KEYWORDS: Structural design, Control systems, Control systems design, Crystals, Fusion energy, Kinematics, Turbulence, Safety, Lithium, National Ignition Facility
This paper first studies the structure effect law in order to design a reasonable option in theory for the Final Optics Assembly(FOA)’ harmonic converter module, involved in the design of the fluid theory, including the basic equations of fluid motion, the form of fluid motion and fluid movement in the small hole. Optimizing the structure need to be applied to the simulation software, which requires the Fluent simulation principle. Then, combined with theoretical knowledge to design the overall structure of the multiplier module, It will apply the simulation software to optimize structural parameters of the board and use control system to realize it for verifying the law obtained by simulation under various conditions whether consistent with the law in actual work of the sweeping system.
Experimental research on non-critical phase-matching fourth harmonic generation with ADP and DKDP crystals are reported. The characteristics of 2ω-to-4ω efficiency as function of incident angle, crystal temperature and input 2ω intensity have been investigated in detail, and the 2ω-to-4ω conversion efficiency has been demonstrated up to 84.1% with ADP crystal and 85.1% with DKDP crystal, respectively. Nevertheless, the spatial non-uniformity of rapid grown DKDP crystal has to be improved while the temperature control uniformity should be upgraded for ADP crystal to realize large aperture high efficiency fourth harmonic generation.
KEYWORDS: Picosecond phenomena, Kinematics, Laser welding, Physics, High power lasers, Laser systems engineering, Current controlled current source, Systems modeling, Modeling, Matrices
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.
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.
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.
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.
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.
We report a novel frequency tripler for efficient conversion of broadband high power laser pulses at 1 μ;m. The tripler is
composed of several segmented partially deuterated KDP with discrete values of deuteration. Deuteration level can be
used as a degree of freedom to alter the phase-matching wavelength of a partially deuterated KDP crystal. The
segmented partially deuterated KDP crystal is made by thermal bonding method. It has been shown that this new tripler
is capable of enhancing the acceptance bandwidth of frequency tripling. A two-segment design is presented, which is
applicable to the efficient frequency tripling of chirped pulses with a bandwidth of ~1.2-nm.
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.
The design of the Large Laser Facility incorporates a type-I-type-II third harmonic generator to convert the 1.053μm fundamental wavelength of the laser amplifier to a wavelength of 0.351μm for target irradiation. To understand the design of frequency conversion system, we have carried out a series of theory researches and experiments, including parameters optimization of the third harmonic converter, experiments on high-intensity third harmonic generation (THG), researches on Transverse Stimulated Raman Scattering (TSRS) in the converting crystal and on broad-band third harmonic generation.
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