Аннотация:Possible effects caused by the presence of classical thermal field fluctuations and
inherent absorption of the non-linear crystal at THz frequencies were investigated
using the theoretical approach based on generalized Klyshko-Kirchhoff law. The
huge angular diversity of SPDC-generated THz photons was studied both
theoretically and experimentally. Comparatively greater progress has been
achieved in detecting optical photons, which are emitted at small Stokes shifts,
correlate with their THz counterparts, and can provide information on THz properties
of matter without direct detection of THz waves. However, for a vast majority of
attracting applications (ghost imaging without THz cameras, absolute calibration of
quantum efficiency of THz detectors, and other tasks), the direct measurement of
optical-terahertz correlation function g(2) is important. The solution to this problem is
significantly complicated by the lack of current THz receivers capable of operating in
the single-photon mode and high-speed coincidence circuits. First results of g(2)
measurement using analog readings of an idler THz receiver (a superconducting
NbN bolometer) and a signal optical detector (a photo multiple tube) are discussed.