Knowledge Bank

A cylindrical cavity sample cell with ends that transmit 80% of the incident infrared radiation has been constructed for the purpose of carrying out infrared microwave double resonance experiments with high-power microwave pumping radiation and a tunable low-power infrared source. The length of the cavity and the microwave injection port are tunable and the measured Q is $\sim 5000$. The microwave pumping source is an 8-12 or 12-18 GHz backward-wave oscillator that is amplified to as much as 20 W by means of a traveling wave tube amplifier. The ends of the cell are high-transparency fine mesh metal screens covered by NaCl windows. The path length is 0.3 m. The infrared source is an infrared microwave sideband laser operating in either the $6\mu m$ or $10\mu m$ region. The purpose of the high-power pumping is to create a Rabi splitting of the pumped transition that is comparable to the Doppler width, so that the modulation of the infrared absorption caused by switching the microwave power has a magnitude that is a significant fraction of the ordinary infrared absorption. The results of experiments with $CH3OH,CF31$, and $NH3$ will be described.