Laser fusion requires very high energy0power output with high repetition rate over 10 Hz, which is very difficult with the current laser technologies. However, the recent research work on the phase controlling of the stimulated Brillouin scattering wave enables the realization of this kind of laser fusion driver. The recent progress of controlling the phase has been successfully demonstrated by the self-generated density modulation method proposed by one of the authors Kong!. Nevertheless, it showed a long-term fluctuation of the phase because of the long-term fluctuation of the density of the SBS medium due to the thermal fluctuation. This long-term thermal fluctuation is inevitable a fact in nature. The authors used a specially designed stabilizing system for the phase controlling system, which has the PZT control of the mirror for phase controlling SBS-PCM~the so-called feedback mirror!. This system stabilizes the phase controlling system very well for more than 1 h. This technique will help the laser fusion driver to be realized sooner than expected. In addition, we propose a similar scheme to be applied to the ultra-fast pulse laser system, which must operate at high repetition rate for the laser fusion energy power plant.

A new concept of laser fusion driver is proposed, which uses a beam combination technique with stimulated Brillouin scattering phase conjugate mirror (SBS-PCM). It is constructed systematically with a cross-type amplifier as a basic unit. In the first part of this paper, we introduce the cross-type laser amplifier using SBS-PCM, with several advantages by experimental results. These advantages are the ideal properties for practical laser fusion driver, such as the perfect isolation of leak beam, the compensation of thermally induced birefringence through the amplifiers, the easy maintenance and alignment insensitiveness, and the freely-scale-up energy. Next, some successful results for the phase control of SBS-PCM are presented, which is one of the main problems in the current beam combination laser using SBS-PCM. Particularly, a new technique for controlling the phase of SBS-PCM, “self-density modulation,” is introduced, which is the simplest ever among those reported. With the advantages of the cross-type amplifier using SBS-PCM and the novel method for controlling the phase of SBS-PCM, the proposed beam combination laser system is presented as the most promising one, which can contribute to the realization of high energy laser that can operate with high repetition rate over 10 Hz, even in the case of huge output energy over MJ.

An overview on current trends in stimulated Brillouin scattering and optical phase conjugation is given. This report is based on the results of the "Second International Workshop on stimulated Brillouin scattering and phase conjugation" held in Potsdam/Germany in September 2007. The properties of stimulated Brillouin scattering are presented for the compensation of phase distortions in combination with novel laser technology like ceramics materials but also for e.g., phase stabilization, beam combination, and slow light. Photorefractive nonlinear mirrors and resonant refractive index gratings are addressed as phase conjugating mirrors in addition.

A simple, compact, and efficient diode-side-pumped linear intracavity frequency doubled Nd:YAG rod laser with 50 ns pulse width and 124 W green output power Rev. Sci. Instrum. 81, 073104 (2010); 10.1063/1.3457000 Phase stabilization of a wave-front dividing four-beam combined amplifier with stimulated Brillouin scattering phase conjugate mirrors Appl. Phys. Lett. 96, 131116 (2010); 10.1063/1.3373629 Mode-locking optimization with a real-time feedback system in a Nd:yttrium lithium fluoride laser cavity Rev. Sci. Instrum. 78, 013105 (2007);

We have found that it is possible to preserve the temporal waveform of the reflected wave generated from stimulated Brillouin scattering (SBS) by using a prepulse technique. The waveform of the SBS wave usually shows a steep rising edge in the ordinary SBS process. It has been found that the waveform of the reflected wave depends on both the prepulse energy and the time delay between the main pulse and the prepulses. A prepulse energy of 5 mJ and a time delay of 5 ns have been measured to be the optimum values under the experimental conditions. This prepulse method is useful in developing a multistage system employing several SBS cells in series for high-power laser applications.