Aerodynamically mixed fast-flow CO2 lasers

A supersonic nozzle in a laser tube provides three advantages: increased rate of laser gas flow, lower gas temperature due to adiabatic expansion and generation of shock waves which homogenize the plasma. Small discharge currents cause weak shock waves and the plasma is neither uniform nor stable. Large discharge currents, on the other hand, cause strong shock waves which generate a homogeneous, stable plasma and yield large gain. A maximum small-signal gain of 11.7 dB is obtained for a flow rate of 180 l/min, a mixing ratio of CO2:N2:He of 1:4.3:9.5 and a discharge current of 100 mA. The saturation parameter is proportional to the square of the gas pressure and is 2000 W/sq cm for a flow rate of 210 l/min. The drift section functions well and its length influences the gain and hence the output power because of the long relaxation time of the excited levels of the laser gas. With a suitable resonator we observed output power of 600 W/m for a discharge current of 120 mA and flow rate of 210 l/min.