Generation of Correlated Biphotons and Sensing with Long-Wavelength Radiation

To circumvent the difficulty of efficiently detecting long-wavelength radiation, quantum-sensing measurement techniques based on the effect of induced coherence without induced emission could be used. By means of correlated biphotons in a nonlinear interferometer, the hardly detectable radiation that illuminates the object under investigation is transferred to another wavelength range, for which sophisticated sensitive cameras exist. That way, the properties of idler photons can be measured indirectly by detecting only signal photons. In this work, this measurement principle has been extended to the terahertz spectral range and measurements with samples with the idler radiation propagating in free space were performed for the first time with this kind of radiation. Additionally, various advanced methods that allow to accelerate measurements in the near-infrared range have been developed in the context of this thesis.