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- Front Matter: Volume 8904
- High Power Lasers and Applications
Front Matter: Volume 8904
Front Matter: Volume 8904
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This PDF file contains the front matter associated with SPIE Proceedings Volume 8904, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
High Power Lasers and Applications
Pulsed laser deposited cobalt-doped ZnO thin film
Show abstract
To realize the room-temperature ferromagnetism (RTFM) in diluted magnetic semiconductors (DMS), we
prepared a series of Cobalt-doped ZnO thin films using pulsed laser deposition (PLD) at deposition temperatures 500°C
under oxygen pressure from 2.5×10-4 Pa to 15 Pa. To elucidate the physical origin of RTFM, Co 2p spectra of
cobalt-doped ZnO thin films was measured by X-ray photoelectron spectroscopy (XPS). The magnetic properties of
films were measured by an alternating gradient magnetometer (AGM), and the electrical properties were detected by a
Hall Effect instrument using the Van der Pauw method. XPS analysis shows that the Co2+ exists and Co clusters and
elemental content change greatly in samples under various deposition oxygen pressures. Not only the valence state and
elemental content but also the electrical and magnetic properties were changed. In the case of oxygen pressure 10 Pa, an
improvement of saturation magnetic moment about one order of magnitude over other oxygen pressure experiments, and
the film exhibits ferromagnetism with a curie temperature above room temperature. It was found that the value of carrier
concentration in the Co-doped ZnO film under oxygen pressure 10Pa increases about one order of magnitude than the
values of other samples under different oxygen pressure. Combining XPS with AGM measurements, we found that the
ferromagnetic signals in cobalt-doped ZnO thin film deposited at 500 °C under oxygen pressure 10 Pa only appear with
the detectable Co2+ spectra from incompletely oxidized Co metal or Co cluster. So oxygen pressure 10 Pa can be
thought the best condition to obtain room-temperature dilute magnetic semiconductor about cobalt-doped ZnO thin
films.
Performance of smoothing by spectral dispersion combined with distribute phase plate on SG-II
Show abstract
Experimental performance of one-dimensional (1D) smoothing by spectral dispersion (SSD) combined with distributed
phase plate (DPP) on the ninth beam of SG-II is presented. Without the application of SSD, normalized focal-spot
non-uniformity of an 85% energy concentration is about 60%. Then, spectral bandwidth of the 3-ns, 1053-nm laser pulse
is broadened to 0.3 nm (as 270GHz in 3ω) by a 3-GHz modulator and a 10-GHz modulator integrated in the front-end
system. Spectral dispersion of 236 μrad/Å is achieved by a Littrow-configuration, 1480-l/mm grating placed between the
Φ40mm faraday isolator and the third Φ40mm rod-amplifier. By using such SSD, normalized non-uniformity with the
same energy concentration is decreased to 16%. A scheme of spatial power spectral density (PSD) in different directions
is adopted to analyze the intensity distribution of the far-field irradiation. Based on the spatial PSD analysis, theoretical
predictions of spectral peak caused by SSD’s color cycles is in excellent agreement with the experimental result. With
double-frequency modulation, the amplitude of the spectral peak is reduced by ~10dB. The temporal waveform of the 1ω
laser is measured. Waveform distortion criterion defining the frequency modulation to amplitude modulation conversion
(FM-to-AM) is about 6% with 1ω laser energy of ~1.8kJ.
Effect of nonideal wavefront on the near filed beam quality disturbed by flaw in target system
Show abstract
In high-power laser facilities for inertial confinement fusion, there are many large-diameter optical elements, which
inevitably have some flaws on the surface. The beam is modulated by these flaws after diffraction transmission, thereby
reducing the beam quality of the system. The optical field with high modulation may cause self-focusing in fused silica
and thus damage the optical components, which seriously affects the load capacity of the device. Therefore, for
high-power laser systems, near field beam quality also has a high demand. In this paper, the effect of flaws and nonideal
wavefront of sinusoidal modulation on the near-field quality at specific position behind the focusing lens is analyzed for
final target system of high power laser device based on the Huygens-Fresnel diffraction theory. Firstly the beam
modulation of ideal wavefront disturbed by flaws is investigated. And the modulation by phase type flaw is more serious
than amplitude type. Secondly, near field beam modulation of nonideal wavefront of sinusoidal phase disturbed by flaws
is analyzed. Results demonstrate that under some specific conditions of sinusoidal phase, modulation degree is reduced
and the beam quality is improved by the nonideal wavefront compared to the ideal wavefront. The results could give
some references to the improvement of near field beam quality and mitigation of risk of optical damage caused by
self-focusing.
Application of delrin in laser plasma micro-propulsion
Show abstract
The interaction between polymer of Delrin with nano-second pulse laser is investigated in laser plasma micro-propulsion.
The coupling coefficient and specific impulse are measured respectively. The coupling coefficient about 42 dyne/W and
specific impulse up to 646 s have been obtained. Moreover, the surface images after ablation have been observed. It is
found that Delrin has less debris on ablation surface. This indicates that Delrin is a potential polymer material in laser
plasma propulsion.
Study on the output of LD-pumped passively Q-switched subnanosecond microlasers
Show abstract
Caliber mortar projectiles and bombs are now tend to use the laser fuze because of its high accuracy in
distance measurement,the strong ability to resist electromagnetic interference, the high angular resolution and the good
concealment. Otherwise, the microlaser can bring about some alluring benefits. For instance, it can generate high quality
laser beam, which has small divergence angle and high power. So, This paper summarizes some key factors which have
impacts on the output of LD-pumped passively Q-switched subnanosecond microlasers, including the initial transmission
of the absorber, the reflection of output coupler, the length of the cavity and the radius of the pumping laser beam, and
gives the conclusion of the simulation based on the variation of the density of the reversal particle in the resonant cavity
derived from the oscillation equation of the LD-pumped passively Q-switched Cr4+:YAG/ Nd:YAG laser, which
provides the basis for the design of the passive Q-switched micro lasers which have high power, high repetition
frequency and narrow pulse width.
LD pumped high-repetition-rate high-power 532nm Nd:YAG/LBO solid state laser
Show abstract
Diode pumped solid state 532 nm green laser is widely required for many industrial, medical and scientific applications.
Among most of these applications, high power quasi-continuous-wave (QCW) green laser output is demanded. This can
be efficiently achieved through a diode-side-pumped acoustic-optic Q-switched Nd:YAG laser with an intracavity second
harmonic generation (SHG). In our experiment, LBO crystal is used for the second harmonic generation of
high-average-power lasers of near infrared (NIR) range, though its effective NLO coefficient deff is relatively small. It is
because of its high damage threshold (greater than 2.5 GW/cm2), large acceptance angle, small walk-off angle, and the
nonhygroscopic characteristic. In this paper, we reported a high-repetition-rate high-power diode-side-pumped AO
Q-switched Nd:YAG 532 nm laser. A plane-plane cavity with two rods, two AO Q-switches and the type II critical
phase-matched LBO at room temperature were employed. Under the LD pump power of 480 W, 95.86 W at 1064 nm
wavelength was achieved when the repetition rate was 15 kHz, and the 532 nm average output power of 44.77 W was
obtained, with a pulse width of 111.7 ns, corresponding to an optical to optical conversion efficiency of 46.7% from 1064
nm to 532 nm. The 532 nm average output power was 40.10 W at a repetition rate of 10 kHz with a pulse width of 78.65
ns. The output characteristics of the SHG varying with the pumping current and the pulse repetition frequency (PRF) of
the laser were also investigated. Further improvement of the SHG is under study.
Long-pulse laser design and experimental work
Show abstract
Long pulse laser starts to have a prominent role in many applications. So, How to design and calculate the parameters of
the high power long-pulse solid-state laser is illustrated, experimentally and arithmetically. How to design a pumping
chamber is illustrated, with a double-ellipse cavity. Optical resonator losses are got experimentally in details. Efficiency
factor and system slope efficiency are calculated experimentally. Illustration for how to get the optimum mirror
reflectivity is mentioned. Beam waist and beam divergence also studied experimentally. The designed system has 10J
output energy with pulse width 20msec for efficiency factor 1.1% and a combined loss 0.181 inside resonator. Average
system efficiency, gain coefficient and fluorescence power for four different output mirror reflectivity are 0.328%,
0.00994cm-1 and 144.92W respectively. 6KW/cm2 power density inside resonator is obtained which corresponds to
585W maximum output power. An optimum mirror reflectivity 57% is for 208.2KW input power. The beam waist and
beam divergence are recorded to be 0.66cm and 8.86mrad. Calculations show that, 11.7J output energy can be obtained
by more optimization based on the designed system.
Gain and reflective index combination guiding in a rod laser amplifier
Show abstract
The gain and refractive index combination guiding is investigated by simulating a dual-end pumped rod Nd:YVO4
amplifier. From the simulation, it is indicated that the large transverse gain gradient and the gain coefficient are
contribute to the gain guiding to enhance the beam quality. The appropriate spherical aberration in the input beam is
helpful for improving the beam quality of output beam. Moreover, the gain saturation determines which one could
dramatically influence beam quality between the gain guiding and the refractive index guiding.
Numerical research of two-dimension temperature distribution in bio-tissue induced by pulse laser and continuum laser based on FEM
Ning Shan,
Renjun Zhan,
Heping Cui
Show abstract
Laser has several advantages, such as strong anti-interference ability, quick speed, high power, agility and precision. It is
widely applied in military and medicine fields. When laser acts on human body, biological tissue of human body will
appear the phenomenon of ablation and carbonization and solidification. In order to effectively defend excess damage by
laser, the thermal effect research of skin tissue should be carried out. The heating rate and thermal damage area should
be studied. In the paper, thermal energy production and thermal exchange loss used in living tissue is analyzed. The rule
of thermal transfer that is irradiated by high power laser is discussed. The model of two dimensional skin tissues is built.
The two dimensional transient temperature distribution generated by laser irradiation in bio-tissue is numerical simulated
using finite element method. The temperature change trend generated by pulse laser and continuum laser in different
radial length and axial depth bio-tissue are studied respectively. The results show that FEM method can reflect the
photothermal conversion of bio-tissue exactly. Temperature is the highest in the local tissue by laser irradiated directly.
The highest temperature decreases along with increasing radial length and axial depth. The highest temperature rise
generated by pulse laser is more than continuum laser’s. The highest temperature generated by pulse laser is not
monotone increasing but is oscillation trend. The highest temperature generated by continuum laser is monotone
increasing. The temperature rise mainly occurs in exodermis and derma. The temperature rise is not very significant in
fat acid lining.
The research of atmospheric transmittance of high power laser along a ground-space slant path
Y. Wang,
Y. Liu,
H. Li,
et al.
Show abstract
The atmospheric transmittance of high power laser along a ground-space slant path has been comprehensively
investigated in this paper, which could be used for performance prediction and parameter estimation in the field of
laser engineering. First of all, the atmospheric transmittances along a ground-space slant path are studied with the
different launch parameters of high power laser. The center wavelength of laser is a critical element that affects the
atmospheric transmittance, while the influences of other parameters can be almost negligible. The atmospheric
transmittances of high power laser along a ground-space slant path are secondly researched under the different
meteorological conditions. The atmospheric transmittances of high power laser along a ground-space slant path are
lastly calculated under the different propagation conditions. The results indicate that atmospheric transmittance
through the whole atmosphere decreases as the zenith angle increase; the differences remain in 2 percent when the
zenith angle is less than 20 degree for 532nm laser. In the view of propagation length, it is the range below the
altitude of 6km that mainly affects the transmittance of high power laser along a ground-space slant path.
Linewidth influenced by phase modulation and frequency modulation in optical feedback diode laser
Show abstract
We derive and calculate numerically laser linewidth by means of the laser rate equation in an extending diode laser
cavity provided by an end reflector. We found that narrow linewidth is closely connected with phase modulation and
frequency modulation. The numerical simulation shows the dominance of effect over another depends on inherent factors
such as the α coefficient, bandwidth of laser, length of external cavity, reflective coefficient etc.
Power scaling and beam divergence compression of bottom-emitting vertical-cavity surface-emitting lasers
Show abstract
Power scaling and beam divergence compression of 980 nm bottom-emitting vertical-cavity surface-emitting lasers
(VCSELs) are presented in this paper. First, the relationships among the reflectivity of the n-doped distributed Bragg
reflector, threshold current, and output power were analyzed, and the n-DBR reflectivity was optimized to achieve higher
slope efficiency in a relatively low threshold current. Second, the influence of the p-contact on the current density
distribution inside the active region was analyzed using the three-dimensional finite-element method. Uniform current
distribution was achieved by optimizing the diameter of the p-contact, and a consequent improvement in beam
divergence was observed. A low divergence of 5.4° was obtained for a single device with continuous-wave (CW) of 1.46
W at room temperature. The 8×8 VCSEL array showed a divergence angle of 10.2° at 4A. This array afforded a CW
output power of 1.95 W under an injected current of 4 A and a pulse output power of 115 W under a pulse drive current
of 130 A, a pulse width of 100 ns, and a repetition frequency of 100 Hz. VCSEL array chips were packaged in series to
form a “quasi-array” to further increase the output power. This series achieved a peak output power of 475 W under a
pulse drive current of 120 A.
Theoretical research on damage mechanism of ultrafast laser ablation crystal silicon
Show abstract
High peak power picosecond laser ablation of silicon draws great attention in solar cell manufacture,laser optoelectric countermeasure applications, eta. This paper reports the damage process of ultrafast lasers interaction with silicon,which is based on Two-Temperature Model(TTM) and 1-on-1 damage threshold test method. Pulsed laser caused damage manifests in several ways, such as heat damage, mechanical effect and even eletrical effect. In this paper, a modified Two Temperature Model is applied in ultrashort laser interaction with silicon.The traditional Two-Temperature Model methods is proposed by Anismov in 1970s to calculate the interaction between ultrafast laser with metals, which is composed of free electrons and lattice. Beyond the carrier and lattice temperture model, an additional excited term and Auger recombination term of carriers is taken into account in this modified Two-Temperature Model model to reflect the characteristics in semicondutors. Under the same pulse-duration condition, the damage threshold is found to be 161 mJ/cm2 and a characteritic double-peak shape shows up. As the pulse energy density rises from 50mJ/cm2 to 161 mJ/cm2, the difference between carrier and lattice temperature steps down proportionally.Also,a detailed interaction process between photon-electron and electron-phonon is discussed. Electron and lattice temperature evolutes distinctly different, while the former is much higher than the latter until heat tranfer finished at 200 picoseconds. Two-peak feature of electron temperature is also identified. As the pulse duration increases from 20 picosecond to 60 picosecond, the he difference between carrier and lattice temperature steps down significantly. The calculated damage threshold does not change fundamentally, remaining approximately 0.16J/cm2. Also, the damage mechanism is found to be thermal heating with the pulse width between 20 and 60 picoseconds at threshold fluences which is identical to experiment test result. This research is valuable to laser applications and/or laser shielding applications.
Design criteria of end-pumped Nd:YAG zigzag slab amplifiers
Show abstract
Criteria of selecting the slab size in high-power end-pumped Nd:YAG zigzag amplifier were
given, the optimized slab thickness is suggested 2~3 mm, with the corresponding slab length less than 15 cm.
Power extraction in the slab was calculated by a smart ray tracing technique, the optimized input flux is 3~4 times
the saturated flux (Is) with a maximum optical-optical (o-o) efficiency of 44.5% for the single-slab single-pass
stage, and 0.1~0.2 Is with a maximum o-o efficiency of 41% for the four-slab angularly double-pass stage.
A four kHz repetition rate compact TEA CO2 laser
Show abstract
A compact transversely excited atmospheric (TEA) CO2 laser with high repetition-rate was reported. The size of the laser is 380 mm×300 mm×200 mm, and the discharge volume is 12×103 mm3. The laser cavity has a length of 320mm and consists of a totally reflective concave mirror with a radius of curvature of 4 m (Cu metal substrate coated with Au) and a partially reflecting mirror. The ultraviolet preionization makes the discharge even and stable,the output energy can be as high as 28 mJ under the circumstance of free oscillation, and the width of the light pulse is 60ns.To acquire the high wind velocity, a turbocharger is used in the system of the fast-gas flow cycle. When the wind speed is 100m/s, the repetition rate of the transversely excited atmospheric CO2 laser is up to 2 kHz. On this basis, a dual modular structure with two sets of the gas discharge unit is adopted to obtain a higher pulse repetition frequency output. The dual discharge unit composed two sets of electrodes and two sets of turbo fan. Alternate trigger technology is used to make the two sets of discharge module work in turn with repetition frequency of 2 kHz, the discharge interval of two sets of the gas discharge unit can be adjusted continuously from 20 microseconds to 250 microseconds. Under the conditions of maintaining the other parameters constant, the repetition frequency of the laser pulse is up to 4 kHz. The total size of laser with dual modular structure is 380mm×520mm×200mm, and the discharge volume is 24×103 mm3 with the cavity length of 520mm.
High energy quadruple pass amplifier for high power laser preamplifier module
Show abstract
Pre-amplifier between the frontend and main power amplifier is the key unit of high power laser divers. The recent
progresses on the off-axis quadruple pass amplifier are presented, which include the beam path design, parasitic
oscillation research and experimental results. A single longitudinal mode, temporally shaped laser pulse with 5ns pulse
duration at 1053nm is injected into a Nd: Glass regenerative amplifier, which can provide a 12mJ energy output with
0.5% long term energy stability. The quadruple pass amplifier is designed as an off-axis pattern. With 1.3mJ energy
injection, amplified pulse with 16.5J can be achieved, and the measured output energy stability of the amplifier is 7.3%
(PV) at this output energy level, corresponding to a 21 shot result. The total gain of the amplifier is more than 10,000.
The parasitic oscillation was analyzed and discussed, and the parasitic mode and pencil beam are neither observed in the
experiment.
The influence of energy deposition parameters on laser plasma drag reduction
Show abstract
Laser plasma drag reduction is a new method to reduce the wave drag of hypersonic flight. The research of the laser
plasma drag reduction performance is an important work. The purpose of this paper is investigating laser plasma drag
reduction by numerical simulation to enhance the understanding of the drag reduction mechanism, get the drag reduction
performance in different conditions, and provide references for laser plasma drag reduction experiment in the future.
Based on summarizing correlative references systematically, through building the model of energy deposition and
comparison the simulated results to the empirical formula and computation results to verify the program correctness, the
influence of laser energy parameters to laser plasma drag reduction were simulated numerically for optimize the
performance. The follow conclusions were got by numerical simulation:
The computation program can well simulate the interacting of LSDW(laser supported detonation wave) to the bow
shock in front of the blunt body. Results indicate that the blunt body drag could be decreased by injecting laser energy
into the incoming hypersonic flow. The correctness of program was verified by compare result to the experiment and
computation results.
Blunt body drag will be greatly decreased with injected laser power increased, The bigger laser power is injected, the
more drag decreases. There’s an energy saturation value for each laser power level, the injecting laser power
effectiveness values are never quite high for all laser power level.
There is an optimized energy deposition location in upstream flow, this location is right ahead of the blunt body.
When the distance from deposition location to the surface of blunt body is 5 times the blunt radius, blunt body drag
decreased the most.
This paper investigated the parameters which primary influence the performance of drag reduction. The numerical
simulation data and obtained results are meaningful for laser plasma drag reduction experiment investigation.
Aerodynamic drag, laser plasma, hypersonic, drag reduction, numerical simulation
Second harmonic generation study of the air/liquid interface of different solutions
Show abstract
As an intrinsically surface-specific technique, Second Harmonic Generation (SHG) is widely used in the study of
interface in recent years. The SHG signals from the air/liquid interface of Rhodamine B and Sodium Dodecyl Benzene
Sulfonate (SDBS) aqueous solutions were obtained and analyzed, which demonstrate that the SHG signal intensity of
Rhodamine B is stronger than that of SDBS. Compared with one single solution, the SHG signal intensity of the mixed
aqueous solution of Rhodamine B and SDBS decreases. From the UV-VIS absorption spectrum of the two aqueous
solutions, it can be seen that Rhodamine B has an absorption peak closer to the second harmonic frequency. Therefore
the resonance of the second harmonic frequency with the frequency of the dipole transitions of the chromophore
considerably enhances the signal intensity. Furthermore, the hyperpolarizabilities of the molecules of Rhodamine B and
SDBS are calculated from first-principles, which reveal that the hyperpolarizability of Rhodamine B molecule is greater
than that of SDBS molecule. When they are mixed, molecules of Rhodamine B and SDBS gather together because
Rhadamine B molecule carries positive surface charge and SDBS is anionic surfactant, causing the decrease of the SHG
intensity of the mixed solution.
Morphology and chemical composition analysis on multi-pulsed CO2 laser ablation of HgCdTe crystals
Show abstract
In order to study deeply damage mechanism of HgCdTe crystal irradiated by multi-pulsed CO2 laser and obtain the
characteristics of surface morphological and chemical composition changes. Firstly, Irradiation effect experiment is
conducted on the Hg0.826Cd0.174Te crystal by pulsed CO2 laser, which has a pulse width of 200ns and repetition frequency
ranges from 1 Hz to 100 kHz. Then morphological and chemical composition changes of Hg0.826Cd0.174Te crystal is
measured by field emission scanning electron microscope (FESEM) and damage threshold is obtained by morphology
method. Finally, the impact of laser power density on morphological and chemical composition changes is analyzed. The
research results show that: damage threshold of Hg0.826Cd0.174Te crystal which is irradiated by multi-pulsed CO2 laser is
950 W/cm2. The crystal surface melting phenomenon is very obvious, the obvious crack which is caused by thermal
stress is not found in the surface, and a large number of bulges and pits are taken shape in the laser ablation zone.
Chemical composition changes of the crystal are obvious, and a lot of O element is found in the laser ablation zone. With
the increase of laser irradiation power, the content of Hg element decrease rapidly, the content of Cd, Te and O element
raise by degrees, and chemical composition changes of the crystal are more and more obvious. When the irradiation
power density is 1.8kW/cm2, the surface becomes smooth in the ablation zone due to the impact of laser impulse force,
and the content of the chemical compositions is that Hg accounts for 0.23%, Cd accounts for 21.38%, Te accounts for
26.27%, and O accounts for 52.12%. The conclusions of the study have a reference value for the Hg0.826Cd0.174Tecrystal
in the application of making infrared detector and pulsed CO2 laser in the aspect of laser processing.
Numerical study of thermal stress damage in dielectric film by long-pulse laser
Show abstract
In this paper, we study and establish the theoretical model of thermal stress damage of dielectric film in film/substrate
systems caused by long-pulse laser, based on which transient distributions of temperature field and thermal stress field
are simulated using the finite element method(FEM) and then analyze the mechanism of the damage. In accordance with
the basic equation of heat conduction equation and thermal stress equation, the physical model of dielectric film and the
substrate transient temperature field and thermal stress field is developed with the assumption that the dielectric film and
the substrate are isotropic and their thermal parameters do not change with temperature.
On the foundation of theoretical analysis, transient of temperature field in dielectric film in film/substrate systems under
long-pulse laser irradiation is simulated and calculated. The numerical results indicate that great temperature gradient
exists in dielectric film and substrate in radial direction but smaller one exists in axial direction. When the laser power
density is increasingly larger, the temperature gradient in radial direction is larger and the temperature in the center of the
film is higher. Transient thermal stress field in dielectric film in film/substrate systems under long-pulse laser irradiation
is simulated. Numerical results show that, the damage to the dielectric film caused by long-pulse laser is mainly due to
thermal stress damage process which circumferential stress acts a primary role in. Such damage is a final result of the
substrate being under thermal stress. For film/substrate system, the damage under long-pulse laser radiation starts from
the substrate. When the laser power density is increasingly larger, the dielectric film is more vulnerable to damage and
damage zone is greater.
The result of this paper provides theoretical foundation not only for research of theories of dielectric film and substrate
thermal stress damage and its numerical simulation under laser radiation but also for long-pulse laser technology and
widening its application scope.
The influence of the inflow speed on air-breathing supersonic laser propulsion
Show abstract
A model of coupled dynamics for supersonic airbreathing propulsion is developed to simulate the development process of the thruster’s flowfield. The influence of the inflow speed, from 1 to 4 Mach, on the laser propulsion performance is investigated numerically. The results indicate that the inflow speed has a marked effect on the propulsion efficiency. Under the same laser parameters, the larger inflow speed leads to lower thruster and impulse coupling coefficient. By analyzing the phenomena in the complex unsteady flowfield, we found that the bow shock occurring out of the surface of the thruster due to supersonic inflow is the real cause of the performance worsening and air drag reduction becomes a very important task at supersonic laser propulsion.
Flat-top temporal and spatial profiles femtosecond pulse beam generated by phase only modulating
Show abstract
The method for generating temporal flat-top waveform and spatial flat-top profile
femtosecond pulse beam by phase and polarization controlling is proposed and demonstrated. Based on
direct wave front phase modulating, flat-top spatial intensity distribution can be obtained. Combining a
folded 4f zero-dispersion system with a polarization controlling setup, the temporal flat-top waveform
is generated. Experimental results indicate that for the input both temporal and spatial Gaussian pulse
beam with 363 fs temporal width and 1.5 mm beam waist, the temporal width of the output shaped
pulse beam is 1.2 ps and 1.9mm beam waist, and the rms variation is about 9.2%, which prove that the
temporal flat-top and spatial flat-top femtosecond pulse beam can be generated effectively.
Phase compensating algorithm investigation of real-time adaptive femtosecond pulse shaping
Show abstract
Based on the real-time adaptive femtosecond pulse shaping system, the phase compensating algorithms
which can effectively compensate the output shaping waveform distortions are investigated in detail.
The simulated-annealing algorithm that can modify the output pulse temporal waveforms iteratively
toward the target shapes using the second harmonic generating frequency resolved optical gating
(SHG-FROG) measurement as feedback is proposed. Compared with the cross-correlation feedback
measurement method, the output based on the SHG-FROG measurement method is better and the
temporal chirp of the output pulse is compensated more effectively. Moreover the performance of the
SHG-FROG measurement feedback algorithm is compared to other exemplary standard approaches
such as the Genetic Algorithm based on the cross-correlation feedback measurement method, the result
is much better.
Output spectrum of high-power CW fiber amplifier
Show abstract
A generation spectrum of a high-power Yb-doped fiber amplifier (YDFA) becomes broader with increasing
power in the master oscillator power amplifier (MOPA) configuration, which degenerating the coherence of the
laser. In this work, a spectral model had been proposed for the high-power YDFA in Continuous Wave (CW)
region. A fiber amplifier was built at the 600W level and experiments were conducted for its output spectral
characteristics based on this model. Through this model, the output spectrum of high-power YDFA in CW
region could be calculated. Though the theoretical spectra were in little different from the measured ones, the
predictions of the theory were still in excellent quantitative agreement with the experimental results.
Analysis of the power scaling of resonantly pumped Tm-doped silica fiber lasers
Show abstract
The physical limit for the maximum extractable power of Tm-doped silica fiber lasers in resonantly-pumped
configuration is analyzed. The effect of thermal fracture, thermal lens, melting of the core, optical damage, finite pump
brightness and the nonlinear effects (stimulated Brillouin scattering or stimulated Raman scattering) are taken into
consideration. According to the numerical simulation, a maximum extractable power of 56.6 kW and 2.11 kW could be
achieved by theTm-doped fiber sources in resonantly-pumped configuration for the broad bandwidth and
single-frequency case, respectively. Strictly single-mode of these cases are also taken into consideration, and the
maximum extractable powers are 12 kW and 1.25 kW. The physical limit mechanism derived by this method proves that
the Tm-doped fiber sources in resonantly-pumped regime has a significant advantage over that in diode directly-pumped
regime, thus having practical significance for increasing the output power.
High-power all-fiber picosecond MOPA laser based on hybrid-doped Yb fibers
Show abstract
In this paper, we propose an optimized design of the picosecond MOPA fiber laser by using hybrid-doped Yb fibers. The
detailed implementation is that high-doped gain fiber with relatively small fiber core is adopted in the low-power
pre-amplifiers, thus the shortest fiber could be ensured and the thermal load is not so heavy. In the power amplifier stage,
the normal-doped large mode area gain fiber is utilized, then the thermal effects can be minimized and the output beam
quality could be ensured. The design simultaneously takes into consider the output beam quality, thermal load, nonlinear
phase shift, pulse peak power of the picosecond fiber laser. With using the existed Yb-doped fibers, we demonstrate a
high-power picosecond MOPA fiber laser with the proposed method. The average output power is up to 110 W, the total
optical conversion efficiency is 63.2%. No stimulated Raman scattering, amplified spontaneous emission and residual
pump light are observed in the output spectrum. The - 6 dB bandwidth of the output spectrum at the full output power is
~ 4 nm.
The mechanism of laser disturbing infrared detector and its intelligent protection
Show abstract
Interference mechanism of laser disturbing infrared detector is analyzed. The disturbing grade was
separated into four levels according to interference effect. The levels are saturation, melting,
vaporization and plasma. The responsivity of a detector will drop and it can’t work effectively when it was saturated. Its performance wills recovery when the interference disappeared. Melting, Vaporization
and plasma will lead to permanent damage. The main damage to detector is thermal damage for
induced laser. The reason is that the detector will melt or evaporate when it absorbed the energy of induced laser. For HgCdTe detector, the damage appeared as Hg precipitation. It appeared as In exfoliated from welding outlet line of HgCdTe crystal or HgCdTe melting when the temperature of detector is higher. Since Vanadium Oxide has reversible transformation characteristic between
semi-conductor, metal and insulator, it can be used to protect detector from laser damage. Vanadium Oxide can be made as thin film coatings on optical system to protect the detector. the phase transformation point temperature of VO2 is 68°C,a few doping method can decrease the transformation
temperature. These mean that less energy can make VO2 film’s temperature increase to transformation
point. VO2 film protecting HgCdTe detector was used as an example to estimate the protection effect.
For an HgCdTe detector, its responsivity will drop two orders of magnitude when its temperature raises 70K. This case be regard as that the detector was disturbed. When a CO2 pulsed laser beam with 0.1μ
s∼10μs pulse width was incidence an HgCdTe detector, its heat conduction depth is 0.32∼3.2μm and its thermal diffusion can be ignored. The damage energy density threshold value is Ein=1.55J/cm2.
When CO2 pulsed laser beam incidence the detector through certain thickness VO2 film, the VO2 film
will has transformed from semiconductor state to metallic state before the laser beam damage the
detector. The energy of the laser beam will be total reflected. VO2 can be used as an intelligent preventer to protect detector against laser.
Numerical simulations of high power near-infrared supercontinuum generation from a nonlinear fiber amplifier
Show abstract
Photonic crystal fiber has been widely used in visible and near-infrared
supercontinuum generation due to its flexible dispersion control and high nonlinearity.
However, the maximum average output power of supercontinuum from a photonic crystal
fiber has not exceed one hundred watt owing to the small core diameter of the photonic
crystal fiber and the low coupling efficiency between the pump and the photonic crystal fiber.
Recently, supercontinuum generation directly from a nonlinear fiber amplifier attracts lots of
attention as a result of its simple structure and low splicing loss and many excellent results
have been achieved either in low and high average power, which is proved to be a promising
method to realize kilowatt level high power near-infrared supercontinuum. However, the
numerical study on high power near-infrared supercontinuum generation from a nonlinear
fiber amplifier has been rarely reported, so there is great necessity to carry out some
theoretical study on it. In this paper the complex Ginzburg-Landau equation is used to
describe the formation and propagation of high power near-infrared supercontinuum
generation in a nonlinear fiber amplifier. The chromatic dispersion of the ytterbium-doped
fiber is measured by a Mach-Zehnder interferometer. The roles of the small signal gain, input
pulse width and initial chirp of the input pulse played on the continuum formation are
analyzed in detail. The results are in good agreement with the experiments which can provide
some theoretical guidance on future optimization of the flatness and width of the
supercontinuum generation from a nonlinear fiber amplifier.
Influence of storage causing packaging stress changes on smile effect for diode laser arrays
Show abstract
The smile effect is caused by the thermal stress in the packaging process. If packaging technology of a diode laser array
is poor, smile effect will be very bad and the smile effect will vary with storage time. To accurately measure smile effect
and to objectively compare the different measuring methods for smile effect, a set of optical system is designed for
measuring the smile effect. By using an image amplification method, the smile effect of a diode laser array is accurately
measured, and the measurement error is about ±0.1μm. By researching, the heat sink surface flatness has little influence
on smile effect. However the solder quality is a critical factor for smile effect. That is to say, there is more voids, the
corresponding smile effect is more serious in this area. Reflow soldering curve has a major impact on smile effect in the
packaging process of a diode laser array .During reflow soldering process, accelerated cooling before solidification and
slow cooling after solidification not only can commendably reduce voids and smile effect ,but also can effectively solve
the smile effect with storage time variation problem .By optimizing the reflow soldering curve of a diode laser array , the
smile effect has been controlled within ±0.5μm..As the smile effect values of a semiconductor laser array is diminished
and the beam quality of a laser diode array is improved significantly. The recommended method provides favorable
conditions for the beam collimation and shaping of a semiconductor laser array.
The technique of high power laser beam combination using liquid crystal spatial light modulator
Show abstract
Based on the phase modulation characteristics of optically addressed liquid crystal spatial light modulator
(OA-LC-SLM) which is realized by controlling the power of addressing light, a physical model of coherent beam
combination fiber laser using a bunch of fibers and a device of OA-LC-SLM is established on the theory of
diffraction optics and liquid crystal birefringence effect. On the basis of this model, the properties of given scheme
of coherent beam combination fiber laser are investigated including main lobe distribution and ability of phase
modulation. Meanwhile, the plot functions of phase modulation versus the optical power of addressing light are
obtained on different given driving voltage conditions and fiber alignment parameters such as core diameter and
filling factor. After the numerical simulation, it shows that, this coherent beam combination fiber laser using
OA-LC-SLM demonstrates an ability of coherent beam combination on the far field. With the increase of core
diameter, the combination efficiency is improved better, and the divergence angle decreases narrower.
Design and development of 24 times high-power laser beam expander
Show abstract
As currently, laser calibration, laser radar, laser ranging and the relative field raised up the demand for high
magnification laser beam expander. This article intends to introduce a high-energy laser beam expander research and
design, large- diameter, wide-band, high-magnification and small obscuration ratio are the main features. By using
Cassegrain reflective optical system, this laser beam expander achieves 24 times beam expand, and outgoing effective
limiting aperture is Φ600 mm, band scope between 0.45μm to 5μm, single-pulse laser damage threshold greater than
1J/cm2, continuous-wave laser damage threshold greater than 200W/cm2 and obscuration ratio 1:10. Primary mirror
underside support uses 9 points float supporting, lateral support mainly depends on mercury belt support and assists by
mandrel ball head positioning support. An analyzing base on finite element analysis software ANSYS, and primary
mirror deformation status analysis with debug mode and operativemode, when inputs four groups of Angle 170°, 180°,
210° and 240° , mercury belt under each group of angle load-bearing is 65%, 75% , 85% and 100% respectively, totally
16 workingcondition analyze results. At last, the best way to support primary mirror is finalized. Through design of
secondary mirror to achieve a five-dimensional precision fine-tune. By assembling and debugging laser beam expander,
Zygo interferometer detection system proof image quality (RMS) is 0.043λ (λ=632.8nm), stability (RMS) is 0.007λ
(λ=632.8nm), and effective transmission hit 94%, meets the requirements of practical application completely.
Experimental research on mechanism of phase noise of laser amplifier
Show abstract
Coherent combination of multiple laser amplifier is an important technique for high power and high beam quality laser.
Laser amplifier uses master oscillator power amplifier (MOPA) configuration for narrow bandwidth and high beam
quality laser. Then active phase control is used to make multiple laser amplifier phase synchronization for coherent spot
in the far field. The center spot is N times brighter than the one of incoherent combination. At present, researchers have
used this method to achieve 1.56kW coherent combination of nine fiber lasers and 105kW of seven slab lasers.
The phase noise of the laser amplifier is an important factor affecting the coherent combination. There are two key
technologies in the coherent combination. The one is fill factor of multiple laser spatial distribution, which determines
main lobe energy of coherent spot. And the other is the phase noise of the laser amplifier, which decides stability of the
coherent combination. The phase noise of laser amplifier is caused by many factors, mainly thermal disturbance and
mechanical vibration. Due to the complexity of the phase noise generation, the research on phase noise is generally
concentrated in the qualitative analysis. The phase noise is generally considered the time phase noise. It is phase
dithering from variation refractive index by external disturbance. A variety of factors, such as temperature changes,
mechanical vibrations, the pump power, affect phase noise. We establish an externally imposed discrete disturbance
source on fiber laser amplifier and then analyze above-mentioned factors independently and quantitatively by the
method. The experiments demonstrate space phase noise, dithering of beam direction, is simultaneously induced by
either mechanical vibration or thermal disturbance. This experiment is significant for understanding mechanism of the
phase noise and suppression of phase noise.
Mid-infrared supercontinuum generated from a single-cladding Tm-Ho co-doped fiber
Show abstract
We report on the mid-infrared supercontinuum laser output using a short piece of single-cladding Tm-Ho co-doped fiber,
pumped by a 1565 nm pulsed laser. The seed laser was amplified using a two-stage Er-doped master oscillation power
amplifier (MOPA). The seed laser was amplified to 260.8 mW with repetition rate of 100 kHz. The amplified 1565 nm
pulse laser passed through a piece of 500 m long single-mode 9/125 G652D communication fiber, then the laser was
injected into a 2 m long 9/125 Tm-Ho co-doped fiber. The laser had output power of ~ 20 mW, and the laser’s spectrum
was measured by an optical spectrum analyser (YOKOGAWA). By changing the 1565 nm seed laser’s repetition rate and
pulse duration, mid-infrared supercontinuum was generated. The energy levels of Tm3+ and Ho3+ icons acted with the
different wavelength of the pulse laser, then flat and broadband mid-infrared supercontinuum between 1800 nm ~ 2200 nm
was generated. The output power can be scaled up by increasing the 1565 nm laser’s power directly. This supercontinuum
generated by single-cladding Tm-Ho co-doped fiber may provide meaningful reference for mid-infrared supercontinuum
generation using other rare-dearth-doped fibers.
Simulation for thermal blooming of the axial pipe flow
Show abstract
For the thermal blooming of the beam path indoor, solving the coupling equations of optical field and fluid field
completely is a meaningful and important subject. In this paper a numerical emulation platform for solving the coupling
equations was established. The laser beam coupled with the fluid field by the method of User Defined Function which
was offered by the CFD software. Thermal blooming effects in the beam path indoor of the line pipe are modeled by the
established numerical emulation platform. In order to testify the rightness of the numerical emulation results, steady-state
thermal blooming effects in the axial pipe flow are calculated by the theoretical methods, and corresponding experiments
are also carried out. The results indicate that the numerical emulation platform is creditable in simulating the thermal
blooming of axial pipe flow.
Optical nonlinearity measurements of copper phthalocyanine film
Show abstract
The nonlinear refractive response of a copper phthalocyanine film fabricated by the electro-deposition is
investigated by a modified top-hat Z-scan with 19 picoseconds pulse at wavelength of 532 nm. Compared to the top-hat
Z-scan, the curve of modified top-hat Z-scan for the nonlinear refraction shows a single peak rather than a peek-valley
curve. Furthermore, the sensitivity of this new technique can be more than two orders of magnitude enhanced. The
results show that the film has obvious response of nonlinear refraction. The theoretical simulation fit well with
experimental results.
Thermal effect in pulsed laser diode dual-end pumped Tm:YAG laser
Show abstract
Based on the actual working environment of pulse LD dual-end pumped Tm:YAG crystal, time-dependent temperature field analytical expression and the time-varying thermal focal length are deduced by the integral transform method. Additionally, the effects of pump power, repetition frequency and duty ratio on axial transient temperature distribution and time-varying thermal focal length of pulse LD dual-end pumped Tm:YAG rod are simulated and analyzed. The results show that the temperature distribution reaches steady state respectively by 11, 14, 15 pulses under pump power of 30W, 35W and 40W, respectively, while the frequency is 100Hz and the duty ratio is 50%. Under the condition mentioned above, the temperature of the crystal rod on both ends of the center arrives 34.7°C, 37.5°C, 40.3°C, which is 1.8°C, 2.1°C, 2.4°C higher than the center of rod. And the thermal focal length is in the range of 31.5-41.5cm, 26.5-34.6cm, 22.9-29.7cm, respectively. When pump energy is 100mJ, frequency at 110Hz, 120 Hz, 130Hz and duty ratio at 55%, 60%, 65%, respectively, the temperature distribution reaches steady state respectively by 13, 15, 16 pulses, and the temperature of the rod on both ends of the center respectively arrives 30.0°C, 30.9°C, 31.8°C, which is 1.3°C, 1.4°C, 1.5°C higher than the center of rod, and thermal focal length is in the range 46.4-58.8cm, 42.7-51.6cm, 39.5-45.9cm, respectively. Namely, as the increase of the pulses number, the distribution of the temperature and the thermal focal length in crystal rod appear jagged and eventually get to the periodic distributions. With the increase of the pump power, repetition frequency and duty ratio, the temperature difference between the crystal rod on both ends of the center and the center of rod is increasing, while time-varying thermal focal length gradually becomes shorter and the fluctuation range is smaller until it reaches steady state. The results provide theoretical basis for heating compensation and cavity design of pulsed thulium doped lasers.
Influence of BBO temperature distribution on phase mismatching distribution in fourth harmonic
Show abstract
266nm UV laser has a wide range of applications in various fields by its advantages in high single photon energy and
high resolution, which also has a development gradually moving in the direction of high power and high conversion
efficiency. In the process of high-power laser frequency doubling, BBO crystal inevitably absorbs part of fundamental
light power and frequency doubled light power, it induced the temperature rise along the direction of radiation in crystal
and destroyed the phase-matching conditions of BBO crystal that lead to phase mismatching. In order to improve
harmonic conversion efficiency as well as reduce the influence of output power and beam quality caused by phase
mismatching, in this paper we analyzed the process of phase mismatching, established the thermal-induced phase
mismatching model by using analytical expression of the nonlinear crystal temperature field equation which has been
given, and the three-dimensional phase mismatching distribution were obtained. There are three major contributions in
the paper. Firstly, the working process of the nonlinear crystal was analyzed, and the physical and mathematical models
of temperature distributions were established, and the BBO crystal three-dimensional temperature distributions were also
obtained. Secondly, a variety of factors that affect the temperature distributions within the BBO crystal were summarized.
For different 532nm waist radius and 532nm input power, they were numerical simulated use of MATLAB. Finally,
combined with the above analysis, the physical and mathematical models of phase mismatching caused by energy
absorption of BBO in forth harmonics generation were established, the phase mismatching distributions in the crystal
were simulated as well, especially the changes to phase mismatching distributions with different parameter were
analyzed. Combination of the multiplier theory, the influence of phase mismatching on frequency doubling conversion
efficiency was analyzed. The results indicate that the physical model which established in this paper can explain the
physical reasons in high-power laser frequency doubling system very well, such as the reduce in conversion efficiency
and output power and beam quality. All research results play instructive effect at the improvement of conversion
efficiency and the compensation for the phase mismatching for further research.
The research of wavefront compensation of a reflective beam shaping system
Show abstract
In order to compensate the low order aberrations effectively and rapidly, a new method is developed to study the
wavefront compensation of a reflective beam shaping system by using simulation experiments. The system consists of
three cylinder mirrors and a spherical mirror. By inserting different Zernike phase screens, many sizes and species of low
order aberrations can be simulated. Then the data communication is set up between Matlab and Zemax based on dynamic
data exchange (DDE) technique. The configuration parameters of the system constructed by Zemax could be regarded as
variables, and the beam shaping system as the transfer function, overall appropriate optimization algorithm was utilized
to solve the optimal configuration to make the compensation system most effective.
The comparison between MFD and MOI on the simulation of combiner insertion loss
Show abstract
Great progress has been made in fiber laser technology especially the high power fiber laser. One of the key
techniques to acquire higher output power is coupling more pump laser into the double-cladding fiber using the fiber
combiner. Fiber splices exist in both manufacture of the combiner and integration of the fiber components. The optical
waveguide structure of the splice point has great effect on the insertion loss and modal content for the fiber laser system.
Thus it is important to use proper method to compute the insertion loss of the splice points. This is also vital in the
manufacture of fiber combiner because the structure must be precisely controlled in order to acquire low insertion loss
for the signal arm of the combiner to ensure the capability of sustaining high power laser.
Generally speaking, there are two common methods to compute the insertion loss of splice points: the mode field
diameter (MFD) and the modal overlap integral (MOI). The MFD method is simple but its accuracy is relatively lower,
while the MOI is more accurate than the MFD but also more complicated. We use both two methods to compute the
insertion loss of the signal arm of a (6+1) ×1 fiber combiner. The result shows that the MFD method is appropriate when
there is only fundamental mode at the splice point. At the mode field matched point, the insertion loss is 0dB when using
the MFD method while 0.29dB when using the MOI method. This indicates that the MOI method is more accurate than
the MFD method to predict the minimum insertion loss and the optimal structure. Meanwhile, the MOI method can
explain the different insertion loss for the co-propagating situation and the counter-propagating situation for the fiber
combiner which cannot be explained by the MFD method. If there are higher order modes passing through the splice
point, the MFD method is also inappropriate.
LD dual-end-pumped CW Tm:YLF laser
Show abstract
We report on a LD dual-end-pumped 792nm continuous wave operation Tm:YLF laser. Firstly, the rate equation of LD end-pumped CW operation Tm:YLF laser were established, in which the energy transfer upconversion and without energy transfer upconversion under continuous-wave considerate were considered, as well the pump threshold and the slope efficiency of the laser system were analyzed. Simultaneously, the cavity stability condition and the pattern matching of the plano- concave resonator were analyzed according to ABCD Matrix theory. Comparing respectively the laser threshold and the slope efficiency and optical-optical conversion efficiency under circumstances which the output mirror transmittance of 15% and 23%. In addition, the M2 of the output laser were contrasted and analyzed in adjusting the resonator cavity length by using different radius of curvature of the output mirror in 150mm, 200mm and 300mm all in the above case. As the process of thermal lens focal length changing greater than 90mm, it exhibited that the two fundamental modes in the cavity resonator matched well in numerical simulation when the radius of curvature of the output mirror was 300mm, as well the two fundamental modes matched well when it more than 100mm in a certain pump power. We designed a single LD dual-end-pumped continuous wave operation Tm:YLF laser. Using Tm:YLF (3 at.%) crystal for gain medium, which the size was 3×3×14mm3. In experiments, the Tm:YLF laser crystal keeps 291K and the temperature control method is water cooling. The length of the resonator was 135mm when L shape plano-concave resonator was applied, and the radius of curvature output mirror was 300mm, as well as the temperature of the Tm:YLF laser crystal was 291K. The output laser we observed by this system and the central laser wavelength was 1944nm. The threshold power was 8.11W and the highest output power reaches to 4.01W when the totally input pump power was 17W, and the optical conversion efficiency was 23.6%. The far-field divergence angle was 3.8mrad after calculation. Respectively. The experimental results are coinciding with the theory.
Numerical analysis of supercontinuum generation in cascaded photonic crystal fiber tapers
Show abstract
The concept of cascading Photonic Crystal Fiber (PCF) tapers is proposed, and the numerical model of supercontinuum
(SC) generation in cascaded PCF tapers is clarified. Using self-compiled program, the SC generation in cascaded PCF
tapers with identical and different structural parameters are numerically simulated. Hence the function of cascading is
illustrated. Via cascading PCF tapers with same structural parameter, we can overcome the limitation of the tapering rig
to enhance the nonlinear interaction length. Via cascading PCF tapers with different structural parameter, we can not only
enhance the interaction length, but also obtain higher nonlinearity and more manageable dispersion to increase the
qualities of SC, such as spectral range and flatness.
Research on output characteristics of continuous-wave operation of Ho:YAG laser pumped by Tm:YLF laser
Show abstract
It report a continuous wave Ho:YAG laser pumped by1.91 μm Tm Laser. It important to thesis
analyzed the output characteristics of Ho laser pumped by continuous Tm laser.The rate equation of Ho
laser in continuous-wave operation was put forward. The rate equation was solved to analyze the
influence of upconversion effect to the output power, slope efficiency and threshold power in CW
operation .The transition branching ratio between the energy levels was taken into consideration while
discussing the influence of up conversion.Through the simulation analysis on the output characteristics,
consider the influence of upconversion effect than to ignore the influence of upconversion effect, The
threshold power increased by 0.34W, the highest output power of the reduced 2.89W, the slope
efficiency was decreased by 16.1%.Respectively,For all the experiments, the Tm:YLF laser crystal
keeps 292K and the temperature control method is water cooling. When we applied L shape plano
concave resonator, the length of the resonator is100mm, the radius of curvature output mirror is
150mm and the temperature of theHo:YAG laser crystal is 292K, we observed the central laser
wavelength is 2.09μm. The highest output power reaches 8.23W when the totally input pump power
is18W. And the slope efficiency is 45.7%, respectively. The experimental results are coincide with the
theory.
Directly writing embedded optical waveguides in LiNbO3 by a femtosecond laser
Show abstract
We have fabricated waveguides in z-cut Lithium niobate using focussed femtosecond pulses inscription of the bulk
material. The form of modified regions and their relationship with writing pulse energy and scan speed is examined.
Comparison of different methods for stripping cladding light in the high-power fiber laser
Show abstract
Different methods for stripping cladding light in the high-power fiber laser have been presented. Original fluoroacrylate jacket of fiber selected 50mm-length is continuous removed, then use three different index polymers recoated the selected section to make the uniform light stripping possible. The power-handling capability of the device is
tested over 140W cladding light, attenuation of 15dB is achieved and the local temperature does not exceed 70°C.
Optical fiber polarization control system based on fast locating algorithm
Show abstract
In this thesis, the currently feedback control algorithms used in the polarization controller, including
simulated annealing algorithm and gradient algorithm were analyzed. On this basis, a new method of polarization
control feedback algorithm based on fast locating algorithm was proposed to solve the defects of the original algorithm,
such as poor convergence and long time consuming search. It can reduce convergence time and improve the response
speed of the polarization controllers. This new endless polarization control algorithm using 4-plate polarization
controller was proposed and demonstrated. The results showed that the response time of the polarization controller was
less than 1ms. The control of polarization was achieved and the output polarization state was stable while the light
intensity fluctuated less than 2%, which could run endless reset freely.
Flexibly controllable multi-pulse mode-locked MOPA Yb-doped fiber laser in all normal dispersion regime
Show abstract
A Controllable, high energy, all normal dispersion (ANDi), passively mode-locked Yb-doped fiber laser is demonstrated with a Master Oscillator Power-Amplifier (MOPA) structure. The mode-locking is achieved by nonlinear
polarization evolution (NPE). different types of laser pulse are achieved from fundamental mode-locked (FML) single
pulse to twin pulse and then to harmonically mode-locked (HML) pulses (the maximum order is 7 times) by adjusting
quarter-wave plates (QWPS) and a half-wave plate (HWP) in our system. Using a cascaded long-period fiber grating as the spectral filter, the center wavelength of our laser is fixed at 1034nm.The repetition frequency rate of the FML pulse is
1.53MHz with a pulse width of 817ps. The maximum average energy is 450 mW and the maximum pulse energy of FML single pulse is 294 nJ. Besides, the 517nm green laser output is also achieved by using a LiB3O5 (LBO) crystal as
the frequency doubling crystal. The maximum average of the green pulse is 4.71mW.
Influence of the 400mm-aperture Nd:glass slab-amplifier gain nonuniformity on 1w(1053nm) near-field performance
Show abstract
optical propagation simulation by SG99 code and invert algorithm has been made for two typical laser architecture,
namely the National Ignition Facility (model A) and SG-III laser facility (model B) based on measured 400mm aperture
Nd:glass slab gain distribution data on ITB system. When the gain nonuniformity is about 5%, 7%, and 9% respectively
within 395x395mm2 aperture and output beam aperture is 360x360mm2, and output energy is about 16kJ/5ns(square)
with B-integral limited, 1ω(1053nm) nearfield modulation is about 1.10, 1.15, and 1.30 respectively for model A (11+7
slab configuration), and 1.07, 1.08, and 1.17 respectively for model B (9+9 slab configuration) without spatial gain
compensation. With the above three gain nonuniformity and slab configuration unchanged, to achieve flat-in-top output
near field, the compensation depth of the input near field is about 1.5:1, 2.0:1, and 6.0:1 respectively for model A, and
1.3:1, 1.4:1, and 3.5:1 respectively for model B. Compared with model A (the beam aperture unchanged in multi-pass
amplification), the influence of slab gain nonuniformity on model B (beam aperture changed) is smaller. All the above
simulation results deserve further experiment study in the future.
Enhancement of third harmonics generation during ultrashort pulse diffraction in multi-layer volume grating
Yizhou Tan,
Yisheng Yang,
Jiali Liao,
et al.
Show abstract
Successful phase-matching methods for Third Harmonics Generation (THG) include phase-matching in birefringent crystal and quasi-phase-matching (QPM) in crystal with periodically poled domains. However, these methods are not feasible in some isotropic materials (e.g. fused silica and photosensitive silicate glass). It was known that volume-grating in isotropic materials can independently generate frequency-converted waves. One of disadvantages of single-layer volumegrating is that the brightness of harmonic emission can not be enhanced by increasing the grating thickness. In this paper, a THG device with stratified sub-gratings was designed to enhance THG in isotropic materials: several sub-gratings were arranged parallel, and the grating-figures misalignment between neighboring sub-gratings was pre-fabricated. In terms of extension of interaction length in THG, our multi-layer sub-grating is formally equivalent to the multi-layer periodically poled crystal (e.g. lithium niobate) in conventional QPM approach. According to the calculation results, the N-layer (N <2) can, in principle, generate TH output intensity of N2 times stronger than single-layer volume-grating does, also compared to N times stronger than N-layer without figures-misalignment. The effect of random fabrication error in grating thickness on normalized conversion efficiency was discussed.
Modeling of 1.2-μm phosphorus doped Raman fiber laser
Show abstract
A model of 1.2μm Phosphorus doped Raman fiber laser is discussed. It is pumped by a 1.035μm high power
Yb-doped dual-cladding fiber laser. The coupled equations for forward and backward stokes waves are set up. An
approximate solution for the first –order Stocks laser is obtained by using ‘fsolve’ function in MATLAB which is simply
for writing and calculates fast. The relationships between energy conversion efficiency and the length of P-doped fiber,
the reflectivity of the output FLM are discussed respectively. And the laser system is optimized.
Design and preparation of frequency-doubled laser optical coatings for double wavelength with low waviness in short-wave
Huasong Liu,
Lishuan Wang,
Yugang Jiang,
et al.
Show abstract
Coating for double wavelength is one of the important elements in frequency-doubled solid state laser. In this paper, the normal design and whole numerical optimal design were compared. With the same total number of layers, the waviness of coating for double wavelength is more than 0.4139% based on normal design method, while it will be reduced to 0.0109% by whole numerical design, and also the bandwidth can reach 50nm. In experiments, the HfO2/SiO2 multilayer films were prepared by IBS. The test results of film designed by the
second method show that the transmissivity is above 99% at 532nm, waviness is 0.4%, and the reflectivity is
above 99.9% at 1064nm.
The study on the scaling relations between impulse coupling with aluminum by pulsed ultraviolet laser and by x-ray
Show abstract
In order to investigate the similarity on thermo-mechanical effects by different pulsed beams, this paper
conducts a comparison study on the blow-off impulse of aluminum target by pulsed ultraviolet laser and
X-ray irradiation. Especially, this paper focuses on the thermo-mechanical effects by pulsed ultraviolet laser
and X-ray (blow-off impulse), and build up the scaling relations of impulse coupling with aluminum target
by the two pulsed beams within a certain range of energy flux. The study shows that, within the energy flux
range of 100~400J/cm2, although the mechanisms of blow-off impulse generation of the two pulsed beams
are different, the impulse coupling with aluminum target or impulse coupling coefficients of both X-ray and
laser have similar scaling relations. Among others, the impulse coupling coefficient of X-ray is larger than
that of laser. Based on the comparison of scaling relations, this paper provides the similarity between the
two pulsed beams.
Passive coherent combination of all-fiber multichannel pulsed laser based on optical feed-back ring cavity
Show abstract
Self-organized passive coherent beam combination of multichannel pulsed laser with all-fiber configuration is reported.
The phase of multichannel Yb-doped pulsed fiber amplifiers is locked by optical feed-back ring cavity. The traditional
disadvantage of energy dissipation to side lode for lower aperture filling is solved via all-fiber laser array with
single-aperture configuration. Coherent beam combination of four pulsed fiber amplifiers is experimentally demonstrated.
Variable pulsed laser can be obtained by adjusting a AOM,stable combination pulsed fiber laser with excellent temporal
and spatial characteristic is achieved. The efficiency of coherent combination is up to 85.0%. This approach presented
here provides a feasible technique for power scaling of high-power pulsed fiber laser and maintaining beam quality
simultaneously.
High power Yb-doped fiber laser operates at special wavelength
Show abstract
Yb-doped fiber lasers (YDFL) have been one of the most widely studied project in last 10 years due to its
capability in high power output with excellent beam quality. The optical properties of Yb3+ ions in silica glass allow
lasing over wide spectral range from 0.98 to 1.2 μm. Up to now, most of the researches focus on YDFL lasing at
1.06-1.12μm, which is most common wavelength band. Actually YFDL operates at other special wavelength bands
(i.e., 1.17μm or 1.02μm) are widely required in many application fields. In this paper, we will reports the recent
research results of high power YDFL operates at special wavelength. By using Yb3+-doped double-clad silicate fiber
as the gain medium and commercial pigtailed laser diode as the pump source, we have demonstrated (1) an allfiberizied
YDFL operates at 1.12μm, a record output power of 178 W is obtained, the power is further boosted to be
309 W by using one stage of fiber amplifier (2) an all-fiberizied YDFL operates at 1.173 μm, a record output power
of 15.7 W is obtained when the pump power is 28 W. (3) an all-fiberizied YDFL operates at 1.018 μm, a record
output power of 309 W is obtained when the pump power is 435 W.
Linearly polarized operation of a Yb3+-doped double-clad fiber laser
Show abstract
In this work an all-fiber linearly-polarized Yb-doped double-clad fiber laser is proposed, in which the resonance cavity is
composed of a pair of polarization maintaining fiber Bragg gratings (PM-FBGs). The polarization hole burning is
enhanced by the selective polarization feedback by the PM-FBGs. A three-port polarization beam splitter with fiber
pigtail was inserted into the laser cavity to select different polarization states. The laser features wavelength of 1069.72
nm and 1069.98 nm, output power of 125 mW, SNR of 45 dB, slope efficiency of 52%, as well as linewidth of 30.7 pm.
The polarization characteristics of the laser are studied by measuring the laser power transmitted through a rotating Glan-
Thomson polarizer. The degree of polarization of each lasing line is over 12 dB under different pump levels.
Pulse multi-pass stretcher using linear chirped fiber Bragg grating
Show abstract
A pulse stretcher using chirped fiber Bragg grating is demonstrated. Pulses from a 1053nm mode-locked fiber seed
oscillator are multi-stretched by a Linear chirped grating set in a fiber regenerative amplifier structure. We have the pulse
stretched from 23.6ps to 378ps after it transmits 3 loops in the stretcher. The major factors which affect the stretched pulse
shape are discussed.
Deflagration-induced flash of solid pyrotechnics as pumps for high-energy solid state lasers
Xiaoli Kang,
Liming Liu,
Yongjian Tang
Show abstract
Using the flash produced by deflagration of solid pyrotechnics to pump the laser gain medium is a potentially
effective way to develop portable high power lasers. The purpose of this work is to examine the effect of some
optimization or modifications in terms of compositions and distribution of the pyrotechnic pumping sources on the laser
output. The optimization means the transmittance of the output couple. Modifications include: (1) pyrotechnic
compositions are improved by adding small amounts of nano Al powders; (2) distribution of pumping light around the
laser rod is changed through changing the discrete pyrotechnic tablets into continuous pyrotechnic bars. Results showed
that laser output energy reached the maximum of 656 mJ when the transmittance of output mirror raised to10%; after
adding nano Al powders into pyrotechnic compositions, laser energy increased by 80% at addition of 2% in the case of
discrete distribution, while in the case of continuous distribution, even the mass of pyrotechnics was halved, laser energy
still increased to the maximum of 442 mJ with 1% nano Al added. Besides, typical temporal waveform and spot of the
laser as well as the light radiation performance of the pyrotechnic tablet are measured to help analyze the laser output
performance. It is suggested that the mechanisms of the three modifications we employed are different though they all
lead to increase in laser output.
86 W continuous-wave diode side-pumped 1341.4nm Nd:YAP laser
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In this paper, we present a compact 803 nm diode side-pumped Nd:YAP laser that can produce 86 W of polarized
1341.4 nm output in continuous-wave mode. The laser characteristics including thermal lens and different cavity
types were studied. By comparing the output powers at different resonator lengths and different output couplers, 86
W output power with c-axis polarized laser at 1341.4 nm has been obtained at the maximum pumping power of 840
W. The optical-optical efficiency is 10.2% and the slope efficiency is 16.6%. The beam quality factors of the 1341.4
nm laser are 13.26 and 13.54 in the parallel and perpendicular directions, respectively.
Thermal blooming of different waveform laser propagation in atmosphere
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Based upon the scalar wave equation and the equations of hydrodynamics, the simulation model used to
calculate the transient thermal blooming of collimated multi-pulse laser by four-dimensional code. Considering the
variety of absorption coefficient along with different altitudes, this paper got the new model of repetitively pulsed
laser with thermal blooming in tropic by interpolation .On this basis, thermal blooming of different waveforms,
such as triangle, gauss, and rectangle were calculated. The paper analyzes the thermal blooming of three waveform
laser beams by changing respectively the value of the transmission power. After propagating the same distance in
the same condition, the result shows that the peak irradiance of triangular laser distorts least severely; the PIB of
gauss laser is the biggest, that is to say, the focusing ability of gauss laser is the best; the center of rectangle laser
moves the furthest.
High temperature operating (>80oC) 795-nm VCSEL based on InAlGaAs MQWs active region
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Design of the active region and analysis of temperature sensitivity of high-temperature operating 795-nm special
VCSELs for Chip-Scale Atomic Clock (CSAC) are presented. Composition and thickness of the InAlGaAs multiple
quantum wells (MQWs) are optimized at room and elevated temperatures. Temperature sensitivity of the threshold
current is analyzed by calculating the temperature dependence of cavity-mode gain over a broad temperature range
(25°C-150°C). A self-consistent VCSEL model based on quasi 3D finite element analysis is employed to investigate selfheating
effects and temperature distribution in the proposed structure. Output power of 2.5mW is expected from 10μm
aperture VCSELs at 10mA current at ambient temperature of 358K.