18 August 2005 Off-resonance properties of a photoelastic modulator
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Polarization modulation in photo-elastic modulators (PEM) driven on and off resonance has been investigated for a commercially available PEM using a high speed infrared (lambda=1550 nm) polarimeter. Off-resonance operation was explored in the hope of finding a slower operating mode than the primary resonance. The primary resonance, used for normal PEM operation, was 5 Hz wide with a Q of 8500. The phase transfer function was well behaved and typical of electrical resonances. Device startup and shutdown had smooth amplitude changes occurring over 1/3rd of a second. The photo-elastic modulator was examined at drive frequencies significantly below the resonant frequency. Driving the PEM with several odd sub-harmonics generated resonance at the fundamental frequency. Three other lower frequency resonances were discovered, but all at an oscillation amplitude more than 12 db below the amplitude of the fundamental resonance. Thus a practical configuration to allow slower operation of the PEM was not found.
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Karlton Crabtree, Karlton Crabtree, Neil Beaudry, Neil Beaudry, Russell Chipman, Russell Chipman, "Off-resonance properties of a photoelastic modulator", Proc. SPIE 5888, Polarization Science and Remote Sensing II, 58880A (18 August 2005); doi: 10.1117/12.621527; https://doi.org/10.1117/12.621527


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