Photoelastic Modulators (PEMs)

A Photoelastic Modulator (PEM) is an optical device that modulates the polarisation of light to gain information about mechanical stresses in materials. This is achieved by using photoelastic material that changes its optical properties due to mechanical stress. The PEM by Hinds Instruments utilises this effect to provide precise information about the stress distribution in an examined object.

The basic operating principle of the PEM is based on the photoelastic effect. A mechanically stressed sample exhibits birefringence proportional to the strain caused by the induced stress. Therefore, the PEM can be considered a birefringence modulator. The optics’ resonance results in birefringence along an axis that is either compressed or stretched, causing the light to travel faster or slower along this axis. For instance, in quartz glass, the light moves faster along the horizontal component when compressed and slower along the horizontal axis (parallel to the modulation) when stretched.

PEMs have several unique features, including a broad spectral range, large aperture, wide acceptance angle, and precise phase modulation. They are typically used for fast and highly sensitive measurements. Unlike Pockels cells and electro-optical modulators, optical elements made of quartz glass are isotropic when no stress is applied. This gives the PEM an expanded acceptance angle.

Hinds produces over a dozen standard PEM models that collectively cover the range from 130 nm to 57 µm.

Integrating Hinds Instruments’ PEM into existing measurement systems is generally straightforward. The modulator can be incorporated into optical setups and works well with common light sources and detectors. Hinds Instruments often provides software and interfaces that facilitate seamless integration into various measurement systems. This ensures easy adaptation to the specific requirements of the users.