Based Chirp Reversal And Mosaic Raster Laser Pulse Efficient Compression Technique

Successful application of Chirped pulse amplification (CPA) technology in the field of laser had dramatically improved the output capacity (energy and power) of short-pulse laser facilities, which has been kept in a stagnant level for almost20years before. And this realized unprecedented extreme conditions, which provided impact and opportunities to materials science, plasma physics, laser fusion and other research fields.Large-scale CPA laser facilities usually work in a mode as "pulse being stretched in a positive dispersion stretcher-energy amplification-compressed in a negative dispersion compressor." The stretchers which provide positive dispersion often use large aperture lens or concave mirrors, which can’t be processed easily and be of high cost. In addition, aberration control and alignment accuracy requirements for these components are severe. If the requirements can not be met, it tends to distort the beam quality and decrease the final focused intensity. Therefore, it’s meaningful to simplify the structure of the stretcher to avoid or reduce the impact of the large-aperture components, to reduce costs, and to improve the output laser beam quality.In addition, the gratings for pulse-compression with limit size and limit damage threshold are bottleneck of the output capacity for a high-energy short-pulse laser facility. Expanding the grating’s aperture in a tiling manner to increase the output capacity is almost an inevitable choice. However, to ensure a tiled grating alternative to a single one, tiling errors must be controlled in a high precision, and environmental vibration may seriously distort the distribution of the focal spot. Real-time monitoring of tiling errors and stability control has always been a difficult problem, and some of the developed monitoring and control methods are very complex and expensive. So a simplified, practical and inexpensive error-control-method is important and valuable.An operation mode especially adaptable for CPA system with TGCs is proposed in this paper. The laser pulse is designed to sequentially pass through a parallel-grating compressor, which is essentially a stretcher with negative dispersion, parametric process for chirp reversal, energy amplification, and finally the compressor again to complete the CPA process (denoted as CRAC mode). That means we can use chirp reversal to simplify the structure of a stretcher, or even "remove" the independent stretcher. In addition, combination of chirp reversal and near-field inversion may improve the stability of the tiled gratings. Moreover, theoretical analysis showed that this CRAC operation mode will also be benefit to improve the band-pass of the overall system and to increase the utilization efficiency of the all amplified energy.The main contents in this paper are:(1) Chirped-pulse amplification system based on chirp reversal in optical parametric chirped-pulse amplification is proposed and experimentally demonstrated. The operation of this system can be described as "negative stretching-temporal chirp reversal-energy amplification-negative compression", named as CRAC mode, in which the pulse is stretched and compressed with the same gratings. Stand-alone stretcher adopting lenses or concave mirrors with large aperture can be omitted.(2) Calculation and analysis of chirped pulse transmitting in the amplifier chain is made. Simulation showed that with CRAC operation mode, the cut-off band-pass of the whole system can be increased and the spectral transmittance matching between stretcher and compressor can be better. Based on that, the SNR of the pulse and utilization ratio of the energy from amplifier chain can be improved.(3) Influence of the tiling errors from mosaic gratings used in a CPA system is analyzed. A group of "match relation equations" for the work laser and the monitor laser is proposed, which has been successfully used in a "two-pass tiled grating compressor". Experiment showed that, with wavelength and incident angle of the diagnostic beam being specially chosen, real-time monitoring and alignment can be achieved without disturbing the work beam. The far-field of the main laser beam and that of the diagnostic beam can vary in the same way with the tiling errors between the sub-aperture gratings. Rotational and translational errors can be controlled and compensated according to the far-field of the diagnostic beam.(4) A method,"combination of CRAC mode and near-field reversal", to diminish or remove the influence of tiling error and to improve the focused stability is proposed. Theoretical analysis shows that this method can increase the focused intensity to a great extent even if the piston error is not accurately controlled. So the monitoring scheme with this method can be simplified with improved stability.In general, some new ways and methods to solve the troublesome problems in a high-energy-short-pulse laser facility are proposed. A new operation mode--named as "CRAC" mode--is proposed and demonstrated for a CPA laser system. Methods for real-time monitoring and control of tiled-grating-compressor are also proposed and demonstrated.