Spectrally Selective Shutter Mechanism

Several state-of-the-art detection and image systems require synchronous high-speed shuttering of incoming irradiance. This shuttering action is necessary in many instances to increase signal-to-noise ratio, obtain high-speed (low-retention) imagery, and provide single-event observations. Presently, this type of "snap-shot" imagery is approximated by rotating chopper wheel methods that sweep an aperture across the focal plane. At faster aperture rates, these mechanical chopper systems become more complex and maintenance of image fidelity is very difficult. This novel, spectrally selective shutter mechanism provides true "snap-shot" imagery. Despite some limitations, such a mechanism is ideally suited to high flux, high background, and rapidly changing imaging visualization, and can be used to monitor flow visualization, chemiluminescence phenomena, and laser operation. The optomechanical techique described in this paper uses the rotation of one or two narrowband spectral filters to provide open-shutter times in the millisecond range. The resulting performance of the two-filter assembly is governed by the physical principle that increasing angular tilt of a narrowband interference filter causes the bandpass parameter to shift progressively toward shorter wavelengths. Data presented in this paper demonstrate that the spectral shutter technique can provide repetitive open-shutter times in the low-millisecond range, with true "snap-shot" images synchronized to video rates. Both advantages and limitations of this spectrally selective shutter are discussed and compared to typical mechanical chopper wheel methods. Specifically, performance advantages include the capability to provide (1) "snap-shot" imagery that always encompasses the entire field of view, (2) self-contained spectral selectivity for focused signal irradiance, (3) greater transmission efficiency during open-shutter times, and (4) adaptability to a wider variety of optical systems.