Song Zhou

Progress on the XG-III high-intensity laser facility with three synchronized beams

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.

High-accuracy measurement and compensation of grating line-density error in a tiled-grating compressor

The grating tiling technology is one of the most effective means to increase the aperture of the gratings. The line-density error (LDE) between sub-gratings will degrade the performance of the tiling gratings, high accuracy measurement and compensation of the LDE are of significance to improve the output pulses characteristics of the tiled-grating compressor. In this paper, the influence of LDE on the output pulses of the tiled-grating compressor is quantitatively analyzed by means of numerical simulation, the output beams drift and output pulses broadening resulting from the LDE are presented. Based on the numerical results we propose a compensation method to reduce the degradations of the tiled grating compressor by applying angular tilt error and longitudinal piston error at the same time. Moreover, a monitoring system is setup to measure the LDE between sub-gratings accurately and the dispersion variation due to the LDE is also demonstrated based on spatial-spectral interference. In this way, we can realize high-accuracy measurement and compensation of the LDE, and this would provide an efficient way to guide the adjustment of the tiling gratings.

Design and optimization of the seed pulse generation scheme for precise beam synchronization in the Xingguang-III laser

Xingguang-III is a large hybrid optical parametric amplification/chirped pulse amplification laser that outputs synchronized femtosecond, picosecond, and nanosecond beams with three different wavelengths, i.e., 800, 1053, and 527 nm, respectively. We present here an in-house front-end system design that generates the 1053 nm seed laser for the ps/ns beam directly from the 800 nm femtosecond laser, which enables the three beams to have intrinsic synchronization. The results show that a seed laser of 140 μJ energy and 1053 nm central wavelength with 34 nm spectral width (FWHM) is generated and the shot-to-shot timing jitter (peak-to-valley) between the fs and the ps beam is less than 1.32 ps.

Novel front end design for synchronized output pulses with zero timing jitter in XG-III laser facility

XG-III laser facility is a petawatt laser which has a unique feature of three synchronized pulses output for various pump-probe experiments. To realize the synchronization with zero timing jitter, we have designed and implemented a novel front-end system based on super-continuum injected femtosecond optical parametric amplification (fs:OPA). Critical parameters of fs:OPA were optimized for the best conversion efficiency. Experimental results verified that major design specifications such as pulse energy, central wavelength and spectral width were fully accomplished and a high pulse contrast ratio was also achieved by the fs:OPA process.

Array element auto-tiling based on capacitive displacement sensor

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.

Spectral shaping of the amplified signal in optical parametric chirped pulse amplification

A spectral shaping method during the optical parametric chirped pulse amplification is presented. The relationship between the temporal shape of the signal pulse and the pump pulse is analyzed theoretically, which shows that the temporal shape of the signal pulse can be modulated through modulation of the pump pulse. This is proven by our verification experiment. And we have successfully used this method in the pre-amplifier of the XG-III laser facility to modulate the signal spectrum to match the requirements of the main amplifier.

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.