Abstract
The effect of gas adjacent to the sample surface on the photo-acoustic displacement (PAD) measurement was studied by using an extremely sensitive laser interferometric probe with a sensitivity of 0.1 picometers. For silicon, the PAD signal measured at atmospheric pressure increased about 18% as compared to the signal obtained in vacuum, and varied by less than 0.7% for a change in pressure of 5% around 1 atm. It is shown, by a simple theoretical model, that the variation of the PAD is caused by a change in refractive index of the gas and the real PAD can be accurately obtained by correcting this effect.
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