ИСТИНА

We propose to use a pair of the periodically poled crystals with different periods for narrow-band generation and frequency-matched narrow-band detection of the terahertz-range radiation. Generation scheme via eee-geometry optical rectification of the broadband near-infrared laser radiation, detection scheme via ooe-geometry difference frequency conversion of the visible laser radiation, and optimal parameters of domain structures in Mg-doped and undoped lithium niobate crystals are considered. It is shown that, at the initial low-gain stages of all frequency conversion processes, the impact of any one-dimensional spatial structure of medium non-linearity can be described in terms of a single functional parameter, nonlinear transfer function (T-function) [1]. Expressed in terms of dimensionless phase mismatches, the T-function can be measured once in some process convenient for measuring, and further applied in another process, provided that the refractive indexes and dispersion of the medium are known. As one of the most informative for the T-function characterization, we propose a method based on the measurement of the two-dimensional frequency-angular spectra of spontaneous parametric down-conversion [2-4]. We use this method for characterization of the terahertz-range capabilities of our crystals with Czochralski-grown periodically poled structures.