Optimizing performance of quantum cascade laser-pumped molecular lasers

Quantum cascade laser-pumped molecular lasers (QPMLs) have recently been introduced as a new source of powerful (> 1 mW), tunable (> 1 THz), narrow-band (< 10 kHz), continuous-wave terahertz radiation. The performance of these lasers depends critically on molecular collision physics, pump saturation, and on the design of the laser cavity. Using a validated three-level model that captures the essential collision and saturation behaviors of the QPML gas nitrous oxide (N2O), we explore how threshold pump power and output terahertz power depend on pump power, gas pressure, as well as on the diameter, length, and output-coupler transmissivity of a cylindrical cavity. The analysis indicates that maximum power occurs as pump saturation is minimized in a manner that depends much more sensitively on pressure than on cell diameter, length, or transmissivity. A compact laser cavity with 10-100 times smaller volume than the nominally optimal geometry is able to achieve at least 95% of the maximum laser performance.