This paper comprehensively considers the suppression effect of fiber parameter control on Stimulated Brillouin Scattering (SBS), and studies the influence of different phase modulation modes, different linewidths, different fiber Yb ion densities, and different fiber lengths on the SBS threshold of the whole system, The best system setting scheme for improving SBS threshold is also given.
The coherent beam combination of kW fiber lasers with a filling aperture has been in research. An experiment is set up to achieve the coherent beam combination. The coherent beam combination of two fiber lasers with a filling aperture is realized, and the phase bandwidth of the beam combination is measured and analyzed. The laser spots before and after the combination are detected respectively. The phase noise of high power laser is measured and the factors affecting the phase noise are analyzed.
The stimulated Brillouin scattering (SBS) effect in fiber amplifiers using white noise signal (WNS) phase modulated seed is simulated. The influences of cut-off frequencies of WNS and the output fiber structure on SBS threshold are discussed. Basing on simulation results, optimized phase modulation signal and output fiber structure are achieved to suppress SBS. A fiber laser is established according to the simulation results.
An all-fiber system based on the principle of optical waveguide self-imaging for coherent beam combination (CBC) system is designed. A square fiber is used as the beam combination device for all-fiber CBC system. The self-imaging characteristics of the square fiber are studied. The self-imaging effect of the square fiber is verified by theoretical simulation and experiment. The square fiber has good self-imaging characteristics and is suitable for CBC using its self-imaging characteristics.
To ensure sufficient absorption of tandem-pumping energy, a large-scale aluminophosphosilicate fiber with 55 μm core and 400 μm inner-clad in diameter, i.e., a 55/400 Yb-APS fiber, was experimentally fabricated by using modified chemical vapor deposition system combining with chelate precursor doping technique. Based on an all-fiberized master oscillator power-amplifier laser setup tandem-pumped by 1018 nm fibber laser, a 150 W 1080 nm seed was amplified to 11.18 kW successfully, along with an optical-to-optical efficiency of 79.7%.
In this paper, the model to simulate the impact of bend induced mode distortion on the beam quality and mode instability (MI) threshold of fiber amplifier is established, and the results show that the bend induced mode distortion will degrade the beam quality of fiber laser and decrease the MI threshold. The bend induced mode distortion will change the gain of active fiber, then destroy the beam quality of fiber amplifier, and decrease the MI threshold, but the bend loss will suppress high order mode. Therefore, with the decreasing of fiber bend radius, the MI threshold will decrease firstly, and then increase.
The design of annular doping region located in the cladding can reduce signal overlap with the doped region in order to reduce saturation and minimize gain compression, which has important applications in EDFAs. Here, we present the design and power scaling characterization of a cladding-pumped amplifier with ytterbium dopant located in an annular region near the ultra low NA core in the cladding, which is found to be a promising way to achieve multi-kilowatt single mode fiber lasers. The ultra low NA ensures that the fiber amplifiers operate in single mode state, which results to that the fiber amplifiers are free of the limitation of the transverse mode instability, and that the mode field of the signal laser extends into the cladding to extract gain amplification. The annular ytterbium-doped region located in the cladding can overcome the contradiction between high doping concentration and ultra-low NA design, which can simultaneously obtain high pump absorption with ultra low NA. The size of annular ytterbium-doped region under different core NA has been studied for various core sizes, which shows that the optimal size of annular ytterbium-doped region is related to the core NA and the core size. Detail analysis of high power amplification of cladding-ring-up-doped ultra low NA single mode fiber amplifier has been presented, which includes various nonlinear effects and thermal effects. It shows that, due to the specific design, the single mode characterization of the fiber is less influenced by the detrimental thermo-optic effect, which means that the cladding-annular-doped ultra-low NA fiber has high mode instability threshold than the ultra-low NA fiber with the core being fully uniformly doped. The cladding-pumped fiber amplifiers based on cladding-annular-doped ultra low NA fiber has the capability to achieve >10kW single mode fiber lasers.
We fabricated and reported a pedestal fiber with Yb/Ce-codoped aluminosilicate (Al2O3-SiO2) core and germanosilicate (GeO2-SiO2) pedestal. This newly-optimized chelate precursor doping technique enables us to make homogeneous large-core pedestal fiber with strong pump absorption from Yb3+ ions about 3.66dB/m at 915nm. The fiber core was homogeneously doped with 4450ppm Yb3+, 11600ppm Al3+ and 1800ppm Ce3+, and surrounded by pedestal layers with 25000ppm Ge4+. The results indicate all-gas-phase chelate precursor doping technique is highly competitive for the fabrication of pedestal fiber towards narrow-linewidth fiber laser.
A direct diode-pumped all-fiber-integrated fiber laser based on backward pumping master oscillator power amplifier configuration at 1080 nm, producing maximum output power of 4.115 kW based on 25/400 μm fiber with corresponding linear fitting optical to optical efficiency of 78.39% was demonstrated. The suppression ratio of stimulated Raman scattering is better than 35dB and it can be further optimized by decreasing the seed input power. Near diffractionlimited beam quality (M2 are 1.7and 1.6 in the x and y directions based on 4-sigma method) is also achieved at the maximum output power. To the best of our knowledge, this is the first report for 4 kW near-diffraction-limited fiber lasers based on 25/400 μm fiber directly pumped by laser diodes.
In this manuscript, a 3.53kW average output power all-fiber laser system at 1064nm with 3dB linewidth as narrow as 0.16nm and near single-mode beam quality (M2 ≈1.7) is demonstrated. There is no obvious stimulated Brillouin scattering, stimulated Raman scattering or amplified spontaneous emission observed. To the best of our knowledge, this is the highest output power of all-fiber laser system with narrow-linewidth and near single-mode beam quality ever reported.
Thulium-doped fiber laser is one of the most promising high power mid-infrared sources which attracts lots of attention recently. However, there is no comprehensive theoretical model which can be used for precise simulation of the performance of the pulsed Thulium-doped fiber laser. A combined theoretical model is proposed in this work by integrating the laser rate equation and Ginzburg-Landau equation into the iteration process. Good agreement between the experiments and simulations is achieved in a Thulium-doped fiber amplifier employing counter-pumping scheme.
To investigate the laser performance of Ce/ Yb-codoped aluminosilicate (Al2O3-SiO2) binary glass fiber, we took commercial Nufern-20/400-9M fiber as a research object. 0.95 kW laser output power at 1066 nm with an optical-to-optical efficiency of 83.3% was achieved at fiber laser amplifier stage. Beam quality of Mx2 and My2 is 1.56 and 1.68 at 0.95 kW, respectively. The results indicate Nufern-20/400-9M fiber may be suitable
Transverse mode instability becomes the main limit for power scaling of high power fiber lasers with nearly diffraction-limited beam. Compared to conventional step index fiber, this paper proposes a partially doped fiber, which can decrease coupling coefficient between fundamental mode and higher order mode. Based on a coupled mode model, this designed fiber is proved to suppress transverse mode instability effect and promising for power scaling of fiber lasers. Furthermore, we investigate the impact of doped region on transverse mode instability threshold, and propose a partially doped fiber, which can realize 5 kW in single mode regime theoretically.
A high power 1030 nm ytterbium-doped polarization maintained fiber laser with optimized parameters is presented in this paper. The master oscillator power amplifier system with counter-pumped amplifier is established. The output power is 900 W, along with a light-to-light efficiency of 64.2%. The amplified spontaneous emission suppression ratio of spectrum reaches to 40 dB with 3 dB linewidth of 0.14 nm. The polarization extinction ratio is 12 dB, and the beam quality factor is M2x=1.07, M2y=1.12. To the best of our knowledge, this is the first demonstration of 1030 nm high power fiber laser with narrow linewidth, near linear polarization, and neardiffraction-limited beam quality
Based on a master oscillator power amplifier configuration, laser performance of commercial Nufern-20/400-8M Ybdoped aluminophosphosilicate ternary laser fiber was investigated. Pumped by 976 nm laser diodes, 982 W laser output power was obtained with a slope efficiency of 84.9%. Spectrum of output was centered at 1066.56nm with 3dB bandwidth less than 0.32 nm, and the nonlinearity suppression ratio was more than 39dB. Beam quality of Mx2 and M2y were 1.55 and 1.75 at 982 W, respectively. The laser performance indicated that Nufern-20/400-8M Yb-doped aluminophosphosilicate ternary laser fiber is highly competitive for industry fiber laser use.
Transverse mode instability (TMI) limits power scaling of fiber lasers. A semianalytical model is established to calculate the TMI threshold in high-power fiber laser systems of the multi-kW-class. A linear inner-cladding fiber can mitigate the TMI effect by smoothing the heat profile and decreasing the nonlinear coupling coefficient along the fiber. We investigate strong pump absorption of a linear inner-cladding fiber, which leads to shorter fiber length. Utilizing a 915-nm copumping scheme, the linear inner-cladding fiber can realize 10-kW output power in single-mode regime theoretically.
A new architecture of four pass amplification system for main amplifier stage of ICF driver was tested with I x2 amplifiers in the aperture of 240x240mm2. A compact plasma-electrodes Pockels cell(PEPC) was first adopted in beam reverser. The preliminary experiment results testified this architecture and provided a approach to build big laser drivers.
The coherent amplification network (CAN) aims at developing a laser system based on the coherent combination of multiple laser beams, which are produced through a network of high beam quality optical fiber amplifiers. The scalability of the CAN laser facilitates the development of many novel applications, such as fiber-based acceleration, orbital debris removal and inertial confinement fusion energy. According to the requirements of CAN and the front end of high-power laser facilities, a millijoule polarized fiber laser system was studied in this paper. Using polarization maintaining Ytterbium-fiber laser system as the seed, and 10-μm core Yb-doped fiber amplifier as the first power amplifier and 40-μm core polarizing (PZ) photonic crystal fiber (PCF) as the second power amplifier, the all-fiber laser system outputs 1.06-mJ energy at 10 ns and diffraction limited mode quality. Using 85-μm rod-type PCF as the third power amplifiers, 2.5-mJ energy at 10-ns pulse width was obtained with better than 500:1 peak-to-foot pulse shaping ability and fundamental mode beam quality. The energy fluctuation of the system is 1.3% rms with 1-mJ output in one hour. When using phase-modulated pulse as the seed, the frequency modulation to amplitude modulation (FM-to-AM) conversion ratio of the system is better than 5%. This fiber laser system has the advantages of high beam quality, high beam shaping ability, good stability, small volume and free of maintenance, which can be used in many applications.
We use a semi-analytical model considering pump power saturation in high power fiber laser systems of multi-kW-class to calculate mode instability threshold. A novel designed fiber, linear inner-cladding fiber, can mitigate mode instability effect by decreasing nonlinear coupling coefficient and smoothing heat profile along the fiber. We investigate strong pump absorption of linear inner-cladding fiber, leading to shorter fiber length. With 915 nm pumping, linear inner-cladding fiber can reach 10 kW output power without mode instability in theory.
Chirp pulse amplification (CPA) has been promoted as an effective way to explore the intensity frontier. High order dispersion induced by the stretcher and materials in the CPA system, which deteriorates both the pulse duration and temporal contrast, however, can not be absolutely compensated by the compressor. Placed at the Fourier plane of a 4f zero-dispersion stretcher consisting of a grating, the deformable mirror (DM) has been demonstrated as the modulator to compensate high order dispersion. Using the method of ray tracing, the relation between spectrum and position on DM has been obtained. It shows that the resolution of the deformable mirror can be controlled by adjusting the focal length and incident angle. We have simulated a typical Ti:sappire CPA system to revise the spectral phase by the DM. The result illustrates that if the spectral phase can be compensated, the temporal contrast will be improved by 2 order of magnitude.
KEYWORDS: Wavefronts, Adaptive optics, High power lasers, Beam controllers, Control systems, Wavefront distortions, National Ignition Facility, Mirrors, Sensors, Wavefront aberrations
Experiment of entire beam wavefront compensation was carried out in a beamline of a high power laser facility, and two adaptive optics systems with different intentions were applied in the chosen beamline. After correction, the far-filed irradiance distribution is concentrated evidently and the entrance rate of 3ω focal spot to a 500-μm hole is improved to be about 95% under number kilojoules energy.
KEYWORDS: Sensors, High power lasers, Coherent beam combination, Signal detection, Research facilities, Numerical simulations, Beam splitters, Automatic control, Process control, Calibration
Array element tiling is one of the key technologies for the coherent beam combination in a high-power laser facility. In this paper, we proposed a method of the array element auto-tiling based on capacitive displacement sensor. The method was verified on a double-pass tiled-grating compressor in XG-III laser facility. The research showed that the method is an effective way to control the misalignment errors automatically, with high precision and long-term stability.
The paper presents the technical design and progress on a special high-power laser facility, i.e. XG-III, which is being used for high-field physics research and fast ignition research. The laser facility outputs synchronized nanosecond, picosecond and femtosecond beams with three wavelengths, i.e. 527 nm, 1053 nm and 800 nm respectively, and multiple combinations of the beams can be used for physics experiments. The commissioning of the laser facility was completed by the end of 2013. The measurement results show that the main parameters of the three beams are equal to or greater than the designed ones.
KEYWORDS: Optical amplifiers, Spatial filters, Diagnostics, Near field, Frequency conversion, Glasses, Near field optics, Laser systems engineering, Laser applications, Crystals
The Integration Test Bed (ITB) is a large-aperture single-beam Nd:glass laser system, built to demonstrate the
key technology and performance of the laser drivers. It uses two multipass slab amplifiers. There are four
passes through the main amplifier and three passes through the booster amplifier. The output beam size is
360mm by 360mm, at the level of 1% of the top fluence. The designed output energy of ITB at 1053nm is
15kJ in a 5ns flat-in-time (FIT) pulse, the third harmonic conversion efficiency is higher than 70%. The first
phase of the ITB has been completed in July 2013. A series of experiments demonstrated that laser
performance meets or exceeds original design requirements. It has achieved maximum energies at 1053nm of
19.6kJ at 5ns and 21.5kJ at 10ns. Based on a pair of split third harmonic generation KDP crystals, the third
harmonic conversion efficiency of about 70% and 3ω mean fluences as high as 8.4 J/cm2 have been obtained
with 5ns FIT pulse.
SG-III laser facility is now the largest under-construction laser driver for
inertial confinement fusion (ICF) research in China, whose 48 beams will deliver 180kJ/3ns/3ω energy to target in one shot. Till the summer of 2014, 4 bundle of lasers
have finished their engineering installation and testing, and the A1 laser testing is
undergoing. A round of physics experiment is planned in Oct. 2014 with 5 bundle of
lasers, which means the facility must be prepared for a near-full-capability operation
before the last quarter of 2014. This paper will briefly introduce the latest progress of
the engineering and research progress of SG-III laser facility.
The under-construction SG-III laser facility is a huge high power solid laser driver, which contains 48 beams and is
designed to deliver 180kJ energy at 3ns pulse duration. The testing ending up at September 2012 validated that the first
bundle lasers of SG-III facility had achieved all the designed requirements. And shortly later in December 2012, the first
round of running-in physics experiment provided a preliminary X-ray diagnostic result. In the testing experiment,
detailed analysis of the laser energy, the temporal characteristics, the spatial distribution and the focusing performance
was made by using the Beam Integrated Diagnostic System. The 25kJ 3ω energy produced by the first bundle lasers
created the new domestic record in China. These great progresses in the laser performance and the physics experiment
have already demonstrated that the facility is in excellent accordance with the designs, which establish a solid foundation
for completing all the construction goals.
This paper is focused on the research of SSD and CPP carried out on TIL. A bulk phase modulator with 9.2-GHz modulation frequency is adopted in SSD. The output spectrum of the phase modulator is stable and the residual amplitude modulation is small. FM-to-AM effect caused by free-space propagation after using smoothing by spectral dispersion is theoretically and experimentally studied. Results indicate inserting a dispersion grating in places with larger beam aperture alleviates the FM-to-AM effect, suggesting minimizing free-space propagation and adopting image relay. Experiments indicate when the number of color cycles (Nc) adopts 1, imposing of SSD with 4.26 times diffraction limit (TDL) did not lead to pinhole closure in the spatial filters of the preamplifier with 20 TDL and main amplifier with 26 TDL. Experimental results also indicate SSD didn’t influence the load capacity of the laser facility. The contrast of the 440-μm diameter focal spot with 95% energy included using SSD and CPP drops to 0.47, comparing to 1.71 not using SSD and CPP. When the pulse width of the third harmonic wave is 1 ns and the energy is 1115 J, no damage is found in CPP and other final optics. The experiments solves some key technical problems using SSD and CPP on high-power laser facilities, and provides a flexible platform for the laser-plasma interaction experiments.
The multi-pass amplified scheme of SGII upgrading laser is similar as that of NIF. Large aperture plasma electrodes Pockels cell (PEPC) is the key unit of this amplified scheme. The transit time that laser beam passes through the PEPC for the first time and second time is about 270ns. PEPC should switch the state between ON and OFF in 270ns. The response time of the PEPC driven by positive-negative switching pulses can not satisfy the demand of SGII upgrading laser due to the higher generator impedance. In the single-pulse-process, the low-impedance high voltage generator based on double Blumlein pulse-forming line is used to drive the PEPC. The amplitude of single pulse is up to 21kV, while the impedance of the generator is only 6.25Ω. The theoretical charge time of the PEPC with 350mm×350mm aperture is about 54ns, and the response time of PEPC is less than 170ns in the single-pulse-process. The response time is reduced greatly. The switching efficiencies with full aperture are higher than 99.7%. The extinction contrast exceeds 381. The top width of the time window is larger than 160ns, and the bottom width is about 400ns. All the experimental results can meet the specification of SGII upgrading laser.
With the methods of time-division multiplexing in Frontend and angle detuning in FOA, each beam pulse on SG-III
prototype facility is controlled independently and so the systematic variations of power imbalance are eliminated
entirely.
Development of a phased-array-grating compressor is a crucial issue for high-energy ultrashort pulse petawatt lasers. To achieve tiled array gratings and increase stability of tiled-grating frames, a new tiled grating frame is designed. In the tiled-grating frame, an integrated support structure is adopted to increase the natural frequency of the tiled-grating and the flexible hinges are used rather than the spring to increase the joint stiffness between the grating and the support frame. The experiment indicates that stability of the tiled-grating can be maintained for more than 1 h and the standard deviation of the tiling error is 35.7 nm, which satisfies the design requirement.
The influence of laser beam size on laser-induced damage performance, especially damage probability
and laser-induced damage threshold (LIDT) is investigated. It is found that damage probability is beam
size dependent when various damage precursors with different potential behaviors are involved. This
causes damage probability and LIDT are different between tested under large-aperture beam and under
small-aperture beam. Moreover, fluence fluctuations of large-aperture laser beam bring about hot spots
moving randomly across the beam from shot to shot. Thus it leads to the most probable maximum
fluence after many shots at any location across components is several times the average beam fluence.
These two effects result in difference of damage performance of components in large-aperture lasers
and in small-aperture lasers.
The stability of phased-array optics is a crucial issue for far-field focal-spot quality. The tiled approach of phasing optical elements is a widely used technique. Here it is adopted to maintain the long-time stability of a tiled system by a proportional-integral-differential (PID) algorithm. Experimental data is taken with 2×1 tiled-flat square mirrors driven by 3-axis piezoelectric actuators. The feedback frequency is over 80 Hz and the displacement error is below 4 nm. The optical measurement results show that the state-locked operation is continuously maintained for hour-long periods in PID control mode.
To meet the needs of some physical experiments for high energy short pulse laser, TGC (tiled gratings compressor)
technology and beams-combination technology are required. Progress of TGC and beams-combination at CAEP is
introduced. On TGC technology, interference pattern and far field distribution is used to initially eliminate the tiling
error, and displacement sensor is used as feedback to maintain the posture of the sub-gratings. As for beams-combination
a preliminary method of feedback control in subsections is proposed and will be expected to be used in an integrated test-bed.
Plasma Pockels cell (PPC), which can use a thin crystal to perform the uniform electro-optical effect, is ideal component
as average-power optical switch with large aperture. In this paper, by reformative design and employing a capacity to
share the gas discharge voltage, the DKDP PPC driven by one pulse is realized. As gas breakdown delay time is stable,
and discharge plasma is uniformly filled the full aperture, it meets the demand of plasma electrode for the repetition-rate
PPC with DKDP crystal. A rep-rate plasma Pockels cell (PPC) with Φ30mm aperture has been fabricated. It is optimized
with the limited space of repetition rate diode pumped laser. The specification of the PPC is: static transition of 97.2%,
switching efficiency of 99.8%, the switch rising time of 8.6ns. In the LD pumped Yb:YAG plate laser system, the PPC
can steadily work on 10Hz repetition rate performed as Q-switch. The key problems in PPC are analyzed for
repetition-rate application, and thermo-optical effects are simulated by means of numerical modeling when average
power laser is loaded on the electro-optical crystal. Furthermore, the principium design of rep-rate PPC with
longitudinally conductive cooled structure is described in this paper. It will efficiently abate the thermo-optical effects
under repetition rate application.
Laser induced damage experiment was carried out on a large aperture laser facility. Severe damage has
been observed on a large-aperture fused silica grating which presented dense craters on the front
surface and six cracks alternatively located at the front and the rear surface. The bizarre fact about the
damage on the grating is that, unlike other optics, the damage craters are almost on the front surface.
According to observation, damage phenomenon is due to the Stimulated Brillouin Scattering (SBS)
effect happened in the grating.
Laser-induced damage is a key lifetime limiter for optics in large laser facilities. After tested on a
large-aperture high-power laser facility, a damaged fused silica component is disassembled and
conditioned to receive damage test on a small-aperture laser. The damage threshold and growth
behavior show the corners on the component are less damage resistant. The acid etch on corner has not
effectively increased the damage threshold but lowered the damage growth coefficient. A
statistic-based model is presented to extrapolate the threshold data in small-aperture test to predict the
damage threshold under functional conditions.
A novel method has been proposed to suppress transverse stimulated Raman scattering or transverse
stimulated Brillouin scattering by processing the frequency convector edges into arrises. The mode
analysis indicates that the residual reflection at the edges decreases rapidly with the decrease of arris
angle and the direction of the ray finally reflected back has an angle with the surface of convector. So
with this method transverse stimulated Raman scattering or transverse stimulated Brillouin scattering
can be suppressed.
A novel method based on diffraction theory to control the far-field irradiance profile by deformable mirror is presented.
Special near-field phase which determines the contour of the focal spot is obtained by a high spatial frequency
deformable mirror. Numerical simulations show that, we can control the far-field intensity envelope as CPP by
adopting adaptive optics technique when the spatial resolution of deformable mirror is high enough, here 16×16
actuators in 320mm×320mm aperture. The coupling coefficient is an important factor influencing control effect, and
its best value range is round 0.6.
Large-aperture plasma Pockels cell is one of important components for inertial confinement fusion laser facility. We
demonstrate a single-pulse driven PPC with 350mm×350mm aperture. It is different to the PPC of NIF and LMJ for its
simple operation to perform Pockels effect. With optimized operation parameters, the PPC meets the optical switching
requirement of SGII update laser facility. Only driven by one high voltage pulser, the simplified PPC system would be
provided with less associated diagnostics, less the maintenance, and higher reliability.
KEYWORDS: Optical amplifiers, High power lasers, Fiber amplifiers, Prototyping, Solid state lasers, Mirrors, Laser development, Near field, Integrated optics, Fusion energy
We are currently developing a large aperture neodymium-glass based high-power solid state laser, Shenguang-III
(SG-III), which will be used to provide extreme conditions for high-energy-density physical experiments in China. As a
baseline design, SG-III will be composed of 48 beams arranged in 6 bundles with each beam aperture of 40cm×40cm. A
prototype of SG-III (TIL-Technical Integration experimental Line) was developed from 2000, and completed in 2007.
TIL is composed of 8 beams (four in vertical and two in horizontal), with each square aperture of 30cm×30cm. After
frequency tripling, TIL has delivered about 10kJ in 0.351 μm at 1 ns pulsewidth. As an operational laser facility, TIL has
a beam divergence of 70 μrad (focus length of 2.2m, i.e., 30DL) and pointing accuracy of 30 μm (RMS), and meets the
requirements of physical experiments.
Damage inspection of the large aperture components is required for Large, high-power laser systems. Dark-field
imaging technology is used to enhance resolution of defects. Because there are several of the optics which are laid with
Brewster angle in optics online inspection and the image collected by CCD includes many noises, so the image are quite
complex. A kind of image processing method is introduced, which is based on classical method about edge detection.
Gray restrain is used and the relations between the pixel and its eight neighbours are considered in calculating the
gradient. The defect size is measured and damage defect of optics is analyzed using the image processing methodology.
The new approach produces nice result.
KEYWORDS: Physics, Sapphire lasers, Optical amplifiers, Laser systems engineering, High power lasers, Laser applications, Solid state lasers, Near field optics, Crystals, Lawrencium
High-power solid-state laser programs at China Academy of Engineering Physics have made great progresses in recent years. A three-stage Ti:sapphire laser system, SILEX-I, was completed early in 2004 which could deliver 26-fs pulses at 5TW, 30TW, and 300TW to the corresponding target chambers for diverse applications. SILEX-I has been working very stably since its completion for experiments, demonstrating that it is the most powerful femtosecond Ti:sapphire laser for exploring strong-field phenomena in the world. The SG-III Nd:glass laser facility has been under conceptual design to meet the requirements from laser fusion applications. The SG-III facility is planned to have sixty-four beamlines divided into eight bundles with an output energy more than 100kJ at 0.35μm for 3- to 5-ns pulses. The eight-beamline TIL (Technical Integration Line), the prototype of the SG-III laser facility, has been installed in the new laboratory in Mianyang. The commissioning experiments have been conducted and one of the eight beams has produced 1-ns pulses of 3.0kJ and 1.2kJ at 1.053μm and 0.35μm, respectively. All the eight beamlines will be activated by the end of 2005 and completed in 2006 for operation. Meanwhile, the eight-beam SG-II laser in Shanghai Institute of Optics and Fine Mechanics has been operated for the experiments since 2001 and an additional beam, built in 2004, has been used for plasma backlighting experiments.
A theoretical approach, based on the paraxial wave equation and the Fresnel integral, are presented to investigate nonlinear hot-image formation of an intense laser beam. Fresnel-zone-plate-like hologram induced by the sum of a wave scattered from a small scatterer and a background wave produces the negative first order diffracted wave (conjugative wave) that is focused to an traditional hot-image, and the negative second order diffracted wave that develops to an intense second-order hot-image. It is seen by the analytical results that the two images may attain a high intensity level enough to damage optical components in high-power lasers, showing that these two images should be equally taken into account for large lasers optimization of system design.
We are now constructing a technical integration experiment line (TIL) at CAEP, which is the prototype facility of Shenguang III laser fusion driver. Currently, many important results have been obtained on the first integrated beam line, which established a sound foundation for Shenguang III engineering design.
KEYWORDS: Optical amplifiers, Near field, High power lasers, Solid state lasers, Adaptive optics, Beam propagation method, Wave propagation, Diffraction, Laser systems engineering, Laser beam propagation
The characteristics of linear propagation and amplification of pulse in the high-power solid-state laser system were analyzed. The decomposition of linear propagation of the different parts in this system was also made. And the controlling means for beam quantity were put forward. At the same time, the measured near field and far field of the beam in TIL (Technical integrated experiment line, the prototype of SGIII (the Laser facility for ICF in China) were discussed, which proved these means were valid. These results of the theoretical analysis and experiment research become the general idea for investigating the problem of linear propagation in this system.
In this paper, the physical models of the code SG99, which is used to simulate the pulse behavior in high power laser system, are presented in details. The experimental results are also presented to show that SG99 is capable of simulating pulse propagation well and yields reasonable results. In the last, some results in design of TIL(Technical Integrated Experiment Line), the prototype of ShenGuangIII, are also introduced.
A ray tracing software has been developed to allocate the stability requirements of a fusion laser facility. Using the developed software and by establishing a mathematical model of the layout of the fusion laser facility TIL, the task of analyzing the relations between the stability of any individual optical component and the position of the beam foci on the target has been fulfilled. Then, by adding random perturbation to the coordinate parameters of all optical components of the facility and calculating the possibility of the foci to locate in the sphere with radius of 30 μm (the target-shooting requirement of TIL), the stability requirements of the components of the facility has been acquired.
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.
High power solid state laser technologies for application to inertial confinement fusion have been developed over the past three decades in China. The XG-1 laser facility was built in 1984 and upgraded into XG-II in 1993. The SG-1 was completed in 1985 and the upgrade into SG-II will be finished in a few months. As the next step, the SG-III laser facility has been proposed to produce 60-kJ blue light for ICF target physics experiments and is one being conceptually designed. A preliminary baseline design suggest that he SG- III be a 64-beam facility with an output beam size of 25 cm X 25cm. The main amplifier column of 4 high by 2 wide has been chosen as a module. New laser technologies, including multipass amplification, large aperture plasma electrode switches, fast growth of KDP, laser glass with fewer platinum grains, Ce-doped quartz long flash lamps, capacitors with higher energy density, Ce-doped quartz long flash lamps, capacitors with higher energy density and precision manufacturing technique of large optical components have been developed to meet the requirements of the SG-III Project. In addition, numerical simulations are being conducted to optimize the optical design of the facility. The technical integration line with a 4 X 2 segmented aperture array of the amplifiers as a prototype beamline of the SG-III has been scheduled for the next few years.
In this paper, we present the preliminary design of Technical Integration Line (TIL). TIL is a full scale 4 X 2 module of Shenguang-III (SG-III). laser facility with a two-aperture output of 3.0kJ at 3 (omega) in a temporally shaped pulse of 1.0-3.0 ns. The goal of TIl is to demonstrate the laser technology of the proposed SG-III. TIL consists of front-end, pre-amplifier stage, main amplifier stage, diagnostic target systems and control system and the average fluency is designed to operate at 5.0J/cm2 in a 1.0 ns output pulse. The optical scheme of a four-pass main amplifier and a booster amplifier have been chosen. The clear aperture of amplifier is 30 X 30cm2, and the numbers of Nd:glass disks in the two amplifiers are optimized in system design. Two spatial filters are inserted in the system to remove high spatial frequencies from the beam, and SF1 is the multi-pass spatial filter and SF2 is the transport spatial filter. In order to correct the output wavefront for static and dynamic wavefront aberrations of disk amplifiers, a deformable mirror system is used in the main amplifier stage of TIL.
A four pass amplifier system with a small aperture beam reverser has been designed as the main amplifier stage of Technical Integration Line (TIL). TIL is the full scale two- beam prototype for Shenguang-III laser facility which will produce 1 kJ of UV radiation on the target from each beam in 1-3 nanoseconds shaped pulses. The variables were optimized for a fixed output beam aperture of 25 X 25 cm2 and the given parameters of the optical components under the constraints of amplifier gain, fluency damage/filamentation and so on. As a result, the baseline design for TIL was set to a 9-5 configuration.
The ICF Programs in China have made significant progress in solid state laser technology development and advanced laser facility designing with multilabs' efforts in the past years. The eight-beam SG-II laser facility is expected to complete for a 4.8-kJ output at 1.05 micrometers and to operate for target experiments in a few months. A national project, SG-II laser facility, has been proposed to produce 60-kJ blue light for target physics experiments and is being conceptually designed. New laser technologies, including multipass amplification, large aperture plasma electrode switches, fast growth of KDP, laser glass with fewer platinum grains, long flash lamps and precision manufacturing of large optical components are being developed to meet the requirements of the SG-III Project. In addition, numerical simulations are being conducted for the optical design of the new facility. The Technical Integration Line of 4 by 2 segmented array as a prototype module of SG-II with a chamber for laser beams measurements will be first built in the next few years.
The spatial filters are used in Technique Integration Line, which has a multi-pass amplifier, not only to suppress parasitic high spatial frequency modes but also to provide places for inserting a light isolator and injecting the seed beam, and to relay image while the beam passes through the amplifiers several times. To fulfill these functions, the parameters of the spatial filters are optimized by calculations and analyzes with the consideration of avoiding the plasma blow-off effect and components demanding by ghost beam focus. The 'ghost beams' are calculated by ray tracing. A software was developed to evaluate the tolerance of the spatial filters and their components, and to align the whole system on computer simultaneously.
Technical Integration Line (TIL) is the full scale two-beam prototype for Shenguang-III laser facility. A four pass amplifier system with small aperture beam reverser has been designed as the main amplification stage for TIL, which will produce 1 kJ of UV radiation on the target from each beam in 1-3 nanoseconds shaped pulses. Two schemes were considered in the preliminary design, one of them employed only small aperture Pockels cell in the reverser, and the other used another larger plasma electrode Pockels cell in the main beam line. Simulated by a fast-running lumped-element computer code, the configuration of baseline scheme for TIL was settled. The basic requirements for optical elements were raised during simulation processing.
A new design of a multipass amplification system which adopt stimulated Brillouin scattering (SBS) phase conjugation mirror is presented in this paper. By application of active SBS mirrors and four-color laser beams, this system has the potential ability on pulse shaping and beam smoothing for target uniform illumination. The preliminary simulation result shows this 7-disk amplifier system will generate 1.5 kJ 3(omega) pulses.
The concept of a three-pass amplification system was developed. There was no large aperture Pockels cell and polarizer in the system. A special beam transformer was adopted to ensure the beam match and diminish self-oscillating in the cavity by insertion of a small size optical switch. Some preliminary simulation results are given to optimize the design.
An accurate method for measuring charge transfer efficiency (η) and photoresponse nonuniformity (PRNU) of linear charge-coupled devices is developed. The apparatus is described. A finely focused light spot is adopted to irradiate each photosensitive element to get its response output signal. Data are collected automatically by scanning peak-searching and processed by linear best fitting. As examples, measurements for some types of devices are reported and factors influencing the results are discussed.
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