Xiaofeng Wei

Design of 60-kJ SG-III laser facility and related technology development

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.

The code SG99 for high-power laser propagation and its applications

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.

Parasitic oscillation suppression in high-gain solid-state amplifiers

A method has been proposed for suppressing parasitic oscillation by processing the gain medium edges into arrises. The mode analysis indicates that the residual reflection at the gain medium edges decreases greatly and the required index matching level and the required cladding absorbency are reduced as well. With this method, a large choice of edge cladding material is allowed, which can help with avoiding distortion and other problems caused by thermal stress.

ASE suppression in high-gain solid-state amplifiers by a leak method

A leak method was developed to suppress amplified spontaneous emission (ASE) in large-aperture high-gain solid-state amplifiers. The gain medium edges are processed into an arris. The ASE ray will undergo reflection several times at the arris surface when it propagates to the gain medium edges, and most of its power will leak out. This leak method was tested in an experiment, in which a piece of commonly used gain medium was processed for contrast. The maximal increase of the gain value was 5.26% with the maximal pump power.

Accurate measurement and control of delay variation between two ultra-short laser pulses based on cross-correlation

A method based on cross-correlation is proposed for measurement and control of accurate delay variation between two ultra-short laser beams. The accuracy can reach to a few femtoseconds.

Preliminary results of Ti:sapphire ultrahigh-power laser facility

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.

Measurement and control of micro-errors on components-tiling and beams-combination

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.

Suppression of transverse stimulated Raman scattering or transverse stimulated Brillouin scattering

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.

Generation of broad-bandwidth femtosecond 270-nm light by third-order nonlinear coupling with focusing beams in a single crystal of BBO

By third-order nonlinear coupling and tightly focusing the beams in a single crystal of BBO, high intensity broad-bandwidth femtosecond pulses are used to generate 50&mgr;J of light at 270nm (up to 1% THG efficiency). And it is proved that the major contribution to the THG observed is the third-order process, not the cascaded second-order process.

The art for broad-bandwidth direct third-harmonic generation focusing beams in a single crystal of BBO

By third-order nonlinear coupling and tightly focusing the beams in a single crystal of BBO, high intensity broad-bandwidth femtosecond pulses are used to generate 50μJ of light at 270nm (up to 1% THG efficiency). It is proved that the major contribution to the THG observed is the third-order process, not the cascaded second-order process. And the primary reasons why THG efficiency is about 1% is that 1ωlight is frequency-chirp beams and BBO crystal isnt tuned to optimized angle. At last, the methods to improve the third harmonic conversion efficiency have been put forward.