Observation of the transient expansion of heated surfaces by picosecond photothermal deflection spectroscopy

The observation of the picosecond thermal expansion of an absorbing surface after a short heating pulse is reported for the first time to my knowledge. The measurement was performed on Si by adapting the method of photothermal deflection to a pump-probe technique using 1-psec laser pulses. This was achieved by separating out a novel deflection effect due to the gradient in the near-surface optical constants. The results are compared to a thermo-elastic model, and good agreement is found.