GENERATION AND DETECTION OF WIDE-FREQUENCY-RANGE ACOUSTIC PHONONS BY IMPULSIVE STIMULATED BRILLOUIN-SCATTERING

The impulsive stimulated Brillouin scattering was applied over a wide frequency range. Using the light pulse of a non-mode-locked Q-switched YAG laser for probing, we could observe acoustic phonons with frequen cy as high as 5.41 GHz and as low as 46.1 MHz. Instead of scanning an optical delay line, the non-mode-locked Q-switched pulse was electroni cally scanned in the time domain. This gave the system an effective re ctangular pulse, allowing the pulse to be adjusted to a desired length and at the same time, enabling minimum heating of the sample. The the diffracted light was detected using an avalanche photodiode together with a digital oscilloscope in the low-frequency region and using a st reak optical oscilloscope in the high-frequency region.