Terahertz optical properties of potassium titanyl phosphate crystals.

This paper studies the terahertz optical properties of nonlinear potassium titanyl phosphate crystals with different conductivities in the spectral range of 0.2 to 2.6 THz. The observed properties are characterized by several absorption lines lying along different optical axes which represent the relevant potassium sublattice phonon modes. The peculiarities of these absorption lines are attributed to the structural order of potassium ions.

Incoherent diffraction correlator with a holographic filter.

An incoherent optical method for spatial frequency filtering is considered, based on the principle of diffraction in spatial incoherent monochromatic light. Such a method is shown to be possible in an incoherent diffraction correlator with a holographic filter. This permits substantially lower requirements for the adjustment accuracy of the system, significantly decreased required dynamic range of the holographic filter, and the phase distortion influence on the form of an output correlation function is canceled. It is shown that, for completely incoherent processing, the filtering process is invariant to longitudinal shift of the holographic filter. The influence of incomplete phase modulation on the form of output correlation function is discussed as it is used to distort spatial coherence. This case is shown to be analogous to the processing in partially coherent light. Dependence of SNR on the depth of phase modulation is obtained.