Long life static gas CO2-He laser

We have obtained a lifetime ill excess of 1100 hours on one gas fill of a static gas cw CO2-He laser. The Brewster window tube, which has a 92-cm discharge length and a 10 mm i.d., produced an output power of 1.4W (within 10%) throughout this period, and showed no indication of decreasing when the test was arbitrarily terminated. From this and other lifetest data to be reported, the long life is attributed to exclusion of nitrogen, careful vacuum technique and outgassing procedure, and dc electrodes which minimize hot spots and sputtering. In all our tests addition of nitrogen to CO2and to CO2plus He caused short lifetimes and reduced output power except in the first few sconds. The partial pressure of CO2was measured by condensing it in a cold finger at 77 ° K. After 1100 hours of continuous operation, a measurement of the CO2partial pressure showed that only 15% of the CO2gas fill was undissociated. The low efficiency (1%) of this tube is due to the high absorption loss in the Irtran 2 windows, which, however, are nonhygroscopic and thus useful for lifetest data.