A sealed high-repetition-rate TEA CO2laser

A compact atmospheric pressure CO
2
laser utilizing a double-discharge technique has been constructed and operated at repetition rates to 100 pulses/s. With the addition of small amounts of hydrogen and carbon monoxide to give a gas mixture of He:N
2
: CO
2
:CO:H
2
= 69.3:11:15:4:0.7, sealed operational lifetimes exceeding
2 \times 10^{6}
pulses have been obtained. Operating in this mode, the output energy density is about 8-9 J/l at repetition frequencies of 30-40 pulses/s for input energy densities of 60-70 J/l. The operation of the sealed laser has been studied by means of mass spectroscopic measurements of the gas mixture. It has been determined that sealed operation is possible as long as the oxygen concentration is kept below 1-2 percent. It has also been found that the addition of small amounts of H
2
and CO will keep the oxygen concentration below 2 percent by reducing the CO
2
decomposition, allowing sealed operation. The experimental results are compared to the predictions of a theoretical model in which neutral and negative-ion processes have been included. The calculations indicate that when small amounts of oxygen or water are present in the discharge the negative-ion population is significantly increased and the ratio of negative-ions to electrons
N_{n}/N_{e}
can approach values near unity. These are the conditions under which discharge arcing was found to occur. The model also predicts that the dissociation equilibrium of the CO
2
can be controlled by the addition of the above concentrations of hydrogen and CO.