Use of stimulated scattering by polaritons in detection of submillimeter radiation

An experimental investigation was made of a detector of submillimeter radiation utilizing a difference frequency generated as a result of stimulated scattering by polaritons in a crystal of lithium niobate. When the pump pulse duration was 2τ_p = 18 nsec and the cross-sectional area of the pump beam was Q_p=0.17 cm², about 4×10⁵ photons with frequencies in the range 25–35 cm^–1 were detected in a solid angle Ω = 10 msr for the signal/noise ratio of 5. The experimental results were in qualitative agreement with theoretical estimates obtained allowing for the finite apertures of the interacting waves.