Abstract

The results of a theoretical study carried out to explore the possibility of obtaining quantitative information about density fluctuations in a turbulent air flow is presented. The specific technique considered for analysis is a new three-level gain measurement scheme which consists of using a high-power pulse laser to saturate one transition of a molecule and then measuring gain on a coupled transition of the same molecule with a probe laser. It is shown that the most promising of all the three-level schemes considered in CO₂ and H₂O is the one which involves pumping the R(12) line of the 021↔000 band in CO₂ with an HF laser and measuring the gain on the P(16) line of the 021↔020 band with a CW diode laser. Our study shows that in the case of random and isotropic turbulent flow fields, the energy and power spectrum can be obtained with the use of commercially available lasers. The possibility of conducting a simulation experiment in the laboratory is discussed, and the use of this diagnostic to measure turbulent density fluctuations behind an airplane is explored.