Electro-optical processor for measuring displacement employing the Talbot and the nonsteady-state photo-electromotive force effects.

We present a device for measuring displacement based on the Talbot and the nonsteady photo-electromotive force effects. The proposed device does not require any numerical signal processing since its output signal is, in appropriate regions, linearly related to the measured displacement. The proposed system requires an illuminating field with a sinusoidal amplitude distribution and low fringe visibility. The dynamic range can be adjusted according to the illuminating field spatial period or wavelength. Displacements with an estimated resolution better than 10 µm in a dynamic range of 1.5 mm were detected using a sinusoidal amplitude grating with a period d=100 µm.

Holographic generation of a class of nondiffracting fields with optimum efficiency.

We discuss the accurate generation of complex optical fields using phase holograms that provide the optimum diffraction efficiency. In each considered case, the phase modulation of the employed hologram is identical to the phase of the desired optical field. We show that periodic and quasiperiodic nondiffracting optical fields, mathematically obtained through the superposition of multiple plane waves, can be generated with high fidelity using this approach.

Polarization-controlled contrasted images using dye-doped nematic liquid crystals.

We explore the polarization dependence of the nonlinear response of a planar nematic liquid crystal cell doped with 1% wt of methyl red dye. The results obtained show that the refractive index change can be switched from a positive value to a negative one as the polarization of the beam changes from parallel to perpendicular with respect to the rubbing direction. This property is exploited in a phase contrast system, where a dynamic phase filter is photoinduced in a liquid crystal cell placed in the system's Fourier plane. Real-time contrast inversion in the resulting images is demonstrated.

Incoherent-to-coherent conversion and square-law transmission based on photoinduced birefringence in bacteriorhodopsin films.

We review the main optical properties of bacteriorhodopsin that are relevant to its use as a spatial light modulator. A model is described for the transmittance of a film placed between crossed polarizers in which photoinduced birefringence occurs. We show when the transmittance is proportional to the write intensity. We use this property in a joint transform correlator for incoherent-to-coherent conversion and effective square-law modulation in the Fourier plane.