Knowledge Bank

The $aqQ7(8)$ transition of the $\nu 2$-band of $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}NH3$ is coincident with the $N2O$ P(13) laser line within its Doppler width. Observations of a clear infrared-microwave double resonance signal and a two-photon Lamb-dip were made a few years $ago.1.2$ we observed, in addition to these signals, some higher-order infrared-infrared double resonance effects which are a result of an infrared-microwave two-photon process together with a single-photon or a three-photon infrared process. The experiment was performed with an X-band waveguide cell placed either inside or outside the laser cavity. While the signals that were involved with the infrared three-photon process were observable only with an intra-cavity cell, the two-photon Lamb-dip and the infrared and infrared-microwave two-photon double resonance effects were clearly observed with both experimental arrangements. The lineshapes and widths were examined at various field intensities and sample pressures and will be described.