Photo-elastic modulators enable high sensitivity polarimetry via the high frequency (f~50 kHz) modulation of the light polarization. The operation of the PEM is based on the photoelastic effect. In more detail: a piezoelectric actuator induces birefringence in an isotropic crystal by uniaxial strain, therefore, the velocity of the light is different for the polarization parallel and perpendicular to the optical axis. The phase shift occurred between the two orthogonal polarization can be modulated by changing the strain via an oscillating electric field.
Our laboratory has a fused silica (FS) and a ZnSe (ZS) PEM to cover the NIR-UV and the infrared photon energy regions, respectively.