Generation of frequency-tunable nanoacoustic waves by optical coherent control.

We have developed a system to generate arbitrary wave-form nanoacoustic waves (NAWs) with a piezoelectric InGaN/GaN single-quantum well. Based on an optical coherent control technique, acoustic frequency tunability in the subterahertz range is realized within only one fixed sample. The acoustic generation mechanisms, especially the in-well piezoelectric field Coulomb screening which tends to be saturated at high carrier concentrations, are discussed with optical power dependency. With the generated NAWs propagating in the c axis of a GaN thin film, the lifetime of the 500 GHz longitudinal-acoustic phonon pulses in GaN is measured to be longer than 420 ps, corresponding to a GaN depth more than 3.3 μm. [ABSTRACT FROM AUTHOR]