Measurement of photothermal vibrational displacement by a focusing error sensor

A focusing error sensor has been applied to the detection of photothermal vibrational displacements for the first time and the usefulness of this detection method has been confirmed. The principle of this sensor is based upon the steep reflectivity change near the critical angle in internal reflection. The signal amplitude of the focusing error sensor has been calibrated by interferometry, and the smallest detectable amplitude has proven to be of the order of picometer by the lock-in detection. Photothermal vibrational displacements of metal plates, plastics, and others have been measured against the excitation power and frequency. A subsurface structure of a stainless steel plate has been detected by one-dimensional scanning.

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