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International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)

Generation of Quantum Correlated Optical - Terahertz Photon Pairs and Calibration of Nonlinear-Optical Detectors via Parametric Down-Conversion

Vladimir V. Kornienko, Kirill A. Kuznetsov, A.A. Leontyev, T. I. Novikova, G. Kh. Kitaeva

Published Sep 1, 2018• 0 citations
Publisher

Abstract

Quantum effect of parametric down-conversion is studied in a strongly frequency non-degenerate regime, when pairs of correlated optical and terahertz photons are generated along with parametric amplification and frequency conversion of thermal fluctuations and external radiation at terahertz frequencies. The terahertz photon fluxes emitted due to parametric down-conversion are registered. Direct incoherent nonlinear-optical detection is demonstrated for continuous wave sources at 0.2-0.4 THz.

DOI
10.1109/irmmw-thz.2018.8510353

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Frequency-angular characteristics of signal and idler photons generated under spontaneous parametric down-conversion are studied in a strongly frequency nondegenerate regime, without paraxial approximation, accounting for possible inherent absorption of idler waves in a nonlinear crystal, classical thermal field fluctuations, and the multimode character of parametric interaction induced by transverse spatial limitation of the pump beam. Spatial limitation is shown to lead to a huge increase in angular divergence of the idler photons generated at terahertz frequencies. General expressions are obtained for the frequency-angular sensitivity function of the nonlinear-optical terahertz wave detector and for power densities of the signal and idler photon fluxes. The absorption-induced difference in the parametric conversion coefficients for the noise and externally incident radiation of the idler frequency is shown to be described by approximately the same loss factor for all active spatial idler modes. Two different parametric contributions of the internal thermal noise to the number of output idler photons were revealed with different dependence on the idler-wave absorption. Expressions for the loss factors, which describe absorption-induced effects in signal and idler channels, are obtained and shown to be turning into one another by changing the sign of the absorption coefficient. Relative contribution of thermal and quantum field fluctuations into the intrinsic radiation of a nonlinear crystal at signal and idler frequencies is analyzed accounting for the crystal absorption properties.
Abstract Parametric down conversion in a strongly non-degenerate regime with output terahertz (THz) and optical beams is investigated. The theoretical approach based on the concept of independent Schmidt modes is developed and the shapes and weights of optical and THz Schmidt modes are analyzed both in a far-field and near-field regions. Analytical approximation for examined radial Schmidt modes is found. Strong azimuthal correlations between optical and THz photons are established. THz photons are shown to be involved simultaneously both in parametric down conversion and sum frequency generation processes. Photons in THz, Stocks and anti-Stocks channels are demonstrated to be strongly entangled. Methods to examine the properties of the THz radiation by measuring the correlations between generated Stocks and anti-Stocks components are suggested.