Novel Nonlinear Laser Diagnostic Techniques

Abstract

Abstract : Research on novel laser-based diagnostic techniques in two areas is described: (1) extension of laser-based diagnostics to shorter wavelengths for two-photon detection of atomic ions and other detection techniques requiring high powers in the vuv and (2) investigation of quantitative concentration, temperature, and velocity measurements using two-photon-excited amplified spontaneous emission (ASE) of atomic oxygen and hydrogen. For the first task, a broadly tunable high power vuv source based on two-photon-resonant difference frequency mixing in hydrogen and krypton gas was developed. Up to 65 mJ at 133 nm was generated and wavelengths as short as 122 nm were produced. This radiation was applied to multiphoton spectroscopy at vuv wavelengths below 150 nm, including two-photon-excited fluorescence in neon at 133 nm. Research on Task 2 included demonstration measurements of the bandwidth of ASE signals from both oxygen and hydrogen atoms in low-pressure flames. A model of the ASE signal shows gas temperature determination from ASE bandwidth measurements is possible. Gain on a cw diode probe laser from two-photon-excited oxygen atoms has been demonstrated in low-pressure flames; from such direct gain measurements, quantitative atom concentration measurements are feasible.