Force to frequency conversion by intracavity photoelastic modulation

Force to frequency conversion (FFC) using the photoelastic effect inside a laser cavity is described. Analytic expressions are derived for scale factor, measurement errors, and laser dependent nonlinearity of appropriate instrument transducers. The influence of the laser pushing and pulling effects on linearity is calculated on the basis of the third-order saturation model. Our experiments with a modular test setup (633 nm) demonstrate FFC to be proportional to a high degree over almost 6 decades of input signal range. From 2 x 10(-4) up to 80 N we observed the noise equivalent resolution of 10(-4) N. The frequency response of our test setup was established from dc up to some kilohertz. FFC measurement range and resolution can be extended to 10(-6) N or smaller values by applying improved laser stabilization and miniaturizing the cavity length and size of photoelastic material.