The laser pulse should be shaped to satisfy the ICF physical requirement and the profile should be flattened to increase the extraction efficiency of the disk amplifiers and to ensure system safety in ICF laser facility. The spatial-temporal distribution of the laser pulse is affected by the gain saturation, uniformity gain profile of the amplifiers, and the frequency conversion process. The pulse spatial-temporal distribution can’t be described by simply analytic expression, so new iteration algorithms are needed. We propose new inversion method and iteration algorithms in this paper. All of these algorithms have been integrated in SG99 software and the validity has been demonstrated. The result could guide the design of the ICF laser facility in the future.
Integration-Test-Bed(ITB) is China's first laser devices with single-beam ten-thousand joules output for Inertial Confinement Fusion (ICF) research. In this paper we describe the development of single-segment slab amplifiers for Integration-Test-Bed (ITB) with 400mm× 400mm aperture. The experiment results shows that the average small signal gain coefficient in 400mm×400mm aperture reach 5.28%/cm with the gain uniformity is about 1.09:1(maximum value/ average value), and up to 1.063:1 (maximum value/ average value) in 360mm×360mm beam-diameter clear aperture. The storage efficiency of system is about 1.47%. The pump-induced wave-front distortion is 5.3λ for the laser beams, which within the correction range of deformable mirror; the thermal recovery time was less than 4 hours. All of this guaranteed the output of 19.6kJ/5ns with wavelength of 1053nm from the Integration-Test-Bed (ITB) device.
The target position system (TPS) is one of the important subsystems of an ICF laser facility. However, TPS shows to have kinematic coupling problem in practice. This necessitates iterative adjustment of the Stewart 6-DOF manipulator to make the pose of the target as expected. In every iteration, the pose of the target must be measured, making TPS incompetent in some scenarios which call for only one step to position a target. To handle this problem, this paper proposes a target positioning method focusing on translational kinematic coupling. This method have a significant advantage that it has no relation with both the geometric parameters and the mounting of the target. This makes the proposed positioning method featured by a good practicality. Experiment results show that the proposed method can greatly reduce the position error when positioning a target by only one step.
A multi-beam alignment method is proposed to reduce the total time for aligning at the target area all the laser beams of an ICF laser facility. A number of sub-areas with invariant size and position are extracted from the image acquired by the alignment sensor. An alignment route is comprised of a certain part of those sub-areas, and several alignment routes can cover all the sub-areas. The invariant layout of the sub-areas and the alignment routes is called an invariant sub-area configuration of the alignment sensor. The focused spots of the alignment beams are adjusted in a specific sequence along the alignment routes, and finally reach the desired position on the alignment sensor. The adjustment of all the spots inside each sub-areas is carried out concurrently, and the adjustment along one route for a spot moving from one sub-area into the next sub-area is carried out consecutively. The estimated total time for aligning all the laser beams at target area shows that the proposed multi-beam alignment method has a much higher efficiency.
Backward Raman amplification (BRA) in plasma has been demonstrated an effective way to produce high power laser pulses. However, most experiments of BRA are carried out around the pump wavelength of 800 nm. In recent years, the 1053 nm pump pulse becomes more and more essential as the development of the chirped pulse amplification (CPA) around this wavelength. Here we design an experiment of BRA with a 1053 nm, 20 ps pump pulse and a 1200 nm, 50 fs seed pulse based on the facility of XG III. The simulation results obtained by a 1-d particle-in-cell (PIC) code show that the amplified peak seed intensity of ∼ 5 × 10<sup>16</sup> W/cm<sup>2</sup> is obtained, with an energy transfer up to 16.8%. An output pulse of petawatt power is theoretically demonstrated feasible.
The thermal problems of CPS and YDF were studied. And the thermal management technologies are developed separately to the problems. Experimental results showed that the thermal management technologies worked well.
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/cm<sup>2</sup> 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.
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 395x395mm<sup>2</sup> aperture and output beam aperture is 360x360mm<sup>2</sup>, 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.
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.
In ICF laser driver, the technique of precise target locating and guiding with multiple-beam is the core technique to
couple beams and target on experiments. Its performance superiority will decide operation success or failure of the
experiment on the whole facility. This paper will describe basic configuration of multiple-beam guiding and target
locating system in detail, emphasize on the technique route, which makes the whole system to carry out the full closed
loop control guiding beams and auto program process of shooting target, and makes the system shooting preparation time
less than 30 minutes and shooting accuracy better than 30μm (RMS). The technique is successfully applied on
ShenGuang-III prototype facility for two years.
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.
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.
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.
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 Ti:sapphire laser system referred to as SILEX-I with the chirped pulse amplification technology has been built at CAEP which consists of three stages operating at 5TW, 30TW, and 300TW, each having a compressor and target chamber to meet different needs from diverse applications. The first and the second stages work at 10Hz, while the third at single shot. Pulse durations of 26fs have been obtained by installing an acousto-optic programmable dispersive filter (AOPDF) before the stretcher to compensate for the spectral gain narrowing in the regen. By taking a number of advanced measures for spatial beam control, such as spatial beam-shaping, relay-imaged propagation, precise alignment of compressor gratings and OAP, near-diffraction limited focal spots (FWHM) have been obtained. Focused intensities
are measured in the range of (1-5) x 10<sup>20</sup>W/cm<sup>2</sup> with an f/2.2 OAP. The laser system will be able to operate at 500TW and even higher soon. The SILEX-I has been operated for experiments since its completion early in 2004, covering electron and proton acceleration, hot electron production, transport and deposition, neutron production, x-ray radiation, femtosecond laser pulse propagation in air, warm matter, and other strong-field studies. The laser system has shown an excellent stability and reliability and has been the most powerful femtosecond Ti:sapphire laser facility to operate for experiments in recent years.
A peak power of 286-TW Ti:sapphire laser facility referred to as SILEX-I was
successfully built at China Academy of Engineering Physics, for a pulse duration of 30 fs in
a three-stage Ti:sapphire amplifier chain based on chirped-pulse amplification. The beam
have a wavefront distortion of 0.63μm PV and 0.09μm RMS, and the focal spot with an
f/2.2 OAP is 5.7μm, to our knowledge, this is the best far field obtained for high-power
ultra-short pulse laser systems with no deformable mirror wavefront correction. The
peak focused intensity of ~1021W /cm2 were expected.
In conceptual design of the prototype for SG-III facility, a full aperture electro-optical switch was placed between the cavity mirror and the main amplifier to isolate the reflected beams. The beam on the cavity mirror is 240mm×240mm square. Pockells cells of conversional design with coaxial ring electrodes can not scale to such large square aperture. In the 1980s, a plasma electrode Pockels cell (PEPC) concept was invented at LLNL. It uses transparent plasma electrode formed through gas discharge as the electrodes to apply the voltage across switching crystal to rotate the polarization of a transmitted laser beam. And it can be scaled to large aperture with thin crystal. So the switch which would be used in SG-III is based on this technology. The technical integration line as a prototype of SG-III laser is actually a 4×2 beam bundle. And the full aperture optical switch is mechanically designed four apertures as a removable unit, and electrically two 2×1 PEPC putting together. So we built a 2×1 PEPC to develop the technology first. The 2×1 PEPC is a sandwich structure made of an insulating mid plane between a pair of plasma chambers. The frame of both plasma chambers are machining in duralumin. Each chamber is installed with a planar magnetic cathode and four segments spherical anodes made from stainless steel. The cathode and anode are insulated from the housing with a special shell made from plastic, and plasma is insulated from the housing by an 80-μm-thick anodic coating on the duralumin. The two plasma chambers are separated by a mid plane of glass frame with two square holes. The two holes are filled by two electro-optical crystals with a 240-mm square aperture. With the optimized operating pressure and the electrical parameters, a very good homogeneity and low resistivity plasma electrode is obtained. Finally we tested its switching performance to simulate the case that it will be used in the SG-III prototype facility. It works with a quarter wave delay voltage and the laser beam passes through PEPC twice. The average switching efficiency across the entire aperture is greater than 98.6%, the rising time of the switch is about 83ns, and the transmission of the switch is 86%.
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.
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.
Proc. SPIE. 5627, High-Power Lasers and Applications III
KEYWORDS: Diffraction, Optical amplifiers, High power lasers, Solid state lasers, Laser beam propagation, Adaptive optics, Near field, Wave propagation, Beam propagation method, Laser systems engineering
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.
We have built a three-stage Ti:sapphire laser system at CAEP which could deliver 5-TW, 30-TW and 286-TW pulses to the corresponding target chambers for diverse applications with innovative high-power Ti:sapphire crystal amplifiers. Pulse durations of 30fs have been obtained by installing an acousto-optic programmable dispersive filter (AOPDF) before the stretcher to compensate for the spectral gain narrowing. By taking a number of advanced measures for spatial beam control, near-diffraction limited focal spots (FWHM) have been obtained which, to our knowledge, are the best far fields ever measured for the existing high-power Ti:sapphire laser systems without deformable mirror correction. Focused laser intensity is about 10<sup>21</sup>W/cm<sup>2</sup> measured with an f/1.7 OAP. The laser system has the potential to operate at 500TW and even higher and laser intensities of 10<sup>22</sup>W/cm<sup>2</sup> are expected with deformable mirror for wavefront correction and small f-number fine OAP for tighter focus added to the system in the near future.
A multihundred-terawatt Ti:sapphire laser facility was built at China Academy of Engineering Physics which could deliver femtosecond pulses at three power levels of 5TW, 30TW and hundreds TW to targets. Near-diffraction-limited focal spots were measured and it was found for the first time that alignment errors of grating groove parallelisms in compressors could be the major mechanism for producing elongated far fields. Pulse durations of 35fs were obtained with a Fastlite-produced AOPDF for spectral compensation.
To measure the temperature and density of electronics in laser plasma accurately, two probe laser systems are built on XG-II laser facility. The one, called UV probe laser system, which can provide the UV laser pulse with duration of 30 ps by cascade Raman compressor after fourth harmonic conversion is used for density measurement of laser plasma. The other one, Thomson scattering system, which can provide the 4 ω laser pulse with energy of 3 - 5J, is now routinely operated for electronics temperature diagnostic in laser plasma. It is the first time that the density and temperature of laser plasma are measured directly by probe laser at the same shot.
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.
Intense lasing at 18.9, 20.3 and 28.5 nm from nickel-like molybdenum, niobium and neon-like chromium ions has been observed by using two 200 ps laser pulses with a total energy of 50 J at 1.053 micrometers from XingGuang II laser facility. This shows the possibility of extending nickel- like and neon-like x-ray lasing in low-Z elements and paves the way towards small scale x-ray lasers for applications at university laboratories. A comparison has been made of performance of the neon-like chromium soft x-ray lasing at 28.5 nm driven by a double 900 ps pulse at 6 TW(DOT)cm<SUP>-2</SUP>, with that driven by a double 200 ps pulse at similar irradiance. The double 200 ps pulse has been found to be more efficient to drive the neon-like x-ray lasing.
Development plan and some progress have been made for amplifier of SGIII laser facility. According to this plan, a single-segment amplifier has been designed and experimented to test key units and correct simulating code in National Laboratory of Laser Fusion of China. The preliminary design for 4 X 2 X 3 amplifier prototypes, including amplifier modules, pulsed power, assembly equipment, and optics for SGIII will be finished.
A ray tracing method for design of geometrical arrangement of laser beams in target area is described in this paper. A mathematically mode for path's design are suggested to minimize the objective functions f<SUB>j</SUB>(R<SUB>i</SUB>, L<SUB>i</SUB>, (alpha) <SUB>i</SUB>, (beta) <SUB>i</SUB>), which are the optical length difference between the real path length from laser amplifier to the target center and the design objective path length. And the constraint conditions for beam's path are as follows: (1) Beams illuminate the cylindrical target with the incident angles required for the physical experiments. (2) 60 beams propagate without overlapping each other, and each of them with equal optical length from the laser amplifier to the target center. (3) Bema incident to the reflection mirror P<SUB>i</SUB> with the decided angle (phi) <SUB>i</SUB>, for example, value of (phi) <SUB>i</SUB> is less than or equal to 45 degrees for all paths, and etc. Mathematical methods, such as 'Depth First Search technique', or searching optimum point for objective function f<SUB>j</SUB>(R<SUB>i</SUB>, L<SUB>i</SUB>, (alpha) <SUB>i</SUB>, (beta) <SUB>i</SUB>) with constraint conditions are stated. Design examples are reported, in which the 60-Gaussian beam are symmetrically distributed around the target chamber.
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.
A computer code has been developed and simulations have been conducted to design the target area optical layout according to the requirements of both the physical and the SG-III laser facility itself for both direct and indirect drive configurations, respectively. The number and location of the required 240 turning mirrors from the output lens of the transport spatial filter to the target chamber have been initially decided, and the mechanical interventions of optical paths have also been solved.
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/cm<SUP>2</SUP> 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 30cm<SUP>2</SUP>, 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.
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.
This paper aims at the request of dividing harmonic waves in the high power laser system used to perform Inertial Confinement Fusion. Dividing harmonic waves is realized by introducing binary optical element. Based on scalar diffraction theory, the distribution of its diffraction field was calculated and the fabrication parameters were also optimized. The element is fabricated with RIE. We also measured the relief structure and diffraction efficiency of each harmonic wave and analyze the errors.
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.