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We report pulsed laser studies of nonlinear luminescence in a platinum ethynyl complex which, from 560 to 700 nm, shows strong two-photon absorption from the ground singlet state to an excited singlet state. The spectral dependence of the photoluminescence peaks indicates that in the region from 560 to 700 nm the two-photon absorption cross section is independent of excitation wavelength. Through the use of a simple calibration we have been able to estimate the number of states (NS1) formed from two-photon absorption, and have found good agreement with theory using the value of β=0.34 cm/GW measured previously.

A double-element broad-band liquid crystal tunable filter consisting of a high-order quartz wave plate in series with a very-low-order electrooptically tunable liquid crystal phase plate and placed between crossed polarizers is described. A possible application for such a device is protection against intrusive laser radiation. The advantage of this double-element filter over a single-element low-order LC filter is that it increases the wavelength resolution of the device, which, when operated in the protect mode, allows continued sensing of the scene. Experimental and theoretical studies were made of the contrast ratios obtainable with such a filter. >

Broadband electro-optically tunable filters have uses in applications such as wavelength de-multiplexing and laser light detection and filtering. The materials requirements for such devices are that they must have a very low absorption over the wavelength region of interest, have a large electro-optic coefficient and be easily engineered into optical components. Liquid crystals satisfy these criteria.

Complete ZnSe interference filters exhibiting optical bistability have been fabricated using ultrahigh-vacuum molecular-beam techniques. The wavelength dependence of the critical switching power wa...

Optical studies were carried out at 647 nm in a Fabry-Perot etalon containing the liquid crystal mixture 3/5/7 PCH. The electro-optic and nonlinear effects were brought together in two sets of experiments. Firstly, optical bistable loops were obtained at different initial cavity tunings imposed by the applied voltage through the electro-optic effect. Secondly, bistable switching was achieved by fixing the input optical power and varying the voltage to obtain “voltage bistable” loops. The behaviour of these loops was found to follow the trend predicted by theory.

This paper reviews the different types of optical bistability in II–VI semiconductor compounds with particular emphasis on experimental results obtained in CdHgTe, CdTe and ZnSe. Results of optical bistability in an entirely molecular beam deposited ZnSe filter are presented for the first time.

Ultrahigh vacuum and molecular beam deposition techniques have been used to fabricate ZnSe interference filters. These demonstrate optical bistability with critical switching power being measured at five wavelengths between 521 and 676 nm. These filters demonstrate considerably improved long term operation stability over that offered by samples deposited using conventional thermal evaporation. Both dispersive and absorptive bistability could be demonstrated in the same sample.