Photoanisotropic incoherent-to-coherent optical conversion

All-optically phase-induced polarization modulation by means of holographic method

Phase-induced polarization modulation has been achieved experimentally by means of the all-optical holographic method. An extra spiral phase is added to a Gaussian beam and then a holographic grating is recorded through the interference of a Gaussian beam and the phase-vortex beam with the same linear polarization state in an azobenzene liquid-crystalline film. We report here that the polarization state of the diffraction light from the recorded grating is different from that of the incident light, while no polarization variation occurs for the holographic grating recorded by two Gaussian beams. The phase-induced polarization modulation is mainly attributed to the formation of birefringence in the film generated by phase vortex, which is investigated through the ripple patterns resulting from the competition between photoinduced torques and analysed by the Jones matrix. The experimental results could enrich the connotation between optical parameters and offer a method to realize polarization modulation through phase control.

Revisiting Bragg's X-ray microscope: scatter based optical transient grating detection of pulsed ionising radiation

Transient optical gratings for detecting ultrafast signals are routine for temporally resolved photochemical investigations. Many processes can contribute to the formation of such gratings; we indicate use of optically scattering centres that can be formed with highly variable latencies in different materials and devices using ionising radiation. Coherent light scattered by these centres can form the short-wavelength-to-optical-wavelength, incoherent-to-coherent basis of a Bragg X-ray microscope, with inherent scope for optical phasing. Depending on the dynamics of the medium chosen, the way is open to both ultrafast pulsed and integrating measurements. For experiments employing brief pulses, we discuss high-dynamic-range short-wavelength diffraction measurements with real-time optical reconstructions. Applications to optical real-time X-ray phase-retrieval are considered.

Edge enhancement and image equalization by unsharp masking using self-adaptive photochromic filters

A new method for real-time edge enhancement and image equalization using photochromic filters is presented. The reversible self-adaptive capacity of photochromic materials is used for creating an unsharp mask of the original image. This unsharp mask produces a kind of self filtering of the original image. Unlike the usual Fourier (coherent) image processing, the technique we propose can also be used with incoherent illumination. Validation experiments with Bacteriorhodopsin and photochromic glass are presented.

Spatial self-filtering with polarizer sheets

A method for phase visualization and edge enhancement by spatial self-filtering by use of a polarizer sheet in the Fourier plane of an optical processor is described. Light absorbed by the polarizer sheet induces a thermal lens, which, in turn, produces selective action on certain spatial frequencies of the image to be processed. Some experiments that demonstrate the self-filtering action of the proposed system are presented.

Polarization gratings with surface relief in dyed gelatin and their postdevelopment diffraction

Some characteristics of dyed gelatin films when polarization gratings are recorded are reported. Two dyes, Malachite Green and Methylene Blue, are used in our experiment. In particular, no dichromate was added to Methylene Blue plates before or after exposure. It is shown that, in spite of its having high viscosity, a relief grating is formed when orthogonal linearly polarized beams are superimposed upon the plates. In contrast with previous observations in another photoanisotropic medium, the frequency of the gelatin relief grating does not depend on the directions of the electric field of the orthogonal recording beams. Besides, when orthogonal circularly polarized beams are used in the formation of polarization gratings, no relief grating is produced. Finally, we study the phase modulation obtained after dehydration of the gelatin plates in which the polarization gratings were formed. Postdevelopment phase gratings do not preserve the polarization information of the interference pattern. Also, the grating frequency is increased by a factor of 2 for linear polarization, whereas for circular polarization there is no phase modulation.

Self-adaptive spatial filtering by use of azo chromophores doped in low glass-transition-temperature polymers

We report on self-adaptive spatial filtering by combination of the self-adaptive polarization-rotation property of Disperse Red1-doped polymers with low glass-transition-temperature and Fourier-transform operation. Our system can be operated with only an action beam with object information and without a probe beam for image readout. Edge enhancement by the action beam-probe beam is demonstrated as an example of the system's application to spatial filtering.

Real-time enhancement of defects in periodic patterns by use of a bacteriorhodopsin film

We present a real-time optical system to enhance defects in periodic patterns by use of nonlinear spatial filtering by real-time holography. A straight and equispaced grating written in a bacteriorhodopsin film is read by the Fourier transform of a periodic pattern to be inspected. Because the diffraction efficiency of the grating depends on the intensity of the reading beam, only the defect component can be selectively diffracted and imaged. This system is applicable even to moving objects. We present experimental results that show enhancement of defects as small as 10 microm in a photomask with a pixel pitch of 150 microm used for a liquid-crystal display.

Photoanisotropic incoherent-to-coherent converter using a bacteriorhodopsin thin film

We have fabricated a novel optically addressed spatial light modulator by using bacteriorhodopsin immobilized in a polymer thin film. This incoherent-to-coherent converter is based on photoinduced anisotropy, as distinguished from previously reported devices based on photochroism in bacteriorhodopsin. This system is capable of a resolution of 114 lines/mm with a contrast ratio of 100:1.

Real-time joint transform correlation with photoanisotropic dye-polymer films

The results of joint transform correlation with photoanisotropic organic materials are presented. The materials' dynamic holographic recording capability and high resolution permit the operation of such a correlator in real time. Both theoretical and experimental results show that the photoanisotropic properties cause a dependence of the correlation output on the state of the polarization of the readout beam and can be used to produce an output polarization orthogonal to the input, which permits polarization filtering to be used, greatly increasing the signal-to-noise ratio. The effect of the saturation of the nonlinearity on correlation performance is investigated and is shown to be able to improve correlator recognition and discrimination. The correlation results of binary images and of a highresolution synthetic-aperture radar image are presented, demonstrating excellent optical quality, nonlinear edge enhancement, and real-time operation.