We present a study on the total internal reflection of nano-acoustic waves (NAWs) at the air∕GaN interface. The coherent NAW was generated and detected by piezoelectric InGaN∕GaN multiple quantum wells using a femtosecond transient transmission technique. With suitably designed sample structures, the fact that strain of the NAW experiences a sign change after total internal reflection at the air∕solid interface is examined directly. The surface roughness of the sample was found to distort the wave front of the NAW and to diminish the measured amplitude of the reflected NAW.

By generating coherent nano acoustic waves in InGaN/GaN multiple-quantum-wells and analyzing their echo signals from the sample-air interface, we studied the propagation and reflection properties of the THz acoustic strain waves in GaN

For the purpose of functional third harmonic optical microscopy, it is necessary to find a method to locally enhance third harmonic generation at specific cellular site. We have demonstrated that by matching the third harmonic generation frequency of a Cr:forsterite laser and the surface plasmon resonance frequency of <50-nm silver nanoparticles, localized enhancement of third harmonic intensity of more than 100-folds can be achieved both in phantom and in real biological tissues. This strongly enhanced third harmonic signal can then be applied to specific molecule imaging by attaching the nanoparticles to the target molecule with the advantages of noninvasiveness and deep penetration capability.