High-power Laser Drive Broadband Third Harmonic Conversion Study

The instability of the laser and plasma interaction should be suppression by the introduction of temporal and spatial incoherence over the face of the beam, using techniques such as induced spatial incoherence (ISI) or smoothing by spectral dispersion (SSD), the rate at which the speckle pattern is smoothed is proportional to the bandwidth of the laser. The most effective method of temporal incoherence is to increase the bandwidth of laser. It should develop laser with bandwidth of 0.3～0.5nm to improve the uniform irradiation of the focal spot and near field pattern. At the same time, the large bandwidth can be useful to extract the energy of amplifier and suppression the stimulated brillouin scattering in the large aperture optics components, but the large bandwidth of fundamental frequency can reduce the efficiency of third harmonic generation. The high efficiency third harmonic generation of large bandwidth has been a hot spot in the harmonic conversion of high power laser system at home and abroad.In comparison with the several methods of broad bandwidth third harmonic generation, the Dual-Tripler Scheme is the most suitable to the high power laser system as so far. The work principle and the design procedure of it have been researched in this paper. This paper contains several parts as follows:1. The third harmonic generation of the temporal phase modulation pulse has been researched with a split-step algorithm base on fast Fourier transform and a Runge-Kutta integrator. The temporal phase modulation of pulse leads to the temporal modulation of intensity of the third harmonic and the conversion efficiency will decrease dramatically with the temporal phase modulation at the high intensity.2. Several methods of third harmonic generation with broad bandwidth and their merits and demerits have been study in this paper. Many more attention was paid to the Dual-Tripler Scheme. The results of numerical calculation about this scheme agree with the information in the literature from abroad. It laid the foundation of the design optimization about this scheme in the future.3. A Dual-Tripler Scheme was designed and it work principle has been checked by the chirp pulse laser.