Robust Optical Detection Method for the Vibrational Mode of a Tuning Fork Crystal Oscillator

Abstract

We present an optical detection method for the fundamental vibrational mode of a tuning fork crystal oscillator in air. A focused He/Ne laser beam is directed onto the edge of one vibrating tine of the tuning fork; its vibrating motion chops the incoming laser beamand modulates the intensity. The beam with modulated intensity is then detected and converted to an electrical signal by a high-speedphoto-detector. This electrical signal is a sinusoid at the resonant frequency of the tuning fork vibration, which is 32.76 kHz. Our schemeis robust enough that the sinusoidal signal is detectable at up to 40o of rotation of the tuning fork.