Modes of PEM Operation
PEM MODES OF OPERATION
The PEM may be used in either of two basic modes: as a modulator, to produce polarization modulation of a light beam, or as an analyzer, to determine the polarization state of a light beam.
USE AS A MODULATOR –
The PEM may be used to modulate a beam of light. One frequently used condition of operation occurs when the peak retardation corresponds to a quarter of the wavelength of the light being used.
Incoming light is linearly polarized in a plane which is at 45° with the long axis of the modulator. The result is light which oscillates between left and right circularly polarized light, with elliptically polarized light between these extremes. The optical oscillation frequency is at the modulator frequency (1f). This experimental setup is used for studies of circular dichroism.
USE AS AN ANALYZER –
The PEM may also be used to analyze the state of a polarized beam of light. A net circular polarization component will produce an electrical signal in the detector at the modulator frequency (1f). A net linear polarization component at 45° with respect to the modulator axis will produce an electrical signal in the detector at twice the modulator frequency (2f). Use of the reference signals from the PEM controller with lock-in amplifiers enables the simultaneous measurement of these two polarization components.
Used as a polarimeter, the PEM is capable of detecting polarization components weaker than 1 part in 106 of the total intensity. For complete details on use of the PEM as a polarimeter, consult the Stokes Polarimetry Application Note. PEM photoelastic modulators (PEMs) manufactured by Hinds Instruments, Inc. utilize both the photoelastic effect and the piezoelectric effect to produce an instrument generating modulation between different states of light polarization.
Hinds PEMs have a number of unique features that make them the key component in a variety of polarization modulation-based instruments. On this page, we provide a summary of these features.
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