Stimulated Brillouin scattering of chirped optical pulses

Abstract

Stimulated Brillouin scattering (SBS) has become well known for its ability to remove phase distortions imposed on a laser beam. However, to date, most SBS experiments have been performed using nanosecond laser pulses, so that the incident laser pulse duration exceeds the phonon lifetime of the SBS active medium. When the incident pulse is shorter in duration than the phonon lifetime, the SBS process becomes transient, and the gain is dramatically reduced. Therefore, higher input laser intensities are required to reach threshold. Very often, these intensities exceed those required to observe competing effects such as stimulated Raman scattering or optical breakdown. Cumulative SBS has been shown to reduce the SBS threshold for short optical pulses. In this technique, several pulses, separated by less than the phonon lifetime of the SBS medium, are used to excite SBS. In this way, the phonon field gradually grows from several incident pulses. Chirped pulse amplification has become a standard technique for obtaining high peak-power optical pulses. Therefore, it is desirable to develop a technique to generate efficient SBS using chirped optical pulses. In this study, we have shown that cumulative SBS can efficiently generate SBS using multiple, chirped optical pulses. Using N2 as a SBS active medium, we observed reflectivities exceeding 60% when the SBS process was excited using broadband, chirped laser pulses. The incident pulses were ~120 ps in duration and possessed a 1-nm bandwidth. We also observed that the SBS process preserves the linear chirp of the applied field and that the reflected pulse could be compressed to streak camera-limited resolution of 8 ps upon double passing a dispersive grating pair.