Round-trip Phase Shift Research Articles

Asymmetric Mode of an Off-axis Diaphragmed Laser

Abstract Diaphragmed resonators have been widely studied in the axially symmetric case. Here we present some experimental and theoretical results concerning the field distribution of an off-axis apertured laser. Measurements have been made with a commercial Argon laser based on a plano-concave cavity and operating at 488 nm. Calculations have been carried out using and extending a method presented previously for a symmetric resonator. Numerical results are given for the field distributions inside and outside the laser, the round-trip loss for the amplitude and the round-trip phase shift for various transverse misadjustments of the aperture. We find the asymmetric field distribution of the fundamental mode in both experimental and theoretical aspects.

Feedback effects on stimulated backscattering from laser-produced plasmas

Brillouin and Raman backscattering can be enhanced by reflective feedback from underdense plasma structures, such as quarter-critical density profile steepening due to two-plasmon decay. Rapid time modulation of broadband scatter can be explained by modulation of the feedback from a variation of the round trip phase shift due either to motion of the feedback surface, in Brillouin backscattering, or by periodic creation and destruction of the feedback surface itself, as in Raman backscattering.

Feedback-induced absolute instability of stimulated Brillouin scatter in bounded plasmas

A feedback mechanism is studied wherein Brillouin-scattered light from a finite plasma is reflected back inward from a sub-critical density shelf boundary. Sufficient feedback induces temporal growth in spite of possibly supersonic plasma flow and wave damping. The round trip phase shift of the feedback due to finite plasma length determines whether temporal growth is accompanied by frequency shifts. This feedback mechanism can explain experimental observations of rapid variation in the amplitude and frequency of Brillouin backscatter.