Theoretical exploration of sensitive terahertz detection by cascaded difference-frequency generation

Nonlinear optical frequency conversion technologies, including the optical parametric process and difference-frequency and sum-frequency processes, have demonstrated good performance for terahertz (THz) wave detection. The quantum efficiencies of the above technologies cannot break through the Manley–Rowe limit. In this work, we present a novel scheme for THz wave detection based on cascaded difference-frequency generation in combination with optical parametric oscillations. By superimposing a weak THz wave and an intense pump wave in an aperiodic periodically poled lithium niobate crystal, a series of Stokes waves and a series of anti-Stokes waves are generated. The Stokes waves oscillating in a resonant cavity are transferred to high-order Stokes waves continuously and repeatedly. The high-sensitivity THz wave detector is realized by measuring the intensities of the Stokes waves or the enlarged THz wave. This research enables a comprehensive understanding of the physics of the cascading second-order nonlinear detection and provides a worthy reference for subsequent experimental design.