Accurate gas diagnostics for sealed-off CO/sub 2/ lasers using near-infrared DFB semiconductor lasers

The selective spectroscopic detection of CO/sub 2/ and H/sub 2/O in the gas mixture of a 400-W sealed-off CO/sub 2/ slab laser is reported. The detection is based on the acquisition of absorption Voigt profiles of two vibrational overtone transitions of CO/sub 2/ and H/sub 2/O, obtained using two InGaAsP distributed feedback (DFB) semiconductor lasers. This spectroscopic method enables a direct absolute measurement of the temporal evolution for the concentrations inside the laser active volume. Monitoring takes place during laser operation without gas extraction. The experiments carried out on CO/sub 2/ and H/sub 2/O abundances confirm the paramount importance of wall desorbance phenomena in all-metal radio frequency (RF) excited lasers.