  Quantum cascade laser (QCL)-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 near-optimal compact laser cavity
can produce more than 10 mW of power tunable over frequencies above 1 THz when
pumped by a multi-watt QCL.
