Measurement Of Standing Wave Induced SBS Phase Jitter By Using Optical Beat Frequency

In recent years, laser Inertial Confinement Fusion(ICF) has been focused intensely by the public due to its key role in the field of energy and national defense. This new type of ignition method needs megajoule level of laser pulse energy and 5 Hz to 10 Hz repetition frequency, which largely increases the difficulty of cooling the gain medium and limits the development of large diameter laser driver. A method to achieve ICF is to use Stimulated Brillouin Scattering(SBS) to combine each beam. This paper proposes to use time beat frequency to measure the stability of the phase to solve the problem of measurement errors induced by poor beam quality.This paper is based on deducing three waves coupling physical process of SBS interaction, i.e., Navier Stokes equation of acoustic wave field and Maxwell’s equations coupled by electrostriction effect, to establish physical model of SBS interaction. After discretizing the model, coherent standing wave factor is added, physical model of density modulation is established and finite difference method is used to process the model.Theoretically, time beat frequency measurement is superior to the space coherent measurement in terms of phase stability of stimulated brillouin scattering is demonstrated when beam quality is poor. After characterizing the mixed medium frequency shift, C6H6 and CCl4 are selected for the experiment, and Brillouin frequency shift is calculated and measured with the two kinds of medium under the condition of the different mixing ratio.In the experiment, optical beat frequency is used to measurt the the phase jitter of SBS, and the experiment setup is modified and redesigned compar ed to the original one. The wavelength of the pump is 532 nm, the frequency shift of different mixing ratio of SBS medium was measured and analyzed by redesigning the experiment setup. The result that stability of coherent standing wave of SBS phase is higher than that of SBS with common structure is required by changing the power of incident light wave. When beam quality is poor, time beat frequency measurement is superior to the space coherent measurement in terms of phase stability of SBS is proved by changing the energy ratio of the two beams and pore diameter.