Abstract
We report what we believe to be the first observation of coherent surface optical phonons generated by impulsive stimulation and detected by time-resolving second-harmonic generation (SHG). Several groups have reported the observation of coherent bulk phonons in various media by using short optical pulses to impulsively excite the vibrational mode.1 In contrast to linear reflectivity, SHG in reflection geometry is known to have decided surface sensitivity.2 Therefore, the observation of coherent surface phonons by using time- resolved SHG is possible. Indeed, we observe an oscillation in time-resolved SHG at 8.36 THz from GaAs (100) excited with 30-fs, 855-nm pump pulses. Because this oscillation frequency is in the forbidden gap for the bulk LO-phonon -plasmon coupling mode and is in good agreement with the oscillation frequency of the Fuchs-Kliewer surface phonon of GaAs,3 we assign it to the surface optical phonon.
© 1995 Optical Society of America
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