Fast gating or shuttering of light through a large aperture is possible with a HOE (Holographic Optical Element) written into new novel materials such as, but not limited to, EO (Electro-Optic) polymers. These materials can be non-birefringent thin or thick films applied to an optical substrate of a square centimeter or larger. The refractive index of EO polymers can be switched fast (10 to 100 nanoseconds) by applying an electric field across the film, perpendicular to the plane of the optical substrate. Changes in refractive index can be up to a few percent which allow a holographic grating to accept or reject the light. These new novel materials are available from several research sources such as the University of Arizona and the University of Washington. These materials are currently being studied and tested as electro-optic polymer modulators with very small apertures (~1 mm) and operating at longer wavelengths than visable (e.g.1550nm). Gating non-collimated light can be accomplished with an additional HOE operating as a beam-shaping collimator. We plan to utilize existing holographic technology to build an optimised collimator for this project. Collected input light would first pass through the beam-shaping collimating HOE and then be gated with the EO-polymer-HOE. This would simultaneously meet FOV requirements and gating requirements.
Benefit: There are several anticipated benefits of creating a device that can gate (e.g. off/on/off) light through a large aperture. The device would provide protection for expensive, high-sensitivity detectors such as photomultipliers (PMTs) and intensified photodiodes (IPDs) by only allowing light to pass to the detectors during the interval of interest. Essentially all background light, which creates a large continuous response from a detector, would be eliminated. In addition the device could block light to a detector when the device (and sensing system) is powered off, thus providing exposure protection during all times except when making a measurement (e.g. standby, transit, storage). This would provide useful protection from permanently damaging and short-term degratating exposures from ambient sources such as sunlight and moonlight. However, the proposed device is not intended to protect against direct exposure from a continuous wave or pulsed laser source. The device would also allow optical demodulation of light down from frequencies approaching 100MHz. Potential commercial applications are numerous since many sensing applications utilize photocathode based high-sensitivity detectors. Example application areas include: aerial laser radar (lidar) surveying for topographical mapping, atmospheric and environmental measurement lidars, and medical optical imaging applications.
Keywords: Detectors, Detectors, gating, LIDAR, electro-optic, Photomultiplier, Polymer, Image-intensifiers, Photocathode
