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As an optical component, a hybrid cell includes a photorefractive window and a layer of liquid crystal (or polymeric material). In existing hybrid photorefractives, the evanescent space-charge field from a photorefractive window induces a change in the refractive index of adjacent layers of liquid crystal. As a result, the evanescent photorefractive space-charge field increases the overall index modulation by inducing an additional index modulation in nearby high birefringence material(s) which may or may not themselves be inherently photorefractive. This penetration of the space-charge field into the liquid crystal layer changes the director alignment of the liquid crystal molecules, creating diffractive beam coupling within the liquid crystal layer. The unidirectional coupling of one beam to the other leads to increased power. Hybrid cells have been developed but their utility has been limited by the relatively small magnitude of the available space-charge field. Improvements will be based on increasing the space-charge field or improving the sensitivity of the liquid crystal or polymer layers to the influence of the electric field.
Answering this need for improved performance, Air Force researchers have developed a hybrid device with a liquid crystal layer having a 45 degree pre-tilt and low anchoring energy. This approach increases the sensitivity of the liquid crystal to the space charge field. The liquid crystal gain contains nanoparticles in a solid or gel form and may be either active or passive (and inorganic or organic) in nature. In one iteration, the nanoparticles are ferroelectric and have a pronounced effect on the gain characteristics, sensitivity, birefringence, speed, and photorefractive beam coupling of the hybrid cell. Additionally, the Air Force approach permits transient or steady state optical interactions with thermally absorbed radiation, optical fields, acoustic radiation, and induced electrostriction.
US patent 8,018,648 is a divisional of US patent 8,369,006.
- The addition of the ferroelectric nanoparticles may result in a complete reversal of the sign of the beam coupling gain
- Maximum gain coefficient of approximately 1100 cm−1, an extremely large value for Bragg matched two-beam coupling
- US patent 8,018,648 available for license