Knowledge Bank

We have studied the $\Delta J$ = 2 rotationally shifted emission lines in the region of the strong absorption of molecular iodine which occurs within the 5145 {\AA} argon ion laser line. We used an etalon tuned, single frequency argon ion laser with a linewidth of 20 MHz to excite the iodine emission and recorded the spectra of the rotational lines with Fabry-Perot spectrometers having resolutions up to 70 MHz (0.0023 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$). To overcome Doppler linewidth limitations we took spectra of the emission at Small angles to the exciting beam and found the lines to have widths less than our instrumental resolution and frequencies which accurately tuned with the incident laser frequency. We recorded the emission lines for laser frequencies in the absorption line center and out into the absorption wing. Our spectra show that the intensity of the emission lines follows the absorption line profile while the frequency of the emission lines is determined by the laser frequency; the intensity is maximum at the absorption line center, falling by 10$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$ as the laser frequency is moved off the line center, while the line position maintains a constant frequency shift from the laser frequency.