Photoacoustic Detection of Atmospheric Absorptions Using a cw Ring Dye-Laser

The intracavity dye-laser photoacoustic-detection technique is extremely sensitive permitting detection of weak absorptions in benzene1 with cross sections as low as 10−27 cm2 at 9.3 kpa (70 Torr) of vapor pressure (absorption coefficient α ~ 10−9 cm−1). The high sensitivity of this technique makes it useful for detecting weak atmospheric absorptions in the near-IR and visible regions. Atmospheric absorption characteristics of high- and low-energy lasers (for example the chemical iodine laser at 1.315 μm and the blue/green laser at 496 nm) are required for selecting and optimizing a particular laser for communications and military applications requiring a long pathlength in the atmosphere. The photoacoustic detection technique is advantageous because it directly measures only the absorption loss which is the principal source of thermal blooming in high-energy laser propagation. Moreover, the small size of photoacoustic cells makes them ideal for quantitative studies of collisional broadening, lineshape, temperature dependence, and the simulation of real-time airborne variations. Similar studies are tedious and time-consuming tasks with large-volume multipass cells.