title  
 
 
Visible Imaging Stokes Polarimeter (VISP- instrument)
The main purpose
Instrument is designed for simultaneous production of four images of the space object, followed by calculation of the three Stokes parameters describing linearly polarized radiation. As the polarization analyzer in the instrument used by the polarizing film, set in the exit pupil of the telescope, which is formed by a collimator. The analyzer consists of four segments with different orientations of 0°, 45°, 90°, 135°.
Fig.1. The principle of imaging Stokes polarimeter
Specification
Telescope D=360…400 mm, D/f = 1/12...1/10

FOV , Angular of telescope / linear on detector

18’ x 18’/ 17x21mm (1.6”/px)
Effective focal length of the system   1200 mm
Instrument aperture ratio F#   11
Diameter of pupil   24 mm

Detector: Pixel size  / Total size

16x16 µm / 16,5ő20,4 mm

Spectral range  

Optimized for 0.41 –0,85  µm

Filters Position for 4 filters in wheel
System of filters replacement   Manual, possibility  of using a stepper motor
Diffraction grating   position for the transmission diffraction grating (100 lines/ mm)
Focusing system   Main mirror
Length of instrument   800 mm
Weight of instrument   6 kg
Short description
The polarimeter consistst of:
The collimator performs several functions: partial correction of field aberrations of the telescope, the construction of main mirror image (the pupil) with a diameter of 24 mm, and collimation of the radiation itself.
The analyzer of the polarization - the polarizing film, set in the pupil, formed by a collimator. The analyzer consists of four segments with different orientations of 0°, 45°, 90°, 135°, forming 4-channels.
The Space diversity system four pairs of achromatize wedges.
Spectral selection element – replacement filters or transmission diffraction grating with a frequency  to 100 lines per mm. Light diameter of replaceable elements (filters, gratings) is equal to 24 mm.
The camera lens - the simultaneous formation of four images on a detector. It consist of seven components and builds 4 image of sky in the different polarization. Figure 2 shows the location of the 4 images the sky on the camera.
Fig.2 Four images of the sky on the detector
Optical conceptual design

Fig.3 General view of the polarimeter optical layout

 

The function of the encircled energy concentration which characterizes the quality of the optical layout is presented in the Fig.4.  Spot size in the spectral range of 0,41-0,85 m for each point within the field of view 18 'x 18', which concentrates 95% of the energy of 32 ?m is, which corresponds to 2 pixels for the matrix. The maximum value of the distortion of the optical system of the Stokes polarimeter is 0.65%

Fig.4 The function of an encircled energy

Fig 5 Distortion of the system

 

Mechanical conceptual design

The mechanical design of the instrument is shown in Figure 6. Structurally, the Stokes polarimeter consists of the following units. Composite tube having sufficient rigidity, in which a collimator and block of removable diaphragm and slits are placed. The diaphragm or slit entered into the system manually. For panoramic observations with the maximum field of view 18 'x 18' the diaphragm with size equal  32x32 mm is using.

 
 
 

 

   
 
 
 
 
 
   
 

Optical engineering including research, design, development. Optimization, tolerancing, specifications of optical systems. Mechanical design, Finite Element Analysis (FEA).

©  2012-2014 Syniavskyi Ivan

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