MODULATORS :: APPLICATIONS :: Interferometry 

If the light in an interferometer is linearly polarized, a PEM may be used to modulate the interference at a high frequency (e.g. 50 kHz).

This technique may be used with many types of interferometers, but the technique will be demonstrated with a Mach-Zehnder interferometer, Figure 1.





The PEM retardation axis should be parallel to the direction of polarization. Addition of a PEM optical element in the other path of the interferometer will make the (average) optical path length in both legs of the interferometer the same. A detector with small area placed at the output of the interferometer will exhibit a modulated signal at the PEM operating frequency for a PEM peak retardation of ~/4.

Another application involves the use of the PEM with an FTIR setup to achieve “double modulation”. See, for example, the application note on Vibrational Circular Dichroism.