Stimulated Brillouin scattering (SBS) dye laser amplifiers

In optically pumped dye laser amplifiers, pump energy is necessarily lost to the gain medium. With collimated beams the pumping intensity therefore decreases as it propagates, so that the pumping rate varies throughout the gain volume. Because of this, the pumping rate is generally only optimum at a given point within the amplifier. However, this condition changes if a focusing lens is placed immediately in front of a longitudinally pumped dye cell, so that there is a significant geometrical reduction in beam diameters within the gain volume. Although pump energy will continue to diminish, the pump intensity can be preserved. The pumping rate can therefore be similar throughout the gain volume. An additional benefit is that since the signal also passes through the same lens, the signal intensity is geometrically increased in addition to the gain in intensity experienced through normal laser amplification. This enhancement in signal intensity leads to a more efficient energy extraction and further contributes to a higher overall gain. This paper considers the extreme case where the beams are fully focused within the gain medium. Here, the signal is double-passed through the gain volume by phase conjugation through SBS. An SBS dye amplifier combines high gain with excellent beam quality, high conversion efficiency and extremely low levels of amplified spontaneous emission (ASE), in a simple compact design.