This PDF file contains the front matter associated with SPIE Proceedings Volume 6823, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We designed a new solid-state laser with the construction of radial slab array. Three kinds of gain distributions are considered according to different pumping structure. The numerical calculated results show that this kind of laser can output high beam quality laser both coherent and incoherent conditions. It is prospective to be a new research direction for high power, high beam quality, compact and scalable solid laser.

Thermal lensing in an end-pumped Tm,Ho:YLF laser crystal has been investigated with a theoretical model of continuous-wave (CW) quasi-three-level laser. Under considering energy transfer up-conversion (ETU) and ground state re-absorption (GSA), the rate equations are given. The influence of ETU on fractional thermal loading is calculated, and the results show that fractional thermal loading critically depends on the pump-to-mode size ratio. The temperature distributions of a Tm,Ho:YLF crystal under different pump powers have been analyzed. The output power and the focal length of the thermal lens as a function of pump power are obtained in experiment. The experimental results are compared with theoretical results, and the experimental results show that the theoretical results are reasonable.

A petawatt laser facility with three beams for fast ignition research and strong-field physics applications has been designed and is being constructed. The first beam (referred as SILEX-I) is a Ti:sapphire femto-second laser which pulse width is 30 fs, and till now, output power has reached to 330 TW. The other two beams are Nd³⁺:glass lasers which output energy are larger than 1kJ and pulse width are about 1ps and 1ns respectively. By using the technology of OPA pumped by 800nm femtosecond laser and seeded by super-continuum spectrum white light, the three beams are synchronized with each other without jitter time. By using the seeds from OPA pumped by femtosecond laser, and by using the pre-amplification stage of OPCPA, the signal to noise ratio of the Nd³⁺:glass petawatt laser will reach to 10⁸. Active methods are taken to control the gain narrowing effect of the Nd³⁺:glass amplifiers, giving the option to compress the chirped pulse to ultrashort pulse with width less than 400fs. Tiled multilayer dielectric coating gratings are used for the compressor of the PW beam, which has been successfully demonstrated on a 100J picosecond Nd³⁺:glass laser system.

The theoretical solution to the absorbed pump light inside a laser medium is presented. It is shown that the pump light absorbed with respect to the transport distance is not simply an exponential function. When the pump intensities go high enough, their relation becomes a nonexponential function. These theoretical results have been applied to YAG:Nd, and the regularity of pump light intensity variation inside a laser medium is indicated. We experimented with YAG:Nd, and the experimental result is in agreement with the theoretical result.

The coupling technique of high-power semiconductor laser array is an advancing key project. A high power density collimated beam, which facula is much smaller, can be get by coupling high-power laser array with selfoc lens array. At the same time, the coupling efficiency is higher. The factors which affect the coupling efficiency mainly include NA, diameter, length and end surface fabricating of selfoc lens and coupling technique. In this paper, an 1×19 linear laser array which maximum continuous output power is 22W is coupled with a corresponding selfoc lens array. The maximum coupling efficiency is 58.2%.

The geometry of ytterbium-doped active media in diode-pumped lasers can be calculated with the help of numerical modeling for the optimization of high-energy and repetitively pulse amplifiers. In the first step the optimum thickness of the longitudinally pumped gain medium of Yb:YAG is obtained with a theory of quasi-three level laser ions. For the parameters of the amplifier which will deliver a 100 J, 10 Hz, 10 ns pulse, the optimum thicknesses is 5.5mm with a doping concentration of 3.92*10²⁰ cm^-3 taking the amplified spontaneous emission (ASE) into account. In the second step, we analyze the laser performance of the amplifiers by using various cooling configurations. The cooling configurations investigated here include those both by forced convection cooling in a narrow passage. In every case we determine the temperature rise, the longitudinal and radial temperature gradient, and the resulting energy storage and extraction efficiency. The simulation results show that, with a pumping intensity of 20 kW/cm² at 10 Hz and a doping concentration of 3.92*10²⁰ cm^-3 at a thickness of 5.5 mm thick piece Yb:YAG, for a laser injection fluence of 0.2 J/cm² (10 ns) ,the output laser fluence and optical-to-optical efficiency are expected to be 7.2 J/cm² and 35%, respectively, at a heat exchange coefficient of 1 W/cm²/K of water and 250 W/m²/K of gas.

A tunable hybrid Brillouin-Raman fiber laser system with simple structure is proposed. With a tunable ECL laser whose power is 3dBm used as Brillouin pump, a fiber Raman laser whose maximum output is 1200 mW used as Raman pump, and 25km DSF fiber used as both Brillouin and Raman gain media, an Brillouin-Raman fiber laser with tunable range more than 40 (1530-1570 nm) nm was demonstrated. Multi-frequency Stokes lines at an average of 10GHz frequency spacing was observed across the tuning range. When the wavelength of Brillouin pump is in the range of 1550nm to 1565 nm, more than 10 stokes lines were observed. The Brillouin fiber laser has the potential of simpler configuration, wider tunable range and more wavelengths when compared with Brillouin-Erbium fiber laser.

We propose a kind of photonic crystal fiber with flat-top fundamental mode by introducing a depressed central dip into the core of the conventional index-guiding photonic crystal fiber. The design guidelines and characteristics of the large flattened mode photonic crystal fiber (LFM-PCF) are discussed in detail. By appropriate design, the effective area of the LFM-PCF can be increased by a factor of greater than 2 as compared with conventional index-guiding photonic crystal fiber with the same hole and pitch parameters. The improved effective area, single mode operation and flat-top fundamental mode output make LFM-PCF an ideal candidate to realize high power, high beam quality fiber amplifiers and lasers.

It is common to use Yb-doped double-clad fibers as gain medium of high power fiber lasers. These fibers are similar to the so-called "un-doped" telecommunication fiber. Because of small core size, only from several microns to tens of microns, there are easier causing self-pulsing affects in the fiber lasers. In the first part it is reported the several kinds of self-pulsing according to the reported papers, like relaxed oscillation, saturated absorption effect, stimulated Brillouin scattering and stimulated Raman scattering. Then it is presented the experimental study and the different self-pulsing phenomena. The result shows that under the high power condition, although ytterbium ions without concentration effect, but large core Yb-doped double-clad fiber are the same to three-level ion systems that self-pulsing behavior was the result of relaxed oscillation. To Yb-doped fiber laser, saturated absorption effect, stimulated Brillouin scattering and stimulated Raman scattering cannot be ignored.

Self-organized coherent laser array seems to be a promising method for coherent combining fiber lasers. Phase locking is realized by mutual energy injection, without any active phase stabilization, requirement of the fiber length or the output power for individual lasers. In this paper, rate equations describing time evolution of the complex, slow varying electric field and gain of an array of single transverse and longitudinal mode lasers proposed in former literature was referred to for modeling the self-organized fiber laser array. The process for phase-locking evolution of each individual laser in a fiber laser array was modeled and analyzed theoretically and numerically. For the case of an array containing 2 or more than 4 lasers, the array will be in an out-of-phase mode, with a phase difference of π between adjacent laser output modes. For an array containing 3 lasers, phase difference between adjacent lasers would be ±2π/3. We will cite experiments to validate our verdict. We can also obtain by investigating on the model that more powers can be extracted than the summation individual free running lasers. Those phenomenons have been reported but not explained. At the end of this paper, we perform system level analysis on the fiber laser array numerically. We find that with the number of lasers increasing, the array will have a more critical condition on detuning frequency for phase locking.

The feasibility of realizing beam cleanup of high power lasers using stochastic parallel gradient descent (SPGD) wavefront control method has been demonstrated numerically. The numerical model of an adaptive optics system comprising a 44-element deformable mirror and a far-field system performance metric sensor is first setup which operates with the SPGD wavefront control method. The system is then used to correct for the dynamic aberrations of a laser beam where the phase screens of the beam are constructed from the simulation data of a high power laser system and are introduced into the light wave time sequentially according to the iteration rate of the SPGD wavefront controller. The correction results show that the beam cleanup system investigated here can effectively compensate for the dynamic aberrations of the laser beam involved.

In an inertial confinement fusion (ICF) system, wave-front aberrations existed in laser beam will enlarge the focal spot size and decrease power density at the target. Fortunately, an adaptive optical system (AO) could be employed in ICF system to correct the beam aberrations. As a powerful wave-front detector, Hartmann-Shack (H-S) sensor is often utilized as a wave-front sensor in AO. However, H-S sensor can not detect the aberrations after the sampling location. A new method is presented to measure the aberrations of entire ICF beam path in this paper. Based on the AO, a CCD is installed in the target chamber to detect the focal spot distribution. The deformable mirror's (DM) is yielded to different surface shapes; the extra different aberrations are modulated and added to ICF beam path, and then create their corresponding focal spots. The extra aberrations and the corresponding focal spots intensity could be recorded simultaneously by H-S sensor and CCD respectively. An amendatory phase-retrieval algorithm which is introduced can reconstruct the aberrations of entire ICF beam path from the pairs of extra aberrations and their corresponding focal spots intensity. The numerical simulation show that the AO can correct the aberrations of entire beam path of ICF successfully based on this method.

The method of real ray trace for the time characteristic analyzing of laser pulse is presented. By tracing the sampling rays with optical path or phase initialized by given input pulse and limited by the entrance pupil, the output pulse samples are calculated including the pulse width and energy distribution and the fitting pulse curve is obtained. Further more, this method can be also used for analyzing the affection of the tolerance in pulse transmission systems to the beam quality. Taking some pulse transmission systems as examples in which there are different diffraction components such as diffraction gratings, binary optical elements and holographic elements, the output pulse curves come from different input pulse are given, and the functions of different diffraction elements as pulse boarder and compressor are compared. As shown by the results that the multiple diffraction of binary optical elements will not only generates multiple focus points at the output space to affect the space quality of laser beam, but also leads to broad the pulse width so as to change the laser's time characteristics.

Two kinds of novel spatial filters constructed by metamaterials and their possible applications in high-power laser systems have been investigated. The first one can be constructed by forming a compensating bilayer of indefinite metamaterials. It is shown that the cutoff wave vector of the low-pass spatial filter can be adjusted desirably. The second kind of low-pass spatial filter is based on the controllable dispersion characteristics of photonic crystals. With proper design, the higher spatial frequency components, which are incident to the filter with angles exceed a critical value, are reflected totally because no Bloch waves of the photonic crystals can be excited. However, the lower spatial frequency components are coupled to the self-collimating modes and permeate with high transmission. The applications of the two novel kinds of metamaterials-based low-pass spatial filter in high-power lasers are discussed.

Metamaterials (MMs) are artificial structures, which can be engineered to satisfy the prescribed requirements. The most important difference between an ordinary medium and a MM is that the former has a constant permeability, while the latter has a dispersive and controllable permeability. MMs can extend the electromagnetic properties of conventional materials, and the study of the nonlinear propagation of ultrashort pulses in MMs could lead to completely new electronic and optical devices. In this paper, the research advances on the propagation of electromagnetic pulses in MMs with third-order nonlinear response are briefly described. Special effort is focused on the typical nonlinear optical phenomena such as modulation instability, bright and dark solitons.

Diode-pumped alkali vapor laser (DPAL) is a new class of laser, and it is expected to realize high efficiency and high-average-power laser with good beam quality (near-diffraction-limited). DPAL offers CW laser radiation at near-infrared wavelengths and can find a lot of applications in power beaming, drilling oil and gas well and laser material processing. Operating temperature affects not only the density of alkali vapor atom in active region, but collision broadening and fine-structure mixing rate. In this paper, we study the operating temperature characteristics of DPAL. Based on the theory of quasi-three level CW laser, the dependence of cesium laser output power on the operating temperature has been simulated. The results showed that there exists an optimal operating temperature around 95 to 110 centigrade for high pumping power. In lower temperature region, the laser power rise linearly with increasing operating temperature, namely increasing active density. However, the laser power falls after the optimal operating temperature, because the spontaneous radiations deplete large numbers of stimulated population contributing to laser emissions. At the optimal temperature, an optical- optical efficiency of about 73% is able to reach theoretically.

The studies on large aperture volume discharge of TEA (transversely excited atmospheric) CO₂ laser are reported. To obtain stable and uniform large aperture volume discharge, the effects of electrode profiles, preionization methods and parameters of discharge circuit have been studied experimentally. For a discharge construction with 70 mm gap and pumped by a 3-stage Marx high voltage pulse generator circuit isolated by resistance with 0.5 μF capacitance each stage, 150 J pulse energy was obtained from a discharge volume about 4 l.

A theoretical model is established to describe the α-RF discharge in slab Oxygen Iodine lasers, according to the continuity equation of electron density, the electron energy equilibrium equation and the continuity equation of current density. Assuming a Maxwellian energy distribution, the spatial distributions of electron density and electric field in RF plasma are obtained by numerical method. The effects of parameters on discharge characteristics have been analyzed. The results show that the current density has a big effect on the electron density in discharge area. The influences of excitation frequency on the maximum value of electric field and the thickness of boundary layer are also discussed. And the spatial distributions of electron energy and excitation efficiency of singlet delta oxygen have been calculated. The influences of gas mixture on the excitation efficiency of singlet delta oxygen are discussed. It provides references of parameters for slab discharge in singlet delta oxygen generating.

A theoretical study of electron trajectories and gain in a quadrupole wiggler free-electron laser (FEL) with ion-channel guiding is presented. The relativistic equation of motion for a single electron in the combined quadrupole magnetic and ion-channel electrostatic fields is solved for the steady-state electron velocity components. Next the electromagnetic radiation copropagating with the electron beam in the FEL interaction region is analyzed and an equation for gain in the low-gain-per-pass limit is then derived. The results of a numerical study of electron trajectories and gain in the presence of the ion-channel guiding is presented and discussed. It is shown that all orbits of group I are unstable, while group II have stable orbits as well as unstable orbits. Effects of ion-channel guiding on the gain are then investigated and shown that gain enhancement is obtained due to the ion-channel guiding.

When terahertz radiation irradiate to the surface of metal sub-wavelength holes array, there will be transmission peak at some frequency because of the surface plasmon resonant. This is the property of selecting transmission of metal sub-wavelength holes array. Many factors affect this property, such as the lattice constant of the array, dielectric of the medium, the thickness of the medium and so on. We mainly discuss the influence of the frequency and intensity of the transmission peak by the thickness of the medium. When the medium film is attached to both sides of the array, we found the changing of the thickness of the medium affect the frequency and intensity of the transmission peak: When the thickness of the medium is increasing, the frequency of the transmission peak becomes lower and the intensity decreases. We also found that when the film is thin (for example 54μm), the intensity of the transmission peak is greater than that of no medium film. This phenomenon shows that attaching thin film to both sides of the holes array will enhance the selecting transmission property.

Based on pulsed laser propulsion, a set of system to measure pulse thrust with repeated loading was established. In the experiment, signals of pulse thrust are transformed into electric signals by PVDF (polyvinylidene fluoride) sensor. Then the electric signals were collected and displayed with data acquisition facility based on PCI controller. With the laser pulse rate of 10 Hz and pulse energy of 80J, the measurement was carried out. Two effective signals of pulse thrust were obtained. Experimental datum show that trend of variation of the first pulse thrust corresponds with that of the second one. The impulse coupling coefficient from the computation and measurements agree well, which indicates that the experimental set is reliable.

Specific impulse is one of the most important parameters of the micro-laser plasma thruster. Based on analyzing the method of measuring specific impulse world widely, a kind of method of measuring specific impulse of the micro-laser plasma thruster is established, in which impulse is got by laser interferometry and ablative mass is got by simulating the photograph of ablative target as a truncated cone. The experimental setup of laser interferometry is introduced and the work principle is given in detail. The method of simulating the ablative mass is supplied and the process is illustrated. Typical experiment is carried out. The research efforts play a certain important role in measuring specific impulse of the micro-laser plasma thruster.

We demonstrate strong optical bistability in 2μm continuous wave Tm,Ho:YLF laser pumped by a 792nm laser diode near room temperature. The bistable region is as much as 100mW wide at 283K and can be controlled by the temperature of the laser crystal. The influence of crystal temperature on the characteristics of optical bistability is obtained. The influence of the pump-to-mode ratio on the bistable characteristics of the laser is also discussed.

We demonstrate a passively mode-locked all fiber ring laser based on all-solid Yb-doped Photonic Bandgap fiber (AS-Yb- PBGF) which is designed to simultaneously provide laser gain and anomalous dispersion. The laser is comprised of 0.42m AS-Yb-PBGF and a segment of single mode fiber (SMF). By varying the length of the SMF from 0.8m to 3.2m, three operation schemes, namely soliton operation, gain-guided soliton operation, and self-similarity operation, have been obtained by means of numerical simulations in split-step Fourier method in the ring laser. In the case of net anomalous cavity group-velocity dispersion (GVD) when the SMF is 0.8m, we obtain soliton pulse with the balance between the nonlinear self-phase modulation (SPM) and the anomalous GVD. The soliton pulse has the pulse duration of 355fs and the bandwidth of 1.9nm, corresponding to the time-bandwidth product of 0.33, nearly a transform-limited pulse. As the length of the SMF is changed to 2m, self-similar propagation is generated with the net cavity GVD of +0.014ps². The pulse has strong frequency chirp and high pulse energy up to 4nJ. The pulse duration is 2.5ps with the bandwidth of 2.1THz. To obtain gain-guided soliton, we change the SMF to 3.2m leading to a large net positive cavity GVD of +0.04 ps² and enforce the spectral limit of the gain fiber. A chirped gain-guided soliton pulse is observed with pulse energy of ~1nJ, the pulse duration of 2.5ps and the bandwidth of 2.5 THz.

This paper presents some results on the air-breathing propulsion experiments with a parabolic light craft and a self-made UV-preionized TEA CO₂ laser with 115 J maximum pulse energy. In wire-guided vertical flight experiment, impulse-coupling coefficient 390 N/MW is obtained at the pulse energy 60 J. The influence of the shape of the lightcraft and the laser pulse profile on the coupling coefficient was discussed. The spectrum of the plasma was detected using monochromator, and the time evolvement process of line spectrum of the plasma was analyzed.

The authors report stable short high-repetition-rate Q-switched pulses in acousto-optic Q-switched ytterbium-doped double-clad fiber lasers. This device uses a diode pumped at 975 nm to end pump the large mode area double-clad fiber laser. In the experiment acousto-optic modulator is used as a special Q-switching in the F-P cavity. As a result, sub 100 nanosecond pulses are obtained with varying the acoustic-optic repetition rate from 1 kHz to 100 kHz. The Q-switching technique provides a novel method to generate short pulses at high repetition rate.

The phenomenon of hot image in high power lasers is closely related to the spatial uniformity of laser beams and the running safety of laser systems. Here we study the formation of the second-order hot image of phase defect in the high-power broadband laser system, special attention is payed to the role of bandwidth of incident beam in the formation of the second-order hot image. It is shown that, as the laser bandwidth increases by either increasing the positive temporal chirp or reducing the pulse duration the intensity of the second-order hot image decreases. However, as the amount of negative chirp increases, the intensity of the second-order hot image increases first but decreases after reaching a maximum value. The distance between the second-order hot image and the nonlinear medium is found to be about half that between the phase defect and the nonlinear medium. The influence of phase shift caused by the phase defect and nonlinear effect on the formation of the second-order hot image is also numerically studied.

The study of thermal effect plays an important role in the research and application of high power heat capacity laser. FEM has been used to seek the numerical solution of heat conduction equation in the past study of laser thermal effect, but the method can't describe the infection of laser material characteristic and pumping laser on the temperature distributing and thermal stress distributing. And it is difficult to analyze the thermal lens effect, thermal birefringence effect and their influences on the laser beam quality. The 3 dimensions heat conduction model under the cylindrical coordinate is set up on the base of pumped structure of face-pumped disk laser. And the precise solution of transient temperature field distribution is got through resolving the 3 dimensions heat conduction equation using integral-transform method. On the base of this, the thermal stress field transient distribution is worked out. Using a Φ50mm×18mm Nd:GGG disk laser as an example, the temperature distributing and thermal stress distributing under the heat capacity model is calculated. The result and the numerical solution using FEM are a good match, and the theory analyzing result is in accordance with the relative experiment result, so the thermal effect modeling and the resolving method are proved to be correct. The research establishes the base of the further theoretical analysis of thermal effect influence on the laser beam quality.

Based on the angular spectrum theory of light propagation and the mean-field approximation, an expression for intensity of hot image of the intense laser beam through a thick Kerr medium with gain and loss is obtained, beyond the thin-medium approximation. Thereby the dependence of intensity of hot image on the thickness and gain/loss of medium and the property of obscuration are identified analytically and numerically. It is shown that, for a given obscuration, the intensity of hot image decreases as the medium thickness increases for definite B integral and increases monotonously with the medium thickness for definite input power of laser beam. For definite output power of laser beam and gain/loss of medium, the intensity of hot image firstly increases and subsequently decreases as the medium thickness increases. Furthermore, it is shown that hot image from obscuration of phase modulation is more intense than that from obscuration of pure amplitude modulation, even in the presence of medium gain and loss. As the size of obscuration increases, the intensity of hot image first increases gradually, after reaching a maximum value, it decreases rapidly to a minimum value.

Demonstrations of CW lasing in ceramic Cr²⁺:ZnSe are reported. The laser consists of a 1.7-mm thick ceramic Cr²⁺:ZnSe disk pumped by a double-clad Tm-silica fiber laser at 2050 nm. Using a concave HR mirror with a radius of curvature of 500 mm as the rear mirror, the laser delivers up to 1030mW of radiation around 2.367 μm.

To obtain higher pulse energy and pulse peak power of Q-switched fiber lasers, the length of amplifying fiber should be optimized properly. In this paper, the optimum length of fiber for maximum pulse energy or maximum pulse peak power is investigated based on the rate equations of Q-switched fiber lasers. The relationship between the optimum fiber length and the output coupler reflectivity is got by using the mathematical technique of Lagrange multipliers and numerical analysis. As a result, output pulse energy and pulse peak power can be expressed as functions of the fiber length, multiplied by a few simple constants. The results show that, at given pump power level and round-trip parasitic loss, there is a demarcation of output coupler reflectivity which is inversely proportional to the round-trip parasitic loss coefficient. Fiber length should be optimized to achieve maximum pulse energy when the output coupler reflectivity is less than the demarcative reflectivity, and on the contrary, it should be optimized to yield maximum pulse peak power.

Spectral clipping effect in a chirped pulse amplification laser system is developed in this paper. A grating-size-limited stretcher/compressor as well as an amplifier can alter the spectrum profile of an ultrashort pulse, so the temporal profile will be influenced. We present a model of spectral clipping effect and calculate the wavelength-dependent spectral clipping ratios in a CPA laser system for a variety of matched stretcher-compressor designs. Then we analyze the output pulse's temporal distribution, and find that the temporal contrast ratio is mainly determined by the stretcher and the amplifier. The pulse duration of the output pulse is mainly influenced by the amplifier.

High-power lasers are widely used in various scientific, industrial and military applications. There is currently a desire for precision measurement the beam quality of high-power lasers in order to evaluate the performance of the laser systems and the operational effectiveness of chemical and solid-state high-power laser weapons. There are many methods of beam quality determination, such as beam parameter product, encircled energy ratio BQ, Strehi ratio, diffraction limit factor β and beam propagation factor M². In this paper, a beam quality measurement device is developed for high-power lasers. This device consists of a beam attenuator with large reflective ratio and minimal wavefront distortion, an off-axis parabolic mirror, an imaging lens and an infrared focal plane array detector. The laser beam intensity distribution, beam width, beam divergence and beam pointing stability can be obtained in real-time and the beam quality can be evaluated by the various determinations through imaging process. Advantages and disadvantages of these beam quality determination for evaluation the performance of the high-power lasers are analyzed and discussed. The measurement uncertainties of relative parameters are also analyzed and discussed.

Theoretical design optimization of the first-order P-doped fiber Raman laser (FRL) by an explicit approach was investigated. The authors derived an explicit expression for the output power of the laser without using the depleted-pump approximation. The proposed solution shows excellent agreement with numerical simulation. According to the explicit solution, one can clearly know the effects of fiber length, reflectivity of output fiber Bragg grating (FBG), Raman gain and loss of the P-doped fiber and extra losses on the output power. The solution also present a criteria by which one can determine whether the depleted-pump approximation is valid or not. It is very fast and convenient to optimize the output power of the FRL using the proposed explicit solution. The optimal values of fiber length, reflectivity of output FBG and conversion efficiency are obtained under different pump power. While increasing pump power, the optimal fiber length and reflectivity of output FBG decrease and the optimal conversion efficiency increase. There exists a certain tolerance of the optimal parameters, in which the conversion efficiency decreases only slightly. The results provide us an intuitive physical understanding to the laser and are instructive to experimental design of the laser.

Wavelength tunable high power lasers are desired for many applications, such as spectroscopy, sensing and nonlinear optics, etc. A tunable Yb³⁺-doped photonic crystal fiber laser based on a blazed grating in Littrow configuration is demonstrated. The active fiber used in the experiment is a double-clad Yb³⁺-doped PCF which contains an Yb³⁺-doped core of 23 μm in diameter and a holy inner clad of 420 μm in diameter. The laser resonator is composed of a dichroic reflective mirror and a blazed grating which is set in Littrow configuration. To reduce reflection the fiber end near to the grating is polished into an angle of 8 degree. Wavelength tunable output with a range form 1035.425 nm to 1111.770nm is realized. The output power of the laser at different wavelengths is flatten within 0.8 dB. At the available maximum pump power of 12.11 W, the maximum output power of 3.45 W is obtained at 1064.085 nm, which corresponds to a slope efficiency of 35.9%. Degree of polarization of the output at different pump level are all more than 0.87.

Coherent beam combination of fiber laser arrays plays an important role in realizing high power, high radiance fiber laser systems. The stochastic parallel gradient descent (SPGD) algorithm is a newly developed optimization method using the technique of parallel perturbation and stochastic approximation and it is expected that this algorithm can reduce the cost and complexity of a high power fiber laser system when incorporated in its beam combination scheme. In this paper, a numerical simulation model about the fiber laser beam combination system is then established based on beam-quality-metric optimization method. The SPGD algorithm is introduced and used to realize the beam-quality-metric maximization, leading to the maximum output power of the fiber laser system. The results of numerical simulation indicate that the far-field beam intensity optimization method using SPGD algorithm can realize coherent beam combination of fiber laser arrays effectively.

Combining fiber laser beams are of current interest for scaling lasers to high average output power. The Master Oscillator Power Amplifier (MOPA) configuration is important in fiber laser beam combination. The efficiency of coherent beam combining is depended on the phase control precision of the system mostly, which is equivalent to the closed loop output phase noise. In this paper, a simplified negative feedback model of the phase control system is constructed to study the optimum design of the system. The effects of the transfer function of the system on the phase noise of the optical fiber amplifier, the measured noise and the stability of the system are analyzed. The relationship between the closed loop output noise and the system parameters is analyzed and calculated. The results show that there is a set of system parameters to minimize the closed loop output noise for different phase noise of the optical fiber amplifier, and for a fixed set of system parameters, the closed loop output noise of the system almost changes linearly with the change of the input noise. The effective means to achieve optimal system parameters for higher degree of control precision are obtained.

In the paper, a principle is proposed, that is, a high frequency modulated high power CO₂ laser is used as the driving source to heat up the sensor. Using the continual beam and the pulsed beam sent out by the same laser in the same system to carry on the static calibration of the infrared detector and the dynamic calibration of the temperature sensor to be checked, the differences in the environment of the sensor installing and the error caused by the change of thermo physical property can be avoided. Thus the difficult problem of traceable temperature dynamic calibration is solved. Tellurium-cadmium-mercury infrared detector which has good response to the CO₂ laser beam of 10.6μm wavelength is used to measure the surface temperature time (72μs) excited by the CO₂ laser. This dynamic calibration system was used to test the response times of two kinds of thermocouples. The experimental results have shown that this calibration system can be used to calibrate transient surface temperature sensor with a time response of the seconds to sub-milliseconds order and 2000°C. Many thermocouples of company Omega have been tested on the system. The experimental results show that the new calibration method can be used to calibrate surface temperature sensors.

As increasing demand for high power short-pulse laser system for scientific and industrial application, sub-10ns high power pulse fiber lasers attract more and more attentions. In this paper, a hybrid Q-switched Er³⁺/Yb³⁺ co-doped high power fiber laser is presented. The Q-switching in this fiber laser is achieved by combining stimulated Brillouin scattering (SBS) and pulse pumped. On the one hand, through self-Q-switching operation due to SBS in the cavity, the Q-switched fiber laser can produce pulse duration below 10ns. On the other hand, the repetition rate of output optical pulses is dominated by the repetition rate of pumping pulses. With this method, a Q-switched Er³⁺/Yb³⁺ co-doped fiber laser with high power and sub-10ns is obtained. The characteristics of the presented laser have been investigated theoretically and experimentally in detail. The experimental results show that the emitted pulse duration is as short as 4ns, the maximum pulse peak power is greater than 10kW and the repetition rate of output optical pulses can be varied from 0Hz to 5kHz.

A theory for self-fields effects on dispersion relation in a free-electron laser with planar wiggler and ion-channel guiding is presented. An equation is derived for dispersion relation in the presence of the electromagnetic radiation, space-charge wave, ion-channel electrostatic field, and self-fields. Numerical solution of this equation is used to study growth rate. A comparison between the growth rates in the presence and absence of self-fields shows that the growth rate decreases considerably due to the self-fields.

Laser-induced dispersive fluorescence (LIDF) spectrum of NO₂ molecule in the spectral region of 508.3-708.3nm is obtained with the 508.0nm excitation wavelength. It is found that at low sample pressure the spectrum is composed of a banded structure superimposed on a continuous one. While the spectrum show itself as a continuous envelope centered at 630.0nm when the pressure with a higher value. NO₂ molecules are excited to the first excited state A²B₂ by absorbing laser photons. Owing to the strong interaction between X²A₁~A²B₂ and A²B₂ ~ B²B₁states, some excited molecules redistribute to X²A₁ and B²B₁ states by the process of internal energy conversion or quenching. This induces the fluorescence come from different excited states. Based on the experimental data, the vibration frequencies of the ground electronic state of NO₂ molecule are obtained. They are ω₁=(1319±12)cm^-1, ω₂=(759.8±0.7)cm^-1,and ω₃=(1635±29)cm^-1. The optimum-receiving wavelength for detecting NO₂ gas with the technique of LIDF is proposed.

A narrow-linewidth master-oscillator fiber power amplifier system with homemade large-mode-area fiber is demonstrated. Some fundamental characteristics of this system, including the output power characteristics, the emission spectrum characteristics, as well as the confirmation of single-frequency operation are investigated in detail. The system generates up to 7.3 W of single-frequency radiation at a wavelength of 1064 nm with 39% slope efficiency and 26% optical-optical power conversion efficiency.

Optical turbulence effects, such as irradiance scintillation, fluctuation of arrival angle, beam wander, and beam spreading, etc., degrade the beam quality as a laser beam propagates in the turbulent atmosphere. Of these effects, the scintillation is a dominant effect in many applied fields such as high-data-rate laser atmospheric communication, astronomical adaptive optics imaging, and other laser engineering. The scintillated irradiance depends on integral of optical turbulence along the propagation path and it induces a perturbation on the amplitude of the electro-magnetic field. As the integral is smaller, the Rytov weak fluctuation theory can solve the problem successfully. However, with an increase in the strength of the atmosphere turbulence or the path length, multiple scattering events must occur and result in saturation. The irradiance scintillation of laser beam propagation in a slant-path in the boundary-layer is investigated for the cases of weaker to moderate-to-stronger turbulence, various path-length and elevation angles. The dependence of scintillation on turbulence strength, path-length, and elevation angle is presented and the results are compared with the Rytov theory.

A novel high-power two-beam laser interference marking system is proposed. It is used to mark diffractive optical variable image on the surface of the glazed work piece directly. A high-power laser beam is split into two beams with equal energy. They are focused to form a spot composed of interference light field. The experimental results show that periodic micro-grating structure can be achieved with a single shot of laser ablation. Diffractive optical variable image, which is composed of micro-grating structures with different directions and different periods, has diffractive chromatic dispersion effects under the illumination of white light. The wavelength of the laser is 527nm. The energy of the single-pulse laser is 1.0mJ@20ns 20ns. The materials can be the stainless steel, the chromium film and other metals. The experimental results have been given.

A low cost adaptive optical system for improving solid-state laser beam quality has been set up. This system consists of a deformable mirror, a high voltage amplifier, a set of solid-state laser system, a CCD camera, a control software and corresponding optimization algorithm. This adaptive optical system doesn't employ a wave-front sensor to detect the phase information, but optimize the light intensity within a fixed aperture in the focal plane by a 19-element piezoelectricity deformable mirror. In order to find the optimum surface profile of the deformable mirror, which is applied to correct the phase aberrations in a solid-state laser system, a global genetic algorithm is introduced. The far-field light intensity signal, which is measured by a CCD camera, is used as a fitness function of the genetic algorithm. In this paper, the performance and efficiency of this wave-front sensor-less adaptive optical system based on the genetic algorithm are presented. Both the simulation results and the experimental results are given and discussed.

The thermal conductivities of nine different synthetic garnet laser crystals at various temperatures, range from 273 to 393 K have been investigated by instantaneous measurement method. The results show that the thermal conductivity of each crystal decreases exponentially with the temperature increasing. It is notable that, different host crystals, such as YAG, GGG, and GSGG have different thermal conductivity, which is attributed to the crucial influence of crystal structure and composition on the absolute value of their thermal conductivity. Moreover, with respect to the same host crystals, the impurity scattering also results in the change of their thermal conductivities. This is because that a higher concentration of doped ions leads to a more phonon scattering modes, which results in a shorter mean free path of the phonons and a lower thermal conductivity. In addition, different host crystals have various dependences of thermal conductivity on dopant concentration. This works provides reliable and useful information for designing high power, high quality, and high stability laser devices.