A New Method of Photothermal Displacement Measurement by Laser Interferometric Probe -Its Mechanism and Applications to Evaluation of Lattice Damage in Semiconductors

A new, highly sensitive technique for measuring photothermal displacement using a laser heterodyne interferometric probe has been developed. This technique is based on the detection of phase changes in the probe beam and is very sensitive to the presence of lattice damage in semiconductors. It has been found that the phase change is caused by the thermal expansion of a sample surface induced by absorption of a modulated pump beam. The displacements of metals and semiconductors measured by this technique coincided with the results predicted by a thermal diffusion model. These displacements simply depended upon the ratio of the thermal expansion coefficient to the thermal conductlvity of a sample.