Heterodyne laser Doppler vibrometer using a Zeeman-stabilized He–Ne laser with a one-shot frequency to voltage converter

Abstract

The vibration measurement technique using a heterodyne laser interferometer is addressed in this article. A Zeeman-stabilized He–Ne laser is used as the light source. The frequency stabilization of the laser is performed by controlling the length of the laser tube via thermal control. The stability of the laser is measured by comparing it with an iodine-stabilized He–Ne laser. The root Allan variance of the laser is measured as below 5.5×10−9. The frequency modulation demodulation to convert the frequency of the interferent signal to the voltage signal using a one-shot frequency to voltage (F∕V) converter is also addressed. Simplicity and robustness of the measurement can be achieved by using the one-shot F∕V converter. Since the Doppler frequency is shifted by the heterodyne beat frequency, the compensation algorithm is added to remove the shifted frequency of the interferent signal in the signal processing circuit. The bandwidth of the signal processing circuit using the one-shot F∕V converter is 20kHz, and the maximum detectable velocity of the target is ±0.13m∕s. The proposed vibration measurement technique proved to be very fast and robust to external disturbances by experimental results.