Stress Plate Optical Modulator for Circular Dichroism Measurements

The fused silica stress plate modulator described below offers several advantages over the other known electrooptic modulation devices: primarily, high transmission over a broad wavelength range, and large aperture. When operated at its electromechanical resonance frequency of 16.7 kHz, the modulator requires only low voltage, low power drive to operate as a +/-lambda/4 plate. Complete constructional details are given, including a model from which resonance frequencies may be calculated. As part of a circular dichroism apparatus, the modulator has allowed measurement of effects as small as 1 part in 10(5). The possibility of extension of the operating range into the vacuum uv is discussed.