Knowledge Bank

Results are presented of Stark-tuned Lamb-dip measurements in the $6\mu$m $\nu 4$ and $2\nu 2$ bands of $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}NH3$ obtained using a co laser with an intracavity Stark cell. Some 230 lines form the isotopes $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}C16O,13C16O,12C18O$, and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C18O$ were investigated with fields up to 30 KV/cm. Sixty-four coincidences with Stark-tuned $NH3$ lines, involving several hundred Lamb dips, were assiqned and analyzed. The positions of these lines relative to the CO laser lines are reported with a typical accuracy of 5-20 MHz. Model calculations of Lamb-dip spectra are also given that include power and pressure broadening and the collisionally transferred resonances. These are directly compared with observed spectra, form which we deduce values for the pressure broadening coefficients and the collisional transfer efficiency. Nuclear hyperfine structure is resolved on several lines, and form fitting one of these we obtain the value $eqQ=-4.83\pm 0.30$ MHZ for the nuclear quadrupole coupling constant in the $s2\nu 2(J=10,K=9)$ state. We see numerous examples of weak ``forbidden"" transitions $\Delta MJ=O,\pm 2$, arising form the nuclear quadrupole coupling. Double resonance experiments are also described in which a $\infty$ laser pumps a $6\mu m\nu 4$ transition while a tunable diode laser probes a $10\mu m\nu 2$ transition having a common lower level. Four different combinations of pump-probe transitions are studied. The Co loser is Lamb-dip stabilized on the pump transitions, which are tuned into coincidence with it using the intracavity Stark cell. The pump an probe beams overlap collinearly in the Stark cell. The double resonance signals appear as narrow transmission peaks on the diode laser scans. The double resonance signals appear as narrow transmission peaks on the diode laser scans. The narrowest observed widths are $\cong$ 3 MHz (FWHM), a large portion of which is due to unresolved hyperfine structure. An analysis of the various broadoing mechanisms indicates that the diode laser contributes less than 1 MHZ to the width. Resonances due to velocity-preserving but state-changing collisions are seen. Asymmotries between co- and counter-propagating linewidths are shown to arise form a combination of field inhomogeneity and coherent narrowing effects. The data are recorded using a computer-aided, rapid-scan, digital signal averaging technique.