Laser heterodyne based stress measurement technology for optical elements

• A stress measurement method based on laser heterodyne technology for optical elements is proposed. • Three algorithms used to extract the phase accuracy of heterodyne signal are discussed. • The experimental results show that the phase measurement accuracy is better than 0.001 rad and the relative error is better than 0.01%. Common stress measurement methods of optical elements often suffering from complex process and limited aperture. To meet this challenge a new method based on laser heterodyne technology is proposed. In this method the stress measurement is transformed into the measurement of optical path difference induced by birefringence according to the stress birefringence effect, and the signal light is demodulated by laser heterodyne detection. This method has simple measurement process, and solves the problem of large-aperture measurement by combining with MEMS scanning technology. The basic structure of the measurement system is established, and its theoretical model is derived in detail. The experiment result of a fused silica sample with thickness of 2 mm reach an accuracy as high as 1.8 kPa, and the relative error is less than 0.01%.