Anomalous gain in an isotopically mixed CO/sub 2/ laser and application to absolute wavelength calibration

Measurements are reported on a grating-tuned CO/sub 2/ laser, containing an isotopic mixture of /sup 16/O/sup 12/C/sup 16/O, /sup 16/O/sup 12/C/sup 18/O, and /sup 18/O/sup 12/C/sup 18/O. The P/sub 6/ and R/sub 14/ lines of /sup 16/O/sup 12/C/sup 16/O were found to have anomalously high intensities. These anomalies are produced by the near coincidence of the transition frequencies in two distinct isotopes, permitting them to act as a single indistinguishable population. These two lines can be used to identify the rotational quantum numbers in the P and R branch spectra, thereby permitting absolute wavelength calibration to be achieved.<
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