High Speed Photoelastic Modulation

Abstract

An inexpensive and easily constructed device for the high speed rotation of the plane of polarization of a beam of monochromatic plane polarized light has been demonstrated.The device can be successfully used as an optical chopping device for polarized light at speeds between 20 KHz and 4 MHz or to introduce any other retardance leading to circular or elliptical polarization forms. The optical extinction/transmittance pattern for the half-wave operation, although not truly sinusoidal, has been mathematically determined. To drive the modulation, a high precision sinewave generator capable of automatic gain and frequency compensation is recommended; however, the device can be used successfully with almost any sinewave generator. Voltage requirements increase as the wavelength of the light increases and varies between 10V and 200V dependent upon the wavelength of light used and the multiple of the fundamental drive frequency desired. These voltages can be obtained from many wideband amplifiers currently available.