Displacement sensitivity comparison between the first two symmetrical in-plane modes of a tuning fork crystal oscillator by using an optical chopping method

We compared the displacement sensitivity between the first two symmetrical flexural resonant modes of a tuning fork crystal oscillator. An optical chopping method was employed to detect the vibrational modes of the tuning fork. Displacement sensitivities for the first two modes were extracted by applying a sinusoidal excitation voltage to the tuning fork crystal oscillator and detecting the oscillating amplitude of the focused laser beam chopped by the vibrating tine of the oscillator. We found that the ratio of the second mode sensitivity to the first one was 0.0113, in reasonable agreement with the theoretical value of 0.0131.