Angular bandwidth for Brillouin amplification

The angular bandwidth (ABW) of a Brillouin amplifier is shown to be dependent on the spectral bandwidth of the interacting beams in a counterpropagating geometry. Theory and experiment reveal that the actual ABW for typical lasers is much larger than monochromatic theory suggests. For single-longitudinal-mode pulses of a 8.5-ns duration interacting in CS₂ the ABW is equal to ±320 mrad (±180°), corresponding to an external angle of ±29°. However, to permit us to take advantage of the full ABW afforded by the Brillouin interaction, proper design of the amplifier is necessary to ensure that angular walk-off loss does not occur.