Dual PEM Systems
Dual PEM systems provide the capability to make real time polarization analysis measurements. When only one PEM is used, two measurements must be made with the sample rotated 45° after the first measurement. However, measurements can be made in real time using two PEMs mounted at 45° with respect to each other.
Hinds Instruments has four standard dual PEM choices for applications that require different useful apertures and measurements in different spectral regions. The dual PEM models are:
|Quarter Wave||Half Wave|
|I/FS50-60||Fused Silica||170 nm – 2 μm||170 nm – 1 μm||16 mm|
|II/FS20-23||Fused Silica||400 nm – 2 μm||400 nm – 1 μm||56 mm|
|II/FS42-47||Fused Silica||400 nm – 2 μm||400 nm – 2 μm||27 mm|
|II/ZS37-50||Zinc Selenide||2 μm – 18 μm||1 μm – 10 μm||14 mm|
The I/FS50-60 (and I/FS50-55, I/FS47-50) system uses the series I PEM. The Series l PEM has a rectangular shaped optic that, in essence, limits the useful aperture of the PEM. These small systems are practical when the light source has a small beam diameter. Therefore, if the application for the dual PEM involves a light source consisting of only one laser, this is a viable option.
The II/FS20-23 and the II/FS42-47 systems also employ high quality fused silica as the optical material and have a transmission range of 170nm to 2.6µm. Both models are completely functional in the visible and near IR light spectral regions. However, the II/FS20-23 system has the benefit of a larger aperture. This is especially useful if the light source has a large beam diameter or more than one light source is to be accommodated. This dual PEM is typically used in a Stokes polarimeter system to measure the orientation of the linear component of light emitted from a beam of deuterium atoms injected into tokamak plasma. The II/42-47 is also used in Stokes polarimetry measurements and provides a more compact optical head configuration.
The II/ZS37-50 has ZnSe as the optical material. This provides a modulating range from 2 μm to 18µm. This PEM pair has applications in the infrared region of the light spectrum. It can be used to analyze either a broadband light source or an infrared laser such as a CO2 laser.
Most of the Dual PEM systems utilize Series II PEMs, which employ octagonal shaped optical elements. The Series II PEMs meet higher requirements for polarization modulation and offer symmetrical distribution of PEM retardation over a larger aperture range.
Like all Hinds PEMs, these systems provide the unique benefit of a wide acceptance angle (> ± 20 degrees), good transmission over a wide wavelength range, high power handling capabilities, and a high polarization sensitivity. The table above compares the technical specifications for all of the standard Hinds dual PEM systems.
Antireflective Coating (ARC), Custom
Universal PEM Mount (UPM)
Special Calibration Option (SCO)
Special Frequency Option (SFO)