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Fingerprint authentication is a preferable biometric technique for securing images. Optical scanning cryptography (OSC) is a hybrid optical/digital method to encrypt and decrypt an image using optical scanning technique. In this paper, we propose a new strategy to combine OSC with fingerprints to enhance security. We have verified the effectiveness of the proposed idea in simulations. Subsequently practical implementation of the idea has also been performed with optical heterodyning to confirm the results from simulations. We have also discussed the added security and flexibility of implementation when optical heterodyning is employed in cryptography.

A detailed study of pulse shaping properties in crossed-beam volume gratings is performed. Analytical expressions for the profiles of the transmitted and diffracted beams are obtained based on the modified coupled wave theory. The spatial and spectrum evolutions and the diffraction efficiency of the diffracted pulsed beams are discussed. It is shown that the profiles of diffraction pulses and the total diffraction efficiency are greatly affected by the grating size, recording angle, and refractive-index modulation. The studies indicate that the shaping properties for different geometry parameters of the crossed-beam volume gratings are different. However, this difference can be used for many special pulse shaping applications.

Aluminum-doped ZnO (AZO) thin films are usually used as transparent conductors. For practical applications, however, the relatively high refractive index of AZO can lead to high optical reflection. In this work, we modified the optical properties of AZO thin films by adding different amounts of SiO2 into the AZO thin films to prepare the AZO-SiO2 composite thin films. The AZO-SiO2 films were deposited on quartz substrates using a co-sputtering deposition method. It was shown that the refractive index of the AZO-SiO2 thin films consistently decreased with the amount of SiO2 contained in the films. In the meantime, the resistivity of the AZO-SiO2 thin films was found to increase with the SiO2 content in the films. The effects of the deposition conditions on the optical and electrical properties of the AZO-SiO2 thin films were systematically investigated.

We have theoretically investigated the phase shift of a probe field for a four-level atomic system interacting successively with two fields tuned near an EIT resonance of an atom, a microwave field, and a coupling field. It has been found that the phase of retrieved signal has been shifted due to the cross-phase modulation when the stored spin wave was disturbed by a microwave. Because of the low relaxation rates of the ground hyperfine state, our proposed technique can impart a large phase rotation onto the probe field with low absorption of retrieved field and very low intensity of the microwave field.

The diffraction properties of volume holographic gratings are studied when the gratings are illuminated by an ultrashort pulsed beam with different polarization states. The developed coupled wave theory of Kogelnik is used. Considering the dispersion effect of the grating media, solutions for the diffracted and transmitted intensities, diffraction efficiencies and the bandwidths of the gratings are given in transmission volume holographic gratings and reflection volume holographic gratings. The bandwidths of the gratings are reduced by the dispersion effect of the grating media. They also have different influences on the diffraction of an ultrashort pulsed beam with different polarization states. For different values of the ratio of the spectral bandwidth of the input pulse to that of the grating, the changes of the spectral and temporal distributions of the diffracted intensities, as well as the diffraction efficiencies of the gratings are shown.

We have investigated the spectra of the electromagnetically induced transparency (EIT) when a cell is filled with a buffer gas. Our theoretical results show that the buffer gas can induce a narrower spectra line and steeper dispersion than those of the usual EIT case in a homogeneous and Doppler broadened system. The linewidth decreases with the increase of the buffer gas pressure. This narrow spectra may be applied to quantum information processing, nonlinear optics and atomic frequency standard.