Control of Coherent Acoustic Phonons
  Using sub-picosecond optical pump-probe techniques, coherent zone-folded longitudinal acoustic phonons (ZFLAPs) were generated and controlled in an InGaN multiple quantum well structure. A one-pump, one-probe differential transmission technique revealed that carriers injected near the barrier band edge were quickly captured into the quantum wells and generated strong coherent ZFLAP oscillations. Two-pump differential transmission was used to generate and control coherent ZFLAP oscillations through the relative timing and amplitude of the two pump pulses. Enhancement and suppression of ZFLAP oscillations were demonstrated, including complete cancellation of generated acoustic phonons for the first time in any material system. Coherent control was used to demonstrate that ZFLAPs are generated differently in InGaN multiple quantum wells than in GaAs/AlAs superlattices. 
Umit Ozgur, Chang-Won Lee, and Henry O. Everitt