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An experimental study of subsonic laser absorption waves arising from the interaction of 10.6-μm radiation with metal and insulator target materials is described. A shock-tube-driven gas-dynamic laser operating up to 400 kW for 4 msec was used as the radiation source. Instrumentation included streak photography to determine wave speed, holographic interferometry to determine the gas density field, time-integrated visible spectroscopy to determine the principal radiating species, and CO2 laser attenuation measurements to determine the plasma absorption coefficient. The results reported here emphasize the characteristics of waves in free and clean air, far from the influence of the target. The measured wave speeds in air at 1 atm pressure ranged from Mach 0.05 to 0.2 for CO2 laser intensities ranging from 1×105 to 5×105 W/cm2. The wave speeds were also found to depend on the laser beam diameter. The spectral emission and CO2 laser absorption measurements showed that the air plasma reaches a temperature of 15 000–20 000°K and is essentially fully ionized. From an analysis of the results, it is concluded that radiation transport in the plasma plays a dominant role as a wave propagation mechanism, and that radial flow ahead of and within the wave is a dominant feature of the wave structure.

Detailed spatial and time-dependent measurements of the electrical parameters and the gas properties have been made on a high-average-power quasisteady supersonic cw carbon monoxide electron-beam-stabilized electric-discharge laser. The electrical and optical measurements show that there are major changes in the current-density distribution and in the supersonic flow field due to the high electric-discharge power input to the gas. A multipin resistor-ballasted electrode has been used to make the current density much more uniform, resulting in a factor-of-2 increase in electrical energy input and in laser power output. Small-signal gain measurements were made on the J=7 to J=13 rotational lines of the V=7 to V=6 CO vibrational transition at various locations in the electrical discharge. The measured rotational temperature showed that only 12% of the discharge power went into gas heating in the supersonic free-stream region. The measured small-signal gain was as high as 0.08 cm−1, the maximum electrical energy density input was 430 J/l amagat, and the maximum laser power density extracted was 120 kW/l.

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