Knowledge Bank

Stable isolation of $CO2$ and $H2O$ rotational lines were found to be an inherent property of a concentric plasma formed with a large diameter (4.37 cm.), 3 meter longitudinal discharge tube employing a small diameter (2.54 cm.) internal grating. Certain aspects of a concentric plasma cavity will be discussed. Longitudinal mode tuning was unnecessary to preserve line isolation. Operation in the $TEM11$ mode produced simultaneous emission from several vibrational bands. Figure 1 illustrates such a spectrum. The $CO2$ laser emissions in the 8--9 micron region which appear to be new, coincide with higher order $CO2$ vibrational $bands.1$ In addition to the standard 9.4 and 10.4 micron bands, laser emission was observed from 11--15 microns. Many of these lines confirm the 11--18 micron efforts of Hartman and $Kleman.2$ The remainder are believed to be new. The 8--15 micron constraint was imposed by the available grating. A project has been undertaken to produce additional spectra over 3--30 microns with Q-switching and pulse excitation. With the very high resolution IR facilities of the AFCRL Radiometry Branch, efforts are underway to contribute to the construction of very accurate molecular energy levels for $CO2$. Similar work has been done by Benedict et al on $H2O.3$ The concentric plasma laser cavity technique has been valuable in providing a highly stable wide-band infrared wavelength reference source as well as in the study of molecular properties. The technique is being adapted in other $quarters.4$