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