Posted in | Spectrometers

PMA 50: Polarization Modulation Measurements

The external accessory PMA 50 from Bruker has been developed exclusively for polarization modulation measurements. It can be adapted to Bruker TENSOR and VERTEX FTIR spectrometers. All electronic and optic components in the PMA 50 module are optimized for the polarization modulation.

It is possible to realize both circular dichroitic experiments such as VCD spectroscopy and linear dichroitic measurement methods like PM-IRRAS using this dedicated system.

The photoelastic modulator (PEM) forms the core of the polarization modulation technique, and has a nominal modulation frequency of 42 kHz. The sum and the difference signals can be gathered simultaneously with maximum sensitivity using the parallel 24-bit dual-channel data acquisition technology.

The PMA 50 module displays a short beam path, and provides optimal stability and S/N ratio.

In combination with the automated software controllable internal aperture and optical fibers in VERTEX and TENSOR spectrometers, the signal quality can be further optimized with respect to the desire sample size and spectral range. In order to reach the highest performance in polarization modulated applications, the polarized light is focused on the detector element by a lens providing that only non-polarizing optical parts are used after polarization.


The key applications of the PMA 50 are as follows:

  • Purity control of enantiomers
  • Corrosion processes
  • Investigation of (sub-) monolayers or further ultrathin coatings on metal surfaces with no need of reference
  • Elimination of water vapor absorption
  • Characterization of the secondary structure of peptides and proteins
  • Discrimination of conformation for enantiomers

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