partOf Configuration for THz absorption spectroscopy: tunable THz QCL in continuous-wave mode; QCL operating temperature 44.30 K or 54.45 K with <5 mK stability; laser frequency tuned by linearly ramping input current from a laser driver controlled by a function generator providing 10 Hz sawtooth waveforms; phase-locked optical chopper at 5 Hz; collimated beam diameter ~3 mm; laser beam path at ~18 mm above RF electrode; effective absorption length 84 cm
