Concurrent Terahertz Generation via Quantum Interference in a Quadratic Media

The strive for efficiency in the generation of terahertz (THz) waves motivates intense research on novel field-matter interactions. Presently, THz generation via quadratic crystals remains the benchmark thanks to its simple and practical deployment. An interesting problem is whether new mechanisms can be exploited to elicit novel generation approaches and forms of control on the THz output in existing systems. THz generation via quantum interference (QI) leverages a third-order nonlinear response under resonant absorption, and it has been recently explored to access surface generation in centrosymmetric systems. Its deployment in standard THz quadratic sources can potentially create a physical setting with the concurrence of two different mechanisms. Here, THz generation via QI in noncentrosymmetric crystals concurrent with phase-matched quadratic generation in a bulk-transmission setting is demonstrated. Beyond investigating a new physical setting, it is demonstrated that conversion efficiencies much larger than those typically associated with the medium become accessible for a typically adopted crystal, ZnTe. An inherent control on the relative amplitude and sign of the two generated THz components is also achieved. This approach provides disruptive boost and management of the optical-to-THz conversion performance of a well-established technology, with significant ramifications in emerging spectroscopy and imaging applications.