Study On The Technology Of Laser Contrast Enhancement And Control Of Ultra-short Pulse

Ultra-short and ultra-intense laser has very short pulse duration and extremelyhigh peak power. Thus, it is very important to research the ultra-fast spectrum, thegeneration of X-ray source, higher harmonic and high field physics. However, the lowtemporal contrast of the ultra-short and ultra-intense laser seriously restricts itsapplication in high field physics. This paper around the temporal contrastenhancement of the ultra-short and ultra-intense lasers and the main works as follows:1. In this paper, we summarize research progress of the ultra-short and ultra-intenselasers at home and abroad. We introduce the research background of the temporalcontrast of the ultra-short and ultra-intense lasers and the methods of improvingthe temporal contrast. We also compare the advantage and disadvantage of thesemethods for improving the temporal contrast of the ultra-short and ultra-intenselasers.2. We propose a novel method to improve the temporal contrast. This method isbased on phase conjugate wave generation, which is produced by degenerate fourwave mixing (DFWM) process. A theoretical model for improving the temporalcontrast of the the ultra-short and ultra-intense lasers is established. Theoreticalsimulation indicates the impact of spectral bandwidth and the generated phaseconjugate wave conversion efficiency. The theoretical results show that thetemporal contrast can be enhanced to about the cube of the temporal contrast ofthe input pulse. The temporal contrast is improved by a wide margin because ofthe phase conjugate wave generation. The output pulse not only has high temporalcontrast, but also has no distortion in time domain and good beam quality.3. We research that the nonlinear elliptical polarization rotation (NER) is used toimprove the temporal contrast of the ultra-short and ultra-intense lasers. We alsoset up a theoretical model to assess the contrast enhancement based on thismethod. Theoretical simulation indicates the impact of spectral bandwidth and the conversion efficiency of the NER. The theory analysis and numerical study theeffects of the extinction ratio of polarizer pair, power density, included angle ofquarter wave-plate to the temporal contrast. The theoretical results show that thetemporal contrast can be improved by3orders. There is a optimum angle andoptimum power density to obtain high contrast and high conversion efficiency.4. Experimental investigations of temporal contrast enhancement based on phaseconjugate wave generation have been carried out with the optical parametricchirped pulse amplification (OPCPA) laser system. The output phase conjugatewave is measured by a commercial high dynamic third-order corss-correlator(Sequoia1000). The experimental results show the temporal contrast of pulseswas improved from1.7u103to8.6u108with the conversion efficiency of10%.5. We propose a new highly efficient scheme for temporal filters devoted toultra-short pulse contrast enhancement. The filter is based on nonlinear ellipserotation (NER) by using CS2. Experimental investigations of temporal contrastenhancement based on NER have been carried out with the KHz3TW Ti:sapphire laser amplification system. Experimental result shows that the totaltransmission efficiency of the scheme is high as30%.