The phase conjugation of the optically nonlinear stimulated Brillouin scattering (SBS) process using heavy-fluorocarbon materials effectively compensated thermal degradation at two amplifier lines, resulting in an output energy of 7.4 J at 50 Hz. When combining two beams, the beat wave generation caused by the temporal coherence between the two beams can be prevented because the two beams leave at intervals longer than the coherence length of the pulse. The use of different Brillouin frequencies of reflection from different SBS substances can also be effective in preventing the interference effect caused by the spatial coherence between the two beams.
[Show abstract][Hide abstract] ABSTRACT: In order to improve the measurement performance of incoherent Thomson scattering diagnostics, a high performance phase conjugate mirror based on stimulated Brillouin scattering (SBS-PCM) is applied to a Thomson scattering system for the first time in the JT-60U tokamak. We have demonstrated that a SBS-PCM which uses heavy-fluorocarbon liquid showed a high reflectivity of 95% at a high input-power of 145 W. Using the SBS-PCM, two newly developed methods were employed to increase the amount of scattered light. In the first method, we first developed a new optical design to provide a double-pass scattering scheme with the SBS-PCM. In this new optical design, a laser beam passing through the plasma is reflected by the SBS-PCM, and the reflected beam is returned via the same path by means of the phase conjugate effect, and is then passed through the plasma again, in order to increase the scattered light. A double-pass Thomson scattering scheme using the SBS-PCM was demonstrated in JT-60U ohmic plasma, resulting in an increase of the scattered light by a factor of 1.6, and the reduction of relative error by 2/3 for electron temperature measurement in contrast to single-pass scattering. A multi-pass Thomson scattering scheme is also proposed based on the results of double-pass scattering. It is estimated that multi-pass scattering allows the generation of several times the amount of scattered light, and the reduction of the relative error for electron temperature measurement by 37% in contrast to single-pass scattering. Regarding the second method, a high average-power of YAG laser system was developed by applying the SBS-PCM to a existent diagnostic laser. As a result, the average-power was increased by over 8 times in contrast to the average power of the original system, achieving up to 368 W (7.4 J × 50 Hz).
Journal of Plasma and Fusion Research 01/2004; 80(10):870-882. DOI:10.1585/jspf.80.870
[Show abstract][Hide abstract] ABSTRACT: Phase conjugation mirror with stimulated Brillouin scattering (SBS-PCM) is useful to compensate the wave-front distortion due to the thermally induced aberration and depolarization of average power solid-state lasers. SBS-PCM is reviewed as a promising approach for achieving power scaling of solid-state laser.
[Show abstract][Hide abstract] ABSTRACT: A liquid-cooled ceramic Nd:YAG split-disk laser amplifier has been designed for a high-average-power laser system. The maximum average output power of 17.1 W (1.71 J at 10 Hz) and the beam size of far-field pattern with 1.5 times diffraction limit was obtained. The combination of liquid cooling for disk laser material and wavefront compensation with a phase conjugation mirror was demonstrated. The wavefront degradation by liquid cooling was observed and measured with Michelson interferometer and far-field patterns. (c) 2006 Elsevier B.V. All rights reserved.
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