Statistical distributions of the analog readings of an antenna-coupled THz superconducting bolometer were measured and analyzed under a special type of irradiation by low-energy fluxes of THz photons with Poisson photon statistics and controllable mean photon numbers. The photons were generated via low-gain parametric down-conversion in pulse-pumped Mg:LiNbO₃ crystal placed to a cooled cryostat together with the bolometer NbN film. Results of theoretical approximation of experimental histograms reveal the discrete nature of THz detection by superconducting bolometers and open a way for studying their quantum characteristics. It is shown that bolometer readings per pulse consist of discrete counts (“single charges”), with the mean number linearly dependent on the number of input photons. Contributions of single counts to a total analog reading are statistically distributed according to the normal law, with average values slightly depending on the number of counts in each reading. A general formula is proposed to describe the relationship between continuous statistical distribution of the bolometer readings and discrete quantum statistics of the incident photons.

The terahertz wave generation by spiral photoconductive antennas fabricated on low-temperature In_0.5Ga_0.5As films and In_0.5Ga_0.5As/In_0.5Al_0.5As superlattices is studied by the terahertz time-domain spectroscopy method. The structures were obtained by molecular beam epitaxy on GaAs and InP substrates with surface crystallographic orientations of (100) and (111)A. The pump-probe measurements in the transmission geometry and Hall effect measurements are used to characterize the properties of LT-InGaAs and LT-InGaAs/InAlAs structures. It is found that the terahertz radiation power is almost four times higher for LT-InGaAs samples with the (111)A substrate orientation as compared to (100). Adding of LT-InAlAs layers into the structure with (111)A substrate orientation results in two orders of magnitude increase of the structure resistivity. The possibility of creating LT-InGaAs/InAlAs-based photoconductive antennas with high dark resistance without compensating Be doping is demonstrated.

The conditions for the generation and detection of quantum-correlated pairs of optical and terahertz photons in the process of strongly frequency-nondegenerate parametric down-conversion of light are investigated. An approach based on increasing the frequency of the optical pump is proposed, whereby the power of a weak flux of terahertz idler photons can be measured for a wide range of parametric gain coefficients, down to the onset of the spontaneous down-conversion regime, using the same terahertz detector with a limited dynamic range. It is shown experimentally that the doubling of the frequency of pulsed laser pump leads to a 5-fold reduction in the lowest value of parametric gain that is still sufficient for detecting terahertz idler photons with a cooled hot-electron bolometer.