Abstract:
A transient holographic pattern, which is called a transient reflecting grating (TRG), is produced on a solid surface when two pulsed lights are simultaneously irradiated at the same spot of a small size. By using a probe light delayed relative to the above excitation pulses, a time profile of the TRG is observed by changing the delay time of the probe pulse. The signal waveform includes information about generation and relaxation of ultrasonics and heat. Using this technique, a few-GHz ultrasonics were observed for a wide variation of material surfaces [A. Harata et al., Trends Anal. Chem. 14, 504--511 (1995)]. In this report highly sensitive detection of the TRGs utilizing surface plasmon resonance (SPR) is described. Energy deposition efficiency from light into heat was very effective under an SPR condition and the energy absorbed by a surface plasmon polariton (SPP) is concentrated on the solid surface. Utilizing an arrangement of total internal reflection for the SPP excitation, a TRG method about ten times more sensitive could be realized. A new type of SPR-enhanced TRG method is also proposed where the probe beam excites SPPs. The method made it possible to separate ultrasonics and the heat contribution to the TRG signal.