Stimulated Brillouin Scattering Cell Research Articles

The effect of pump beam focusing characteristics on stimulated Brillouin scattering

Parameters including pump energy, beam waist radius, length of gain medium and beam divergence all affect the generation threshold and output pulse characteristics of lasers that utilize the stimulated Brillouin scattering (SBS) effect. In this paper, we investigate the effect that changes to the pump beam focusing parameters (namely beam divergence and beam waist) have on the output characteristics of the Stokes beam generated through the SBS process. This study is conducted both theoretically and experimentally using a single-cell SBS structure. The results highlight that pump beams with a small divergence angle at the focal point within the SBS cell are favorable for the generation of Stokes beams with short pulse lengths. Here, we demonstrate the generation of a Stokes beam with a pulse width of 854 ps using a pump pulse with a pulse width of 7.2 ns, which was focused to a spot with a divergence angle of 2.48 mrad.

水下物体测量中受激布里渊散射过程的非线性光学特性

Nonlinear optical properties of stimulated Brillouin scattering (SBS) to signal detection in water are analyzed. With the threshold characteristics, SBS only occurs when the high power laser is focused in the SBS cell. When there is an object present in front of the focus, it leads to lower incident intensity and then SBS does not occur. The backward SBS signal depends on the focusing location. The nonlinear optical properties of SBS process in the focusing regime are analyzed theoretically. With the object coming near to the focusing center, the backward Stokes signal rises up from zero to a maximum, and then grows to saturation. The delay time of the echo signal to pump signal can give the object location. In experiment, the peak position of varying rate of energy can give object location.

A TRANSIENT, THREE-DIMENSIONAL MODEL OF STIMULATED BRILLOUIN SCATTERING

An efficient numerical 3-D model of transient stimulated Brillouin scattering (SBS) is reported. The model is used to examine the effects of transient phenomena on the efficiency of phase conjugation by SBS and the mode structure of the Stokes and pump pulse inside the SBS cell. The effect of parameters such as phonon lifetime, input pulse shape and input energy on the transient fidelity of SBS is investigated. A new transient phenomenon which causes SBS fidelity degradation at high focal intensity (short Rayleigh range) is examined.

Self-starting short-pulse XeCl laser with a stimulated Brillouin scattering mirror

A commercial XeCl laser system is operated with a phase-conjugating mirror based on stimulated Brillouin scattering (SBS). No conventional start resonator is required. The near-field profile is converted from rectangular to near-Gaussian and the far-field spatial beam quality is increased by up to 60% relative to a conventional plane-plane resonator. The small reflectivity of a single SBS cell reduces the laser output power. A double-cell arrangement improves the reflectivity and the laser power, resulting in a simple excimer SBS resonator with improved brightness.

Pulse lengthening by intracavity stimulated Brillouin scattering in a Q-switched, phase-conjugated Nd:YAG laser oscillator

The usual solid-state laser systems with phase-conjugating elements produce Q-switch pulses of some 10 ns pulse width, which for many applications is too short. In the following study an additive stimulated Brillouin scattering (SBS) cell is introduced in the cavity to compensate for this Q-switch behavior by nonlinearly increasing intracavity losses resulting from the direct output coupling of the Stokes wave generated in this additive cell. For direct output coupling this study takes advantage of polarizing optical elements in the laser cavity. With this arrangement an averaged pulse duration of approximately 300 ns is realized compared with the 60-ns pulse duration that is realized when working without an additional SBS cell. The experimental results are compared with numerical calculations based on modified rate equations for the active medium and a two-wave-mixing formalism for the nonlinear interaction with the SBS media.

The effect of pump bandwidth, lens focal length and lens focal point location on Stimulated Brillouin Scattering threshold and reflectivity

The dependence of the Stimulated Brillouin Scattering (SBS) threshold on the focal length of the lens has been measured for two extreme limits of the pump bandwidth. For a single mode pump with a long coherence length the threshold is found to be independent of the focal length while for a broadband pump the threshold is found to vary quadratically with the focal length. The measurements also show that the location of the focal point in the SBS cell can seriously affect the reflectivity when the pump energy is small.

Beam combination by stimulated Brillouin scattering

Phase conjugation of two beams by stimulated Brillouin scattering (SBS) was studied with a computer model and investigated experimentally. The relative phase of the return beams was found to vary randomly if the pump beams were well separated in the SBS cell but remained fixed and equal to the inverse of the pump relative phase if the beams overlapped. Backward Stokes injection was used to lower the threshold and increase the reflectivity of SBS.