optical instruments
stokesmeter™ polarimeter


 

 

stokesmeter™ polarimeter description
The StokesMeter is a advanced approach to the measurement of polarized light. This device uses no moving parts and no modulators to quickly and accurately determine the complete polarization state, or change in polarization of an unknown input beam.

 

 

abstract
A photopolarimeter for the simultaneous measurement of all four Stokes parameters of light. The light beam, the state of polarization of which is to be determined, strikes, at oblique angles of incidence, three photodetector surfaces in succession, each of which is partially spectrally reflecting and each of which generates an electrical signal proportional to the fraction of the radiation it absorbs. A fourth photodetector is substantially totally light absorptive and detects the remainder of the light. The four outputs thus developed form a 4x1 signal vector I which is linearly related, I=AS, to the input Stokes vector S. Consequently, S is obtained by S=A(-1)I. The 4x4 instrument matrix A must be nonsingular, which requires that the planes of incidence for the first three detector surfaces are all different. For a given arrangement of four detectors, A can either be computed or determined by calibration.

 

features

  • Fastest possible instrument for polarization measurement

  • Real-time measurement and display of Stokes parameters

  • Easy menu-driven alignment and operation

  • Muller matrix ellipsometry possible

  • High sampling rate and fast response time

  • Rugged - no moving parts

  • Small, compact measurement head

  • Simple operation

 

computer interface
Using a Windows VISA/XP/2000 computer, the StokesMeter displays polarization information in a number of familiar formats, all of which are based on the four parameters of the Stokes vector. Its built-in high speed data acquisition system can read and display complete polarization information in a fraction of a second. 

Shown below are actual screen displays:

shown above are the: 

  • Poincare Sphere

  • Polarization Ellipse

  • Stokes parameters s0, s1, s2 and s3

  • Azimuth and Ellipticity Angle

  • Axial Ratio

  • Degree of Polarization

The Poincare sphere representation gives a quick and easy-to-understand 3 dimensional visualization of the complete state of polarization based on the 4 Stokes parameters s0, and normalized s1, s2 and s3. The polarization ellipse is the familiar 2 dimensional representation of the polarization state of the measured input beam.  

Rapid  sampling of the normalized Stokes parameters s0, s1, s2 and s3 permits the polarization state to be statistically monitored  so more complicated aspects of stability, drift and noise can be recorded, analyzed and displayed.

 

 

This screen displays the StokesMeter alignment with respect to the measured laser beam

 

 

This screen displays the StokesMeter calibration matrix together with detailed sensor information. 

Constructing a new calibration matrix requires additional optional components of a 360º polarizer circle containing a Glan Thompson prism, a quarter wave plate mounted in a 360º circle and an additional detector (about $5K). 

 

stokesmeter polarimeter specifications

Calibration wavelength: HeNe 632.8nm laser under 1 mW  (other laser wavelengths optionally available)
Clear aperture: 1 mm diameter
Measurement speed: Few Milliseconds
Maximum absolute error: .02 of a Stokes parameter
Absolute error (averaged): .008 of a Stokes parameter
Computer (not included): Windows 7/VISTA/XP/2000 with an available PCI slot
Operating temperature: 72°F
Weight: Approximately 8 lbs.
Power requirements: PCI interface card is powered by your computer
Size: Approximately 4" x 6" x 12"

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