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Intensity Control System using Crossed Linear Polarizers

IP.com Disclosure Number: IPCOM000091093D
Original Publication Date: 1969-Oct-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Lemke, LT: AUTHOR

Abstract

The system provides a calibrated variable light intensity using sheets 10 and 11 of polarizing material located between light source 12 and detector 13. Sheet 11 is rotatable while sheet 10 is stationary. Sheet 11 can be adjusted to have its axis A of polarization at angle theta with respect to the axis B of polarization of sheet 10. Light transmission through sheets 10 and 11 can be changed by rotating sheet 11. Such transmission varies as COS/2/ theta. To calibrate, for example, photodetector 13 of the silicon type having a spectral response from 400 to 1,200 nanometers, sheets 10 and 11 can be of material that polarizes in the infrared region from 600 to above 1,200 nanometers and is opaque in the visible region from 300 to 600 nanometers.

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Intensity Control System using Crossed Linear Polarizers

The system provides a calibrated variable light intensity using sheets 10 and 11 of polarizing material located between light source 12 and detector 13. Sheet 11 is rotatable while sheet 10 is stationary. Sheet 11 can be adjusted to have its axis A of polarization at angle theta with respect to the axis B of polarization of sheet 10. Light transmission through sheets 10 and 11 can be changed by rotating sheet 11. Such transmission varies as COS/2/ theta. To calibrate, for example, photodetector 13 of the silicon type having a spectral response from 400 to 1,200 nanometers, sheets 10 and 11 can be of material that polarizes in the infrared region from 600 to above 1,200 nanometers and is opaque in the visible region from 300 to 600 nanometers. Source 12 can be s tungsten lamp providing light from below 400 nanometers to above 1,200 nanometers. Alternatively, sheets 10 and 11 that polarize in the visible region from 300 to 600 nanometers but not in the infrared region above 600 nanometers can be used with source 12, having its output limited to the visible region, such as an HeNe laser. In both cases, the spectral content and angular distribution of light from source 12 remain fixed as the intensity of light is changed on detector 13 so that the intensity of light on detector 13 can be precisely controlled. Likewise, accurate calibration of detector 13 can be obtained, assuming that the maximum light intensit...