Heterodyned self-mixing laser diode vibrometer

摘要

This patent describes a new method for remotely measuring vibration of an object based on laser Doppler vibrometry. The method combines an external two-pass frequency shifting technique with self- mixed, heterodyne detection to provide a compact measurement system that requires only three optical components. A standard diode laser package, consisting of a laser and a monitor photodiode, is used to emit light and detect the scattered signal, a lens is used to collimate the light, and an external modulator is used to shift the optical frequency. The diode laser may be used with or without temperature stabilization. The unique design permits the measurement of objects from a range of long distances without the need for focusing or alignment. Measurements made with the system are characterized by high signal-to-noise ratio, wide dynamic range, and simple alignment.