Noncontact measurement of elasticity using optical fiber-based heterodyne interferometer and laser ultrasonics

Abstract

We propose the noncontact measurement of elasticity by using an optical fiber heterodyne interferometer and laser ultrasonics. The surface acoustic wave (SAW), that is generated by the laser pulse irradiation on the sample surface and propagating along the surface, is optically monitored by the heterodyne interferometer without taking any contact with the sample. By taking several measurements with changing the relative distance between the excitation and the measurement points, the phase velocity of SAW was calculated and from which the elasticity of the sample could be obtained. This proposed method was experimentally evaluated by using PDMS samples having various mixing ratio of curing agent and PDMS. For the sample of a 12:1 mixing ratio, the phase velocity was measured as about 39.46 m/s and the Young's modulus as about 1987 kPa. This technique is expected to detect the mechanical properties of biological tissues also.