  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.
