Comparison between different types of feedback SBS mirrors used in solid state lasers

Abstract

ABSTRACT An effect of a SBS feedback mirror started by initial laser radiation is analyzed for loop and ring SBS-mirror schemes. Ithas been shown experimentally that the laser output power can be increased considerably by using both feedback schemesfor stimulated scattering excitation as compared to SBS mirror without feedback. The observed distinctions in the action oftwo lasers with these schemes are explained by different nonlinear mechanisms of SBS-ainplification in these cases.Key words: stimulated Brillouin scattering,(SBS) , feedback, solid-state laser, SBS-mirror.1. INTRODUCTIONEXternal SBS-mirrors started up by radiation of an initiai laser strongly influence the generation dynamics and outputradiation. This influence manifests itself mainly in two aspects: power and spatial characteristics of output radiation. First,including the SBS-mirror into a laser resonator during the laser action, leads to an additional increase in Q and a growth inthe power efficiency. Second, since the wave front of scattered radiation is phase conjugative with respect to the pump front,radiation phase distortions in the cavity are compensated and, the quality of the output radiaton remains the same as that ofinitial radiation. However, high laser radiation intensities are required for the SBS-mirror excitation. This leads to anundesirable competition with another nonlinear optical processes and heating of the nonlinear medium, in particular, in thecase of the pulse repetition regime. Moreover, the larger the excess in intensity over threshold the higher the SBS-mirrorefficiency. Hence, the reduction of the stimulated scattering threshold is very desirable for the effective operation of theSBS-mirror.The substantial reduction of the SBS-nurror excitation threshold can be achieved when optical feedback is applied. Atpresent, the loop and ring feedback schemes are the best-studied cases'3. These studies have demonstrated that the requiredpower decreases appreciably and the phase conjugation quality becomes higher when the feedback scheme is used for SBSexcitation. However, in spite of their obvious advantages, the SBS-mirrors with optical feedback have first been applied in