Significant milestones for quantitative laser-based diagnostics of reacting flows were reached on two separate tasks: (1) the extension of laser-based diagnostics to shorter vacuum ultraviolet (vuv) wavelengths and (2) the development of amplified spontaneous emission (ASE) diagnostics for light atoms. For the first task, phase-matching was applied to produce significant increases in vuv laser intensities, producing over 5 mu J at Lyman alpha (121.6 nm) in a mixture of krypton and argon. Factors affecting the long-term stability of vuv powers were studied. The diagnostic potential of two-photon excited ASE of atomic hydrogen and oxygen was explored in a variety of low-pressure flames. Direct ASE gain measurements gave oxygen concentrations. A model of the ASE signal was developed, and a new understanding of both ASE and laser-induced fluorescence of two-photon excited atoms emerged from this model.