6.8wt.%-doped fiber laser. And, modeling shows that these laser systems are much more efficient than that without CR process.

A method for direct laser beam diagnostics based on fiber array is introduced. The designing principle and configuration of the method are presented. The experimental results show that it can provide laser power density distribution information with a high spatial resolution better than 3mm and with an error of measurement less than 3%. The theoretical analysis by finite element method(FEM) for laser radiation indicates that this method should be used to measure the high energy laser beam with diameter of several hundred millimeters for tens of seconds. In addition, the results of fiber array technique are compared, qualitatively, with the spatial beam profile obtained by a near infrared charge coupled device(NIR-CCD). These two methods yield consistent results.

In the development of high energy laser (HEL) beam diagnostic equipment with optical attenuation by dielectric multilayer films reflector, in order to fulfill the sampling uncertainty request of the system, the transmittance of the attenuator should keep as a constant or only vary in a small range when the incident angle of laser changes. To address this, we analyzed the principle of the conventional dielectric multilayer films reflector and put forward a new and simple offset-central-wavelength multilayer films reflector (OCWMFR) involving no change of the dielectric multilayer films materials and basic fabrication process. Theoretical simulation and experimental results show that the reflector has a good transmittance consistency and can meet the attenuation and sampling requirement of HEL beam diagnosis.

A synthesis of the calorimetric and photoelectric method on the high energy laser beams measurement is presented. Data fusion of the two kinds of detector units is achieved with real-time scaling onsite. A set of compound diagnostic system is developed for the large area laser beam intensity distribution measurement, which is mainly composed of 256 calorimetric detectors, 120 photoelectric detectors, multi-channel data sampling module and one central processing computer. The total energy of the laser beam is accurately measured with calorimetric detectors, and the spatial intensity distribution with high temporal resolution is given by the photoelectric detectors. With the merits of energy accuracy and the temporal resolution based on the two kinds of detector units, the compound diagnostic system can be used to measure accurately the far-field temporal and spatial distribution of high energy laser beams.

The design and performance of a closed cycle, repetitively pulsed HF laser is described. The homogeneous glow discharge is formed with UV pre-ionization and transverse discharge structure. The optimal output parameters of single pulse operation are given by the investigation of discharge characteristics in SF₆ /C₂H₆ gas mixture and output characteristics of laser pulse. The repetitively pulse energy stability of laser device are checked with different conditions of gas flowing velocity, charging voltage and total pressure of gas mixture. It is shown that the maximal output energy of laser pulse of 0.6J, peak power 3MW are obtained. Total efficiency of laser device is about 2.4%. When the gas mixture circulating with 4m/s flowing velocity, the maximal running frequency of 50Hz are obtained and operating stability keep well. Under these conditions, the laser pulse energy keeps stable and the average output power is 18W.

High average power pulsed TEA CO₂ lasers have many important applications, such as laser manufacturing, military applications, but there rarely have reports about the theoretical and experimental studies on the virtual confocus resonator of pulsed TEA CO₂ laser, especially its far field optical quality. Based on the real date of the unstable resonator modified by the stable resonator of high power TEA CO₂, three common theoretical evaluations and analyzes were conducted and compared with the measured results of far field light intensity distribution with 2 kW designed unstable resonator laser with the block ratio is ε=0.404. The results show that the unstable resonator can obtain near diffraction limitation and high optical quality beam. The β factor is smaller than 4 times than the stable resonator. Furthermore, the smaller block factor can make higher power in bucket for the unstable resonator. The comprehensive prediction and evaluation of designed unstable resonator need to synthetically use these three theoretical methods of the evaluations. The simulation results, with considering the optical aberration, heat distortion and atmospheric effect, agree well with the real recording image by the infrared imaging system in the distance of 300m. The research of this paper has very important reference value for evaluating the tactical effectiveness and optimization design of high power TEA CO₂ laser system with different unstable resonators.

The characteristics of Delano diagram are especially helpful in instrumental systems type with considerably separated components. For high power excimer laser system, especially for image relay scheme, the Delano diagram method is highly advantageous for the system’s thin lens layout design. A primitive experimental image relay and it’s combination optical layout is investigated in our high power XeCl laser system, with intensity smoothed spatial incoherent source. Instead of the uniform intensity distribution on the target as expected, it is obvious shows in the final image on the target that a gauss like intensity profile and a large amount of astigmatism results. There are two possible reasons: the first one is that not keeping proper relay of pupil plane (or Fourier plane) in the final stage, simply care the collimated beam of virtual object in the final focusing stage. With the help of Delano diagram, it’s clearly shown in the diagram that the Fourier plane and the image plane come very close, indicates that a complete image relay of the object plane and Fourier plane is needed. The second reason is due to the off-axis setup in the large aperture main amplifier, which introduce significant astigmatism aberrations in the final optical path. This question can be solved using proper tilt and de-center of reflective mirror pair setup, and two possible such combination pairs are proposed.

This paper presents the results of studies on high power photochemical XeF(C-A) laser with repetition mode. A new design of optical pumping source is proposed and the deposition efficiency is higher than 75 %. The form process and the temporal and spatial characteristics of the XeF₂ photodissociation wave are studied experimentally. The results indicate that when the deposition power is 12.5 MW/cm, the maximum brightness temperature reaches more than 25 kK and the photon flux obtained more than 4×10²³ photon s^-1 cm^-2 in the VUV range of 130 nm~180 nm. A novel XeF(C-A) laser which can be operated in repetition mode has been developed based on surface discharge optical pumping technique. The ideal output energy results of 20 laser pulses are presented under different repetitive rates and their optimal experimental conditions. Output energies of more than 4J and better stability can be obtained when the laser device operates at 1, 2 and 5 Hz, respectively. When the gas feed rate is larger than 53L/s, the average energy of 20 laser pulses is up to 3.2J at the repetitive rate of 10Hz. The technology for the laser spectral narrowing is studied.

In high power eximer laser system, amplified spontaneous emission (ASE) decreases the signal contrast ratio severely, leads to waveform broadening and distortion, and impacts on accurate physical experiments. In this article, based on principle of short pulse generation by electro-optical (E-O) switch, a method for ASE suppression of laser amplifiers chain was established. A series of studies on UV electro-optical switches were carried out, and electro-optical (E-O) switches with high extinction ratio were developed. In the waveform clipping experiments of the first pre-amplifier, the extinction ratio of the single and cascaded dual E-O switch reaches 10³ and 10⁴ order of magnitude, the laser pulse signal contrast ratio was promoted to 10⁵ and 10⁶ level, respectively. In the experiments of single channel MOPA (Master Oscillator Power Amplifier system), the cascaded dual E-O switch was adopted to suppress ASE of the whole system, and a fine narrow pulse was obtained on the target surface, which gives out one effective solution to the problem of waveform amplification of the high power eximer laser system.

A kind of beam automatic alignment method used for double paths amplification in the electron pumped excimer laser system is demonstrated. In this way, the beams from the amplifiers can be transferred along the designated direction and accordingly irradiate on the target with high stabilization and accuracy. However, owing to nonexistence of natural alignment references in excimer laser amplifiers, two cross-hairs structure is used to align the beams. Here, one crosshair put into the input beam is regarded as the near-field reference while the other put into output beam is regarded as the far-field reference. The two cross-hairs are transmitted onto Charge Coupled Devices (CCD) by image-relaying structures separately. The errors between intersection points of two cross-talk images and centroid coordinates of actual beam are recorded automatically and sent to closed loop feedback control mechanism. Negative feedback keeps running until preset accuracy is reached. On the basis of above-mentioned design, the alignment optical path is built and the software is compiled, whereafter the experiment of double paths automatic alignment in electron pumped excimer laser amplifier is carried through. Meanwhile, the related influencing factors and the alignment precision are analyzed. Experimental results indicate that the alignment system can achieve the aiming direction of automatic aligning beams in short time. The analysis shows that the accuracy of alignment system is 0.63μrad and the beam maximum restoration error is 13.75μm. Furthermore, the bigger distance between the two cross-hairs, the higher precision of the system is. Therefore, the automatic alignment system has been used in angular multiplexing excimer Main Oscillation Power Amplification (MOPA) system and can satisfy the requirement of beam alignment precision on the whole.

An optical parameter oscillator base on KTP nonlinear optical crystals and a frequency doubling Nd:YAG lase was built. The wavelength of the signal light could be tuned from 750-800nm. At the wavelength of 780.2nm it could provide 62mJ each pulse with duration of 14 ns and spectrum (FWHM) about 0.4nm, and at the wavelength of 755nm the energy of each pulse was 10mJ with duration of 8ns. When the signal passed through a 10cm long Rb cell with Ar buffer gas at the temperature of 120°C and the wavelength was tuned from 779nm to 781nm, it could be observed that the fluorescence in the cell changed from dim to clear at first and then declined. Fluorescence could also be observed when the signal wavelength was 755nm and the cell was heated to 180℃. Which indicated that this OPO can provides over 1MW peak power for the research of rubidium lasers and rubidium-rare gas excimer lasers.

We propose a continuous wave (CW) middle infrared (MIR) and long infrared (LIR) dual-band laser based on energy transferring from DF (v) to CO₂(00⁰0). A total output power of 5W is achieved by the proposed dual-band laser consisted of DF gain medium module (DF module) and DF-CO₂ gain medium module (DF-CO₂ module). Technologies about the gain peak position, beam qualification are analyzed. The two modules use a common stable resonator and output mirror with nominal transmissivities of 3.5%-5% in the MIR band and 6%-10% in the LIR band. Spectra of dual-band laser are acquired.

In this paper, we demonstrate the high power diode-side-pumped Nd:YAG laser on the low gain three lines at 1112, 1116 and 1123 nm. By special coating design or inserting etalon in the cavity, the single wavelength oscillation can be achieved with high output power either in continuous-wave (CW) mode or in actively Q-switched (QS) mode. With special coating design, the maximum CW output power at 1123 nm can be up to 219.3 W. By tuning the tilt angle of an etalon in the cavity, the highest output powers at 1112, 1116 and 1123 nm were obtained to be 72, 43 and 63 W operated in QS mode, and 75, 47 and 71W in CW mode, respectively. This compact laser system, which is capable of selectively operation at one of the three lines at 1112, 1116 and 1123 nm, is of important practical value. The high power achievable with the present laser may enable some interesting applications, such as chemistry, differential absorption lidar, second harmonic generation (SHG) into visible and fourth harmonic generation (FHG) into ultraviolet lasers.

We propose a new idea to measure the temporal contrast of laser pulses in this paper. Unlike the traditional time-to-space transformation method, the design in this paper can be called a somewhat time-to-time transformation. A single-shot pulse beam is simultaneously divided into two separate beams by a beam splitter. The two beams then enter a pair of optical replicators respectively to generate two pulse sequences that have equal time intervals respectively. The time interval of the two sequences alters by about 100fs that we can use one sequence to scan the other at a time resolution of 100fs through a nonlinear crystal. The time resolution depends on the altering of time interval and the time window depends on the pulse number of the sequence. This method can avoid the spatial modulation of the laser pulse. On the other side, the time resolution and time window are adjustable. It is also possible to measure the high contrast with a low-dynamic- range detector by attenuating the power of each pulse in the sequence respectively.

A set of ~450 noncentrosymmetric sulfides has been observed in reference to nonlinear optical properties. It has been found that on the plane of the oxide bond lengths the noncentrosymmetric sulfide crystals are dominantly positioned into a rosette of two intersected ellipses of «acentricity». The strongly non-monotonic dependency of nonlinear optical susceptibility χ⁽²⁾ on the shortest chemical bond length L(E,M-S) has been obtained for sulfides. The suggested crystal chemistry analysis is useful for searching new noncentrosymmetric sulfide crystals.

We report on a nanosecond master oscillator /power amplifier architecture for optical parametric conversion of high pulse energy from 1.064μm to 1.572 μm in KTiOAsO4 crystal. The signal emission is amplified by two different parametric amplifier architectures respectively. By comparing the results obtained, a novel amplifier architecture is chosen which is expected to combine the high gain and good beam quality. With a seeding signal energy of 1 mJ, and 400mJ pump pulse at 100Hz, a gain up to 64 at 1.57μm with the beam quality M² less than 4.8 is realized. The total optical-optical conversion efficiency reached 16%.

A compact passively Q-switched and mode-locked erbium-doped fiber laser based on graphene saturable absorber was reported in this paper. A fiber ferrule, which had graphene deposited on the core region, was used as the saturable absorber. The Q-switched operation was initiated with a low pump threshold of about 50 mW at 974 nm and the repetition rate can be widely tuned from 14 kHz to 70 kHz along with the increase of the pump power. Moreover, the mode-locking state working at 1559.7 nm with a 0.4nm spectral bandwidth and about 3 ns pulse duration was also demonstrated in the same ring cavity when the pump power increased to about 150 mW. This is, to the best of our knowledge, the first report of the fiber laser, which had the both Q-switched operation with so wide repetition rate and mode-locking operation in the same ring cavity based on the same graphene saturable absorber.

The modified Bridgman method with heat field rotation was used to grow ε-polytype single crystals of pure and 1, 2 and 10 mass % S-doped GaSe or solid solution crystals GaSe_1-xS_x, x = 0.002, 0.091, 0.412. The interaction of ultrashort laser pulses of ∼ 100 fs duration at 800 nm and 2 μm with the grown crystals was studied at room temperature. Up to 3.4-fold advantage of S-doped crystals in limit pump intensity (no decrease in the transmission) was found under 800 nm pump at S-content increase up to 10 mass %. The advantage became a half less at 2 μm pump due to a decrease of two-photon absorption in pure GaSe crystals. The spectral dependence of transient absorption is recorded with 37 fs resolution and interpreted. It was ascertained that first observable damage of high quality crystals is caused by dissociation of submicrometer thick surface layer to initial elements and do not influence the frequency conversion efficiency until alloying of dissociated Ga. Local microdefects, multiphoton absorption and transient transmission processes are identified as key factors responsible for damage threshold.

The theoretical analysis and experimental research of the optical parametric oscillator (OPO) based on periodically poled LiNbO₃ (PPLN) crystal are presented. The wavelength tuning curves of PPLN-OPO are calculated through the coupling equations of the three-wave mixing. An optical parametric oscillator with the output signal at 1.49μm and idler at 3.8μm, which is pumped by a Nd:YAG laser at 1.064μm, is obtained based on PPLN of length 20mm and thickness 0.5mm. When the pump power of the Nd:YAG laser is 5.2W with a repetition rate of 5kHz, the output of the idler at 3.8μm reaches 307mW.

A chalcogenide glass was used for an optical Kerr gate to sampling pulse contrast of femtosecond lasers with low repetition rate ( 40 Hz). The dynamic range of this method reached 10³, with a scanning range of 150ps and temporal sampling rate of 6.3 fs. The advantage of this method lies in its broad spectrum range including visible and NIR spectral region and easy operation.

The demands of the industry are cheap and fast production of highly sophisticated parts without compromises in product quality. To realize this requirement, we have developed a laser guided and stabilized gas metal arc process (LGS-GMA welding). The new welding process is based on a gas metal arc process using low power laser radiation for stabilization. The laser stabilization of gas metal arcs welding is applied to joint welding and cladding. With only 400 W laser power and a focal spot of 1.6 mm the laser radiation is mainly interacting with the arc plasma in order to guide and stabilize it. In joint welding up to 100% increase in welding speed is possible, at equal penetration depth. The guidance effect also enables the process to weld in challenging situations like different sheet thicknesses. Used for cladding, the enhanced process stability allows low penetration depth with dilutions of only 3%. Coatings with up to 63 HRC were achieved.

Short und ultrashort pulse UV laser processing of solid surfaces with sub-micron precision is demonstrated. The combination of a short laser wavelength providing strong absorption and high optical resolution and a short pulse duration minimizing heat affected zones enables ultra precise patterns on any solid material. High speed is achieved using parallel processing. Periodic patterns are fabricated utilizing various optimized beam delivery concepts like multilevel diffractive optical elements, phase controlled interference, proximity phase mask method, and two grating interferometer. The respective advantages and the fields of application are discussed.

A two dimensional model is developed to simulate the process of keyhole formation on aluminum slab during laser drilling by millisecond pulsed laser. In this model, phase change, including melt and vaporization, is considered by not only introducing the equivalent specific heat capacity but also explicitly adding the source terms of gas dynamics in the thermal-hydrodynamic equations and level-set equation firstly. Besides, in order to trace the free surface, a modified level-set method is developed. All possible effects which can impact the dynamic behavior of the keyhole are taken into account, containing gravity, recoil pressure of the metallic vapor, surface tension, and Marangoni effect. This simulation is based on the same experiment condition where 1064nm Nd:YAG single pulsed laser with 3ms pulse width, 18J peak energy and 300μm spot radius is used. The results of the keyhole morphology and the melt ejection trajectory angle are in good agreement with experiment results, indicating the model is reasonable and feasible.

Many nonmetal film products, such as herbal plaster, medical adhesive tape and farm plastic film, require drilling dense small holes to enhance the permeability without affecting the appearance. For many medium and small enterprises, a low-cost, high-speed laser drilling machine with the ability of processing different kinds of nonmetal material is highly demanded. In this paper, we proposed a general purpose high-speed laser drilling method for micro-hole production on thin nonmetal film. The system utilizes a rotating polygonal mirror to perform high-speed laser scan, which is simpler and more efficient than the oscillating mirror scan. In this system, an array of closepacked paraboloid mirrors is mounted on the laser scan track to focus the high-power laser onto the material sheet, which could produce up to twenty holes in a single scan. The design of laser scan and focusing optics is optimized to obtain the best holes’ quality, and the mirrors can be flexibly adjusted to get different drilling parameters. The use of rotating polygonal mirror scan and close-packed mirror array focusing greatly improves the drilling productivity to enable the machine producing thirty thousand holes per minute. With proper design, the hold uniformity can also get improved. In this paper, the detailed optical and mechanical design is illustrated, the high-speed laser drilling principle is introduced and the preliminary experimental results are presented.

Long-period fiber gratings (LPFGs) have found wide applications in optical communications and smart sensing. Among the various methods for fabrication of LPFGs, infrared femtosecond laser writing is one of the most attractive methods in terms of flexibility, being applicable to both photo sensitive and insensitive fibers, and no needs for any pre-designed masks. Although fabricating LPFGs by infrared femtosecond laser has been demonstrated for more than ten years, the reported maximum rejection band depth of LPFGs fabricated with this method for standard telecommunication fiber (SMF-28) without hydrogen loading is no more than 10 dB, and in the meanwhile its out-of-band loss is rather high. In this report, LPFGs with major resonant attenuation over -16 dB near 1300 nm are produced in standard single mode fibers with two dimension visional femtosecond laser manufacturing system. The contrast of the resonant rejection band resulting from core-cladding mode coupling can be significantly increased by applying a proper amount of axial stress along fiber during laser writing. With higher laser energy irradiation, LPFGs of multiresonance peaks plus larger out-of-band loss are frequently made. Such out-of-band loss is mainly caused by Mie scattering, and it can be restrained by properly selecting grating duty cycle.

Diode pumped alkali vapor lasers (DPAL) is a rising high-energy laser. The wavelength of which is consistent with the response curve peak position of solar cell, and it has broad application prospects in laser directed energy transfer. The paper bases on the application of solar unmanned aerial vehicle (UAV) energy transfer in high altitude and longendurance conditions. For the first time by using the MODTRAN and FASCODE, we calculate the transmittance of Potassium, rubidium, cesium laser in the typical atmospheric conditions vertically and different angles of atmospheric slant path by the numbers, The result shows that DPAL has a very high atmospheric transmittance, and also a valuable reference in other applications with the atmospheric transmission.

Laser shock peening can significantly improve the fatigue life of metals by introducing plastic deformation and compressive residual stresses near the surface. It has been widely applied on metals for surface strengthening. The plastic deformation behavior of brittle materials such as single crystal silicon under LSP is rarely studied. In the present research, the surface integrity and residual compressive stress of P-type single crystal silicon in <100< orientation shocked by LSP at imposed high temperature were measured to investigate the plastic deformation mechanism at high temperature and high compressive stress. The surface morphology of shocked silicon, observed using optical microscopy, showed that the cracks on the shocked silicon surface became less and the fragments were smaller while the temperature or the laser power density increased, which indicates that the plasticity of single crystal silicon is improved at high stress and temperature. However, the excessive laser power density would lead to local damage of the shocked silicon. The residual stress, measured using Raman scattering method, showed that the compressive residual stresses with magnitude of a few hundreds of MPa were introduced in the surface layer of silicon after LSP at imposed high temperature, and it increased with respect to the temperature and the laser power density. The experimental result indicates the material has experienced the plastic deformation and provides a potential processing method to improve the mechanical behavior of brittle material like single crystal silicon.