A new technique for directly extracting phase gradients from two-dimensional (2-D) interferometer fringe data is presented. One finds the gradients by tracking the maximum modulus of the continuous wavelet transform of the fringe data and the phase distribution that is obtained, with a small error, by integration. Problems associated with phase unwrapping are thereby avoided. The technique is compared with standard methods, and excellent agreement is found. In common with Fourier-transform methods, the technique is capable of extracting the full 2-D phase distribution from a single image.

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A suite of zwitterionic pyridylidene-based merocyanines that contain no interconnecting p-bridge between the donor and acceptor rings has been synthesised and their second-order NLO properties evaluated largely by semi-empirical computational methods (MOPAC 97/AM1). Contrary to expectation, increasing the degree of inter-ring twist (h), at least up to 55u, in these new pyridylideneazolone chromophores is found to have little or no effect on the figure of merit [mb( 0 )]. An X-ray crystallographic appraisal of one of these chromophores, 14, reveals however that the twist angle (albeit in the solid state) is greater than that predicted by computation and that all other features are consistent with the highly zwitterionic nature of these systems. In spite of this, a combination of factors-insufficient acceptor strength, insufficient extent of conjugation and perhaps insufficient twist angle, in particular-clearly leads to the low values of the quadratic hyperpolarisabilities. The trade-off between targeting a more modest b from a minimum of p-conjugating framework between D and A (and therefore synthetic expediency) and seeking a moderate-to-high dipole moment has therefore resulted in only low figures of merit for these systems.Calculations performed on a suite of readily accessible, isoelectronic cyanines, in which the acceptor is a stabilised cyclopentadienide carbocycle rather than a heterocycle, have revealed the potential that these systems, exemplified by 27, have as NLO chromophores. Representative polymer-tetherable derivatives of this system have been prepared as have the corresponding TDI-based polyurethanes.

We used a commercially available liquid crystal television display unit as a spatial optical phase-only modulator. To do this, we removed the integral polarizers from the unit and double passed the light under modulation through it. We found that it was possible to obtain continuous phase modulation from 0 to PI with essentially no change in the state of polarization of the output light and absorption changes of <2.5%. We wrote computer-generated phase-only holograms on the LCTV and reconstructed them optically.

A novel adaptive wave-front correction system based on an all-optical feedback interferometer is described. In this system the two-dimensional output fringe intensity from a Mach-Zehnder interferometer with large radial shear is optically fed back to an optically addressed phase-only liquid-crystal spatial light modulator. Consequently, without a separate aberration-free reference wave, the modulator phase approximates the conjugate of the interferometer phase that is directly related to the phase of the input aberrated wave front, so this system is applicable in adaptive optics. We successfully achieved real-time correction of aberrated wave fronts: A diffraction pattern that was seriously distorted because of aberrations was transformed into a diffraction-limited spot immediately after the feedback loop was closed.