Multicycle Terahertz Generation Using High-Energy Pulse Trains

Frequency conversion in nonlinear crystals is a well-established method to provide narrowband, multicycle terahertz (THz) radiation for applications requiring high spectral purity like spectroscopy and electron acceleration [1], [2]. While significant progress has been made by using laser systems that produce pairs of narrow spectral lines separated by the THz frequency, optical-to- THz conversion efficiencies still remain below one percent [3], [4]. However, simulations have shown that multiple-percent efficiencies are achievable if the pump spectrum is composed of several lines [5]. In the time domain this corresponds to a regular train of pulses spaced by the inverse THz frequency. Here, we experimentally explore the parameter space of a new approach to multicycle THz generation based on tunable pulse trains and demonstrate its potential to boost conversion efficiencies.