Jingqin Su

Status of the SG-III solid-state laser facility

SG-III laser facility beam begins with a nanojoule energy laser pulse from the master oscillator and a fiber front-end system that can provide a variety of pulse shapes suitable for a wide range of experiments. The chirped pulse stacking method is used in the front-end system to generate arbitrarily shaped pulse with a rise time less than 50ps. The system stacks a set of 100-ps chirped pulses in fiber time-delay lines to obtain a 5-ns flat-top pulse with a spectral bandwidth of 1.2nm. The pulse is then transported to preamplifier modules under the middle of CSF for amplification and beam shaping. There is a total of 48 preamplifier modules on SG-III, each feeding a single laser beams. The main amplifier column of 4 high by 2 wide has been chosen as a module and the clear optical aperture is 40cm × 40cm. Small PEPC are chosen for system isolation and beam can be rotated by 90 degree in U-turn beam reverser located in the middle of TSF. After main amplifier, beams are subsequently redirected to final optics assembly in switchyard and are focused on the center of the target chamber with the diameter of 6m.

Preliminary experimental results of Shenguang III Technical Integration Experiment Line

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.

Production of Single Pulse by Landau Damping for Backward Raman Amplification in Plasma

The effect of plasma wavebreaking has been proposed to obtain single-pulse output for backward Raman amplification in plasma. However, some experiments indicate that the scheme may not be effective. In this paper, we propose the effect of Landau damping for this purpose. According to the theoretical analysis, the single pulse is generated by setting a proper plasma temperature to fully Landau damp the secondary spikes. Although the main pulse will also be partly suppressed by the damping, the effective efficiency can be enhanced. Moreover, the scheme is numerically demonstrated feasible by using the parameters of Princeton experiment [1], [2]. Additionally, the temperature to produce single-pulse output can keep below the critical temperature at various ratios of the plasma frequency to the pump pulse frequency.

Improved uniform irradiation by combining periodic chirped pulse, sinusoidal phase modulation light and lens array

A new method is proposed for obtaining two-dimensional beam smoothing. The periodic chirped pulse generated at the front end of the laser driver is dispersed in one direction and the bulk frequency modulation is used to generate another broad band. Then the beam is dispersed in the other direction. The pattern of the far-field is simulated. The result shows this method can reduce the high influence of the four outer corners. By combining a lens array, an improved uniform pattern on the target can be obtained.

Single laser pulse compression via strongly coupled stimulated Brillouin scattering in plasma

Laser amplification in plasma, including stimulated Raman scattering amplification and strongly coupled stimulated Brillouin scattering (sc-SBS) amplification, is very promising to generate ultrahigh-power and ultrashort laser pulses. But both are quite complex in experiments: at least three different laser pulses must be prepared; temporal delay and spatial overlap of these three pulses are difficult. We propose a single pulse compression scheme based on sc-SBS in plasma. Only one moderately long laser is applied, the front part of which ionizes the gas to produced plasma, and gets reflected by a plasma mirror at the end of the gas channel. The reflected front quickly depletes the remaining part of the laser by sc-SBS in the self-similar regime. The output laser is much stronger and shorter. This scheme is at first considered theoretically, then validated by using 1D PIC simulations.

Analysis of the synchronization error measurement via non-collinear cross-correlation

The method for measuring synchronization error of ultra-short pulses was introduced based on the principle of non-collinear cross-correlation. The analytical expression for the measurement was deduced according to the cross-correlation signal. The influences of angular error on the measurement were analyzed by simulated experiments. The incident angle and the angular error tolerance were both required to be considered and determined for the synchronization error measurement of ultra-short pulses. The results provide a theoretical basis for the measurement and control of the synchronization error in the coherent beam combination, plasma parameter diagnosis, etc.

Amplifying modeling for broad bandwidth pulse in Nd:glass based on hybrid-broaden mechanism

In this paper, the cross relaxation time is proposed to combine the homogeneous and inhomogeneous broaden mechanism for broad bandwidth pulse amplification model. The corresponding velocity equation, which can describe the response of inverse population on upper and low energy level of gain media to different frequency of pulse, is also put forward. The gain saturation and energy relaxation effect are also included in the velocity equation. Code named CPAP has been developed to simulate the amplifying process of broad bandwidth pulse in multi-pass laser system. The amplifying capability of multi-pass laser system is evaluated and gain narrowing and temporal shape distortion are also investigated when bandwidth of pulse and cross relaxation time of gain media are different. Results can benefit the design of high-energy PW laser system in LFRC, CAEP.

Two-pass full-tiled grating compressor with real-time monitoring and control for XG-III petawatt-class laser facility

A two-pass, full-tiled grating compressor with a unique feedback control system for precise alignment was realized in an XG-III petawatt-class laser facility, based on the chirped-pulse amplification (CPA) technique. Far-field images of both 0th order and −1st order diffraction light of a tiled grating assembly (TGA) were recorded using a CCD camera, by which the tiling errors of the TGA can be identified and corrected in real-time without disturbing the main beam. A final compressed pulse of 615 fs (FWHM) with a focal spot about 1.1 times the diffraction limited (DL) size was achieved.

Development of a sub-petawatt ultrashort laser facility

The paper presents the development of a sub-petawatt ultrashort laser facility, i.e. the upgraded super intense laser for experiment on the extremes (SILEX-I). The facility is a multi-stage Ti:sapphire chirped pulse amplification (CPA) laser system. Cross-polarized wave generation was used to improve the temporal contrast. An adaptive optical system was utilized to correct wavefront aberrations and to improve focusability before each shot. After upgrading, the maximum energy is 20.1 J, the recompressed pulse width is 26.8 fs and the peak power is up to 750 TW. The temporal contrast is around 109. The on-target focal spot size (full width at half maximum (FWHM)) is Φ6.5 μm and the focused intensity is greater than 4x1020 W/cm2.

Temporal pulse cleaning by a self-diffraction process for ultrashort laser pulses

Applying the self-diffraction process to clean ultrashort laser pulses temporally is a recently developed effective way to temporal contrast enhancement. In this paper, we attempt to clean ultrashort laser pulses temporally by the self-diffraction process. Experiments were carried out to study the temporal contrast improvement in the front-end system of an ultraintense and ultrashort laser facility, i.e. the super intense laser for experiment on the extremes (SILEX-I). The results show that the maximum conversion efficiency of the first-order self-diffraction (SD1) pulse is 11%. The temporal contrast of the SD1 signal is improved by two orders of magnitude, i.e. to 103, for a 2.4-ns prepulse with initial contrast of ~10. For a 5.5 -ns prepulse with initial contrast of 2×103, the temporal contrast of the SD1 signal is improved by more than three orders of magnitude.