LASER VIBROMETER BASED ON OPTICAL-FEEDBACK-INDUCED FREQUENCY-MODULATION OF A SINGLE-MODE LASER-DIODE

We describe a sensitive and inexpensive vibrometer based on optical fe edback by diffuse scattering to a single-mode diode laser. Fluctuation s in the diode laser's operating frequency that are due to scattered l ight from a vibrating surface are used to detect the amplitude and fre quency of surface vibrations. An additional physical vibration of the laser provides an absolute amplitude calibration. The fundamental band width is determined by the laser response time of roughly 10(-9) s. A noise floor of 0.23 nm/Hz(1/2) at 30 kHz with 5 x 10(-5) of the incide nt light returning is demonstrated. This instrument provides an inexpe nsive and sensitive method of noncontact measurement in solid material s with low or uneven reflectivity. It can be used as a vibration or ve locity sensor.