Use of detectors with photoelastic modulators

Photoelastic modulators (PEMs) are polarization modulation devices used in a wide range of experiments to probe the interaction between polarized light and matter. Experimental setups using PEMs rely on common detector types (photodiodes, photomultipliers, etc.) but care must be taken with their use. Specifically, 1. Care must be exercised to ensure proper impedance matching between the detector and the signal analyzing electronics, for example by using a trans-impedance preamplifier. 2. For silicon detectors, the responsivity at PEM frequencies (e.g. 100 kHz) decreases markedly for light wavelengths above 800-900 nm. 3. For circular dichroism experiments in the UV and visible, care must be taken in selecting a photomultiplier tube to minimize signal "artifacts" due to birefringence in optical components such as the sample cell and the PEM optical element.