A 1319 nm single frequency nanosecond pulsed laser based on injection seeded is demonstrated. The laser oscillator is injection seeded by a 1319 nm single-frequency narrow linewidth Nd:YAG nonplanar ring oscillator (NPRO), a laser pulse of repetition rate of 500 Hz, pulse energy of 2.3 mJ, pulse width of 70 ns, and jitter of <3 ns is obtained based on ramp-hold-fire resonance detection technology. Then, through a four-stage end pump laser amplifier, the pulse energy is amplified to 15.4 mJ, with a beam quality factor of M2<1.5.
An 885nm LD end-pumped burst-mode laser with high repetition frequency and low thermal effect is introduced in this paper. The laser can solve the problem of high repetition frequency and high energy in the traditional continuous pulse output mode, and can meet the requirements of light source of airborne lidar well. The laser adopts the main oscillating power amplification (MOPA) structure. The oscillating stage uses 885nmLD pulse pumped Nd:YAG crystal, which can reduce the thermal power consumption of the laser. The electro-optic Q-switch is used for intra-cavity modulation, and the output pulse train with a repetition frequency of 4Hz, each pulse train contains 60 sub-pulses with a repetition frequency of 1kHz.Finally, the fundamental frequency light with central wavelength of 1064nm, sub-pulse repetition frequency of 1kHz, single pulse energy of 6.1mJ and beam quality is obtained. In the amplification stage, 885nm end-pumped Nd: YAG crystal was used. After one-way amplification, the laser output with sub-pulse energy of 15.7mJ, pulse width of 12ns and beam quality was obtained.
In this work, we investigate the SBS mitigation of the pseudo random bit sequences (PRBS) modulation analytically and numerically. The lightwave is phase modulated by a Butterworth lowpass filtered and amplified PRBS signal, and the SBS suppressing capability versus the parameters such as the filter order, the filter cutoff frequency, the modulation depth, and the pattern length are illustrated. Therefore, we redefine the modulation depth by normalized RMS voltage to integrate binary sequences modulation signal and multi-value sequences modulation signal. On this basis, we demonstrate the impact of pattern length, modulation depth and modulation cutting rate on SBS mitigation and found the corresponding optimal component of n=9, 22.72 dBm and 0.54. On this situation, contrast to the unfiltered PRBS phase modulation scheme, a 17.7% enhancement of normalized SBS threshold can be obtained by using normalized power in the barrel to estimates the linewidth. This work may provide a new idea for SBS mitigation by lowpass filtered PRBS phase modulation in narrow linewidth fiber amplifiers.
A Nd:LuAG disk laser with V-shape stable resonator and active-mirror configuration, end-pumped by 808 nm laser diode array, is demonstrated. By using a theoretical model, performances and optimization of the disk laser is investigated theoretically and experimentally. A maximum output energy of 4.5 J per pulse operating at 10 Hz repetition rate is obtained for the laser with the optimum output coupler transmission of 15%, the corresponding optical-to-optical efficiency is 18.8%. It proves that Nd:LuAG ceramic active-mirror disk laser is a promising alternatives for high-energy lasers.
In this paper, we investigated the association between beam quality and beam characteristic in theory in a spectral beam combining system and built a model to describe the dispersion. We analyzed that how the beam quality varies with different input beam parameters such as the waist radius 𝑤𝑤0 and the spectral width Δλ. There is a surprising result that the increased w0 and Δλ have a coefficient influence on the beam quality degradation, and the degradation is pretty sensitive to the increase of waist radius w0. The result gives us a guidance that besides using the narrow linewidth laser, we also need reduce the waist radius of the input beam in the SBC system appropriately to abate the beam quality degradation caused by dispersion.
Our study describes the development of coherent beam combining of an array of nine fiber lasers using an all-optical ring cavity feedback loop based on a diffractive optical element to achieve a single-aperture output. Nine 300-mW Yb-doped fiber amplifier beams arranged in a 1 × 9 end-cap array were combined to achieve a single-aperture beam with a power of 739 mW and a beam quality (M2) of 1.18 with 21.5% combining efficiency. The optical spectra, far-field distributions, and time-domain characteristics of the combined beams were investigated under open- and closed-loop conditions. Under open-loop conditions, the far-field coherent visibility changed constantly from 72.1% to 90.9% and the fluctuation intensity was strong. Under closed-loop conditions, the system achieved a steady state with a visibility of 98.6% and an average feedback intensity of 0.4 V, indicating the occurrence of phase locking. Furthermore, mode hopping was observed when there were more than four channels in a combination. However, the system interference pattern remained stable. Comprehensive research on the relevant literature indicated that novel filled-aperture CBC was achieved using an all-optical ring cavity feedback loop based on a DOE.
Diffractive optical element is used to realize single-aperture output for passive coherent combining of 8-channel fiber laser. Using this system, we demonstrated the far-field coherent visibility, output spectrum and beam quality after coherent combining. Experimental results show that phase noise will cause the mode frequency to change under multi-channel conditions. However, the beam quality and the coherent visibility after coherent combination do not change significantly. The far-field coherence visibility reached 98.6%, the beam quality M2=1.21, and the diffraction limit magnification factor β reached 1.98. This shows that in the presence of low phase noise, even if the number of channels is increased, a coherent combined output with high beam quality can be obtained.
Coherent polarization beam combining (CPBC) is an effective method to obtain a high-brightness laser with linear polarization state. In this paper, we propose a method to apply optical heterodyne detection to CPBC. An optical phase modulation is implemented to transform the phase difference of two beams to amplitude modulation for polarization state detection. The CPBC of two lasers with the same frequency is realized by linear proportional-integral-derivative (PID) phase-locked control. Based on this principle, a three-channel CPBC system is realized to obtain a linearly polarized output beam with a high PER. The PER obtained in the experiment reached 17.44 dB with the output power of 431 mW, while the control bandwidth is 66.1 kHz. The residual phase noise of the first-stage CPBC system achieved to 1×10-4 rad/ √Hz at 1 Hz and 4×10-6 rad/ √Hz for more than 100 Hz.Compared with other CPBC phase-locking methods, this method can effectively suppress phase noise and has a significant improvement in control bandwidth and polarization extinction ratio.
In this study, the total deviation of central diffracted beams caused by the periodic projection effect and refraction of zero-order diffracted beam of diffractive optical element was theoretically investigated. The theoretical model of the relationship between the total deviation of central diffracted beams and the combining angle of the ith order incident beam was developed. Inversely, the total deviation of central diffracted beams can be used to calibrate the actual combining angle of the ith order incident beam, further guide the correction of the actual combining angle in coherent beam combining.
We investigated the beam quality improvement of a tiled-aperture coherent beam combining by changing the intensity distribution of fiber beamlets array. An optimal gradient power distribution of the beam array is found. The beam quality is improved by 12.6% with a fill factor of 0.5 with gradient distribution architecture compared with the uniform distribution. With the expansion of the array scale, the improvement of beam propagation factor is becoming more obvious. In addition, the effects of phase error and beamlet arrangement layout are also researched, which shows the propagation factor of the hexagonal ring arrangement is improved by 16.14% compared with the ring arrangement under the gradient arrangement. The effect of phase error on the combined beam quality with respect to the gradient distribution is discussed.
Aimed to maintain excellent beam quality, the influence of pointing deviation on the beam quality is theoretically studied in the dual-grating spectral beam combination (SBC). The incident light field of the fiber laser array with the pointing deviation is built by the transformation of coordinates, and the variation rule of the combined beam quality with random perturbations is discussed by the principle of beam diffraction and the statistical analysis. As a result, the degradation of beam quality for the pointing deviation is respectively 0.31(±0.13) and 3.06(±1.27) for the standard deviation of 0.1 mrad and 0.5 mrad, spreading as a Normal distribution. It can be concluded that the pointing deviation of laser array will destroy the condition of the SBC of the common aperture output, resulting in the continuous growth of the M2 factor. These analyses provide a valid basis for setting up the experimental system of dual-grating SBC.
To suppress high order modes and improve the beam quality, an active self-imaging mode filter based on multimode interference and self-imaging effect is proposed in large mode area (LMA) fiber amplifier. With this filter structure, transverse mode competition and individual transverse mode power distributions in strongly pumped fiber amplifiers are theoretically demonstrated. Employing this mode selection technique in 30/400 LMA strongly pumped fiber amplifier, the percentage of the fundamental mode rises from 27.8% (without filter) to 96.3%. By the modal power decomposition, the M2 parameter of beam quality decrease dramatically from 2.24 to 1.11 (0 relative phase) and from 3.01 to 1.24 (π/2 relative phase). This study provides a new method to achieve single mode in LMA fiber amplifier and this filter would be extended to larger mode area fiber amplifier to improve the beam quality.
1-MW peak power picosecond, 574-kHz repetition rate green laser at 515-nm is generated from a frequency-doubled fiber amplifier. 12-ps pulses with 13.9-μJ energy at 515 nm are achieved with a noncritically phase-matched lithium triborate (LBO) crystal through second harmonic generation of a 1030 nm infrared source. The infrared source employs ultra-large-mode-area rod-type photonic crystal fiber (Rod-PCF) for direct picosecond amplification and delivers 20-W 11.6-ps 2.97-MW pulse train with near-diffraction-limited beam quality (M2 = 1.01).
A tunable dual-wavelength passively mode-locked thulium-doped fiber laser (TDFL) based on single-wall carbon nanotube is demonstrated. By properly tuning the pump power and the polarization controller, both single- and dual-wavelength mode-locked operation can be achieved. The repetition rates of the single- and dual-wavelength mode-locked operation are both 17.64 MHz. The duration of the ultrashort soliton pulse is about 3.7 ps. By appropriately adjusting the polarization state of the laser, the dual wavelength can be tuned from 1879.8 and 1894.5 nm to 1903.3 and 1914.1 nm.
We have demonstrated a kW continuous-wave ytterbium-doped all-fiber laser oscillator with 7×1 fused fiber bundle combiner, fiber Bragg grating (FBG) and double-clad gain fiber fabricated by corresponding technologies. The results of experiment that the oscillator had operated at 1079.48nm with 80.94% slope efficiency without the influence of temperature and non-linear effects indicate that fiber components and gain fiber were suitable to high power environment. No evidence of the signal power roll-over showed that this oscillator possess the capacity to highest output with available pump power.
In this paper, we demonstrate an ytterbium-doped all-fiber master-oscillator power amplifier (MOPA) system which uses a narrow-linewidth seed source, generating narrow-linewidth and high power continuous-wave output power at 1064nm. Our MOPA configuration system consist of three amplifier stages. We use single-mode Yb-doped fiber as the gain fiber in the first and second pre-amplifier stages, so it can keep good beam quality before entering the main amplifier stage. In order to raise the threshold of nonlinear effects, such as SBS and SRS, and to relieve heat effect, our high power system choose large mode area (LMA) fiber as the gain fiber in the main amplifier stage. For the sake of suppressing high-order modes in LMA fiber, we design novel watering cooling plates of different sizes, and using them in our main amplifier stage. By optimizing its structure, we get very good laser beam pattern on CCD at high power output. The beam quality factor (M2) was about 1.4 at 1.31 kW.
The effect of surface morphology on laser-induced crystallization of hydrogenated intrinsic amorphous silicon (a-Si:H) thin films deposited by PECVD is studied in this paper. The thin films are irritated by a frequency-doubled (λ=532 nm) Nd:YAG pulsed nanosecond laser. An effective melting model is built to identify the variation of melting regime influenced by laser crystallization. Based on the experimental results, the established correlation between the grain growth characterized by AFM and the crystalline fraction (Xc) obtained from Raman spectroscopy suggests that the crystallized process form amorphous phase to polycrystalline phase. Therefore, the highest crystalline fraction (Xc) is obtained by a optimized laser energy density.
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.
The laser performance of a short-length Yb-doped rod-type photonic crystal fiber (PCF) laser is studied experimentally both in the three-level scheme and quasi-four-level scheme in this contribution. In the free oscillation mode, the rod-type PCF laser produce 13.6 W output power on the quasi-four-level system with center wavelength of 1030 nm. The laser operating on the three-level system is obtained with the introduction of specialized feedback around the 976 nm radiation. Up to 7 W output power is generated with wavelength centered in 978 nm.
We demonstrate a passive coherent beam combination of two nanosecond amplifiers by using an all-optical feedback loop. An electro-optic amplitude modulator is utilized to tune the pulse width and the pulse repetition frequency of combined laser pulse. The positive correlation between the visibility of far-field coherent patterns and the pulse duty ratio is found. The range of tunable pulse repetition frequency is from 2.023 MHz to 6.069 MHz, and the range of tunable pulse width is from 10 ns to 50 ns. The maximum visibility is up to 85%. This approach presented here provides a promising way for power scaling of high power nanosecond fiber laser and maintaining beam quality simultaneously.
We demonstrated a passive phase locking of a seven-element 352 W all-fiber polarization-maintaining amplifiers array using an all-optical feedback loop. Every single channel has four-stage amplifiers and is seeded by a broadband master oscillator for stimulated Brillouin scattering free. The seven laser beams are tiled side by side into a hexagonal laser array with a high space duty ratio of 65% in the near field. When system is in closed-loop, a visibility more than 90% of coherent pattern in the far field is obtained. By using the all-optical feedback loop and more pump power, higher power scaling with high beam quality appears to be achievable in a coherent beam combination system.
A phase-shifted double pulse method is proposed to reduce the influence of inner-pulse interference induced fading on
phase demodulation of the Φ-OTDR. The feasibility of the technique is experimentally verified and the measurement
resolution of the Φ-OTDR is minimized to as low as 0.1rad by using this technique. The experimental system
demonstrates a distributed phase monitoring capability over 4km range with SNR of >20 and detection bandwidth
of >360Hz.
Laser-induced fluorescence (LIF) of high-purity fused silica irradiated by ArF excimer laser is
studied experimentally. LIF bands of the fused silica centered at 281nm, 478nm and 650nm are
observed simultaneously. Furthermore, the angular distribution of the three fluorescence peaks is
examined. Microscopic image of the laser modified fused silica indicates that scattering of the
generated fluorescence by laser-induced damage sites is the main reason for the angular distribution
of LIF signals. Finally, the dependence of LIF signals intensities of the fused silica on laser power
densities is presented. LIF signals show a squared power density dependence, which indicates that
laser-induced defects are formed mainly via two-photon absorption processes.
The inscription method of FBGs on large-mode-area double-clad fibers (LMA-DCFs) with phase mask technique was
described. A pair of LMA FBGs was prepared and the center wavelengths of them were both around 1076nm with 3 dB
bandwidths of about 0.5nm. The reflectivities of them are 99% and 10% in the fundamental mode, respectively. In order
to be protected and to withstand high-power laser, the FBGs were metally packaged, and then applied to an Yb3+-doped
LMA-DCF laser as the laser cavity. An output power of 314 W centered at 1075.71 nm with a slope efficiency of 60%
was achieved.
A master-oscillator fiber power amplifier system with a 4.5-m-long Yb3+-doped homemade large-mode-area double-clad fiber is reported. Up to 156 W average power of 1064 nm amplified pulse, corresponding to a slope efficiency of 64.9%, has been demonstrated. The amplified pulse possesses a pulse duration of 24 ns and a repetition rate of 50 kHz and demonstrates a good beam quality (M=2.81 and M=2.66), although no special transverse-mode-controlling techniques were adopted.
Based on the frustrated total internal reflection theory, a leaky large-mode-area double clad fiber is
designed. The propagation constants and leakage loss of the fundamental mode LP01 and sub-low order
mode LP11 is investigated by using of the matrix method. Results show that the designed fiber can
operate with single-mode.
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.
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.
Recent progress in the research of a diode pumped, single-frequency 355nm laser for direct-detection wind lidar is
presented. An injection seeded Nd:YAG laser was designed and built. A 'delay-ramp-fire' technique is used to achieve
single-longitudinal-mode and stable energy. In this technique, stable time relation between the resonance peak and the
pump pulse is achieved by feedback controlling the delay time between the pump pulse and the ramp voltage. The resulting
single frequency pulses are amplified and frequency tripled. This laser operates at 100Hz and provides 30mJ/pulse of
single-frequency 355 nm output with M2 value of <1.5. The frequency stability of the injection seeded Nd:YAG laser was
investigated. The piezo hysteresis is found to be the main reason to cause the frequency unstability. In an environment
avoiding high frequency vibration the frequency stability is determined by the motion linearity and ramping speed of the
piezo actuator. A modified approach is proposed to improve the frequency stability of an injection seeded laser.
A compact diode-pumped, injection-seeded and frequency- tripled Nd:YAG laser was developed for a mobile, direct detection Doppler wind lidar system. The laser is configured with the master oscillator power amplifier (MOPA). The oscillator consists of E-O Q-switched, thermal stability, diode pumped cavity. The oscillator is injection seeded by a monolithic, diode-pumped Nd:YAG seeder laser with power of 200mW. The technique of resonance detection is used to lock slave laser frequency in order to satisfy with the mobile environment. The output laser from oscillator is single-way amplified. Frequency triple is realized with a Type II KTP crystal and Type I BBO. The laser can be working on single frequency without mode jumping. The output pulse is about 15 ns at 355 nm, the linewidth is reached to the limit of Fourier transfer. The output energy is 100 mJ of 1064 nm at 100 Hz, and the beam quality is about M2 of 1.3 at both directions. The frequency- triple efficiency is over than 30%. After a long time test, the laser will be installed on a mobile lidar system.
KEYWORDS: Fizeau interferometers, LIDAR, Doppler effect, Sensors, Interferometers, Reflectivity, Laser stabilization, Signal detection, Wind energy, Signal to noise ratio
Fringe technique is preferred to edge technique of wind measurement in troposphere for a direct-detect Doppler wind lidar. However, most fringe-technique based Doppler lidar systems have been developed to date are based on conventional Fabry-perot interferometer. The purpose of this paper is to introduce our development of fringe-technique lidar based on Fizeau interferometer in which the signal can be detected more conveniently using commercial linear detector. The pre-development of the lidar system is described including interferometer's optimum design, the frequency stabilization of Fizeau interferometer and the choice of multi-anode detector. In additional, the wind error of the system is simulated with taking account of Rayleigh noise. Results shows that the wind error can be less than 0.56m/s under 5 km with 30s integral time.
Fiber Lasers are most powerful solid state lasers available for various applications, they are capable of providing diffraction, limited power with compact, efficient and cost effictive system. In this paper, we report a master, oscillator fiber power amplifier for pulsed operation from 20kHz to 100kHz. A 4m double cladding fiber has central core of 43um and inner core of about 600/650um is used as amplifier, the seed source is a pulsed laser with output power of 1 W at 1064nm. A fraday isolator protect the seed laser from backflection from fiber amplifier. The MOPA system is analysied by transient gain model, pulsed amplified characteristics of double cladding fiber are caulated and compared with experimantal results at different pumping power and repetition rate.The fiber amplifier is pumped by laser diode at wavelength of 795nm with pumping power of 230W, the system can emits average power upto 133.8 W with repetition rate of 100kHz.
Polycrystalline ceramic Nd:YAG laser material enables new possibilities in designing the laser medium
with respect to dopant, size and geometry. In this paper, a 184W continuous-wave Nd3+-doped ceramic
Y3Al5O12 (Nd : YAG) laser with optical to optical efficiency of about 44.3% has been developed. Laser output
power characteristics as well as the thermal lensing and birefringence properties of the ceramic laser rods were
investigated. The sample used in this experiment was a 3.5mm diameter, 87mm long ceramic YAG rod with
0.6% Nd3+ concentration. And the end faces of the rod were flat and antireflection-coated at 1064 nm. The
pumping geometry used in this work was a diffusive optical cavity with narrow slits for side-pumping.
A master-oscillator fiber power amplifier (MOPA) system with a 4-m-long Yb3+-doped homemade large mode area (LMA) double-clad fiber is reported. The system emits up to 133.8 W of amplified radiation at a wavelength of 1064 nm and a repetition rate of 100 kHz, limited only by the available pump power. Peak power of 300 kW at 20 kHz with a pulse duration of 15 ns is obtained.
A high power Ytterbium-doped fiber laser (YDFL) with China-made double clad fiber (DCF) is introduced in this paper. The Geometric parameter and laser characteristics of the newly designed fiber have been studied. When both ends of the fiber were pumped by two
high-power laser diode with the total lunched power about 600W , we got the laser output of 330W, with an optical-to-optical efficiency of 55%.
A direct-detection Doppler lidar for planetary boundary layer wind field measurement utilizing multi-beam Fizeau interferometer (MFI) is proposed. Fringe imaging and edge techniques are popular methods of incoherent wind speed measurement. In boundary layer, where aerosol backscattering is strong, it is good to measure wind velocity with fringe imaging technique. Fabry-Perot interferometers (FPI) are standard instruments in former incoherent lidar. Their performance is restricted from detector channels. However, linear fringes of MFI can be measured directly by linear detector, for example, charge coupled device (CCD). The MFI consists of two flat plates which assembled much like a FPI, but wedged by a small angle. Through three PZTs fixed on one plate, the plates spacing can be tuned and the wedge angle can be adjusted. The physical properties of the MFI are discussed in this paper. The factors affecting the measurement of Doppler frequency shift and the correction methods are analyzed and presented. A set of practical system parameters is proposed. The numerical simulation of system performance is implemented. Under different parameters of MFI, error of horizontal wind speed is compared in boundary layer. It shows that the error can be less than 1m/s using the optimized parameters of MFI.
A highly efficient Yb doped double clad fiber laser, one end pumped by a 975nm diode attack source and generating up to 115.6 of CW output power at 1100nm is reported in this paper, the maximum optical-optical conversion efficiency is 79% and the slope efficiency is about 69%. The frequency doubling of the fiber laser is obtained with conversion efficiency of 6% by using PPLN as nonlinear optical material.
The output characteristics of double cladding fiber laser are investigated pumped by 915nm and 975nm diode lasers. The average effective absorption coefficients for two kinds pump wavelengths are given. A 20W Ytterbium - doped fiber laser in 1110nm region with near diffraction limited beam spread angle are reported.
KEYWORDS: Fiber lasers, Ytterbium, Absorption, Cladding, Signal attenuation, Semiconductor lasers, High power lasers, Temperature metrology, Diodes, Mirrors
The wavelength characteristics of Yb3+-doped double cladding fiber are investigated pumping by 915nm and 975nm high power laser diode respectively. The relationship between the pumping power and pumping wavelength on laser output are measured and discussed in detail.
The fiber laser's excellent focus and efficiency, small size and light weight makes it highly promising not only for telecommunication, but also for industry and medical applications. In a double clad fiber laser, the inner cladding for guiding the pump light is provided around a core doped with active ion (e.g. YB3+, Nd3+, Er3+, etc.). The recent progress of fiber laser is reviewed at first in this paper. Different shapes of inner cladding are investigated to increase the pumping efficiency. Beam-shaping optics deliver high-power beams as the pumping source is discussed. Finally, a 4.9W cw double-clad fiber laser demonstration experiment in SIOM is described.
In this paper, We have proposed a new cross section shape of inner cladding benefited from the conception of unsteady cavity in laser technology. The absorption characteristic of this new type double-clad fiber is analyzed in detail with ray tracing method. For this new type and rectangular double-clad fibers, with core diameter 8im and pump area 100?mX 100?m, about 98% pumped propagation rays are absorbable after 100 times reflection in the inner cladding, so it is possible to achieve very high absorption efficiency. However, for circular, offset and D shape double-clad fibers, with same core diameter and pump area above, only 10%, 50%,80% pumped propagation rays are absorbable.
The SG-III laser facility has been proposed to produce 1-ns, 60-kJ blue light pulses for IC Application at China Academy of Engineering Physics. The baseline design suggests that the SG-III be a 64-beam laser facility grouped into eight bundles with clear optical apertures of 30cm by 30cm. The facility consists of multiple subsystems, including the front end, preamplification and injection section, main amplifiers, beam transport and alignment system, switchyard, target area, integrated computer control, and beam diagnostics. The amplifier column in each bundle contains eight beamlets stacked 4 high by 2 wide. Great progress has been made in developing key laser technologies, such as integrated fiber optics, binary optics, adaptive optics, four-pass amplification, large aperture plasma electrode switches, rapid growth of KDP, brand-new laser glass, long flashlamps, precision manufacturing of large optics and metallized self-heating capacitors. Codes have been developed and numerical simulations have been conducted for the optical design of the facility. The design of the Technical Integration Line of 2 by 2 segmented array as a prototype module of SG-II has been optimized and the construction will soon get started.
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