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We report the performance of two new laser dyes, Pyrromethene 580 and 597, in a 10-Hz, Nd:YAG-pumped dye-laser system. These dyes demonstrate broader and more efficient tuning curves compared with those of Rhodamine 590 and 610. Pyrromethene 580 and 597 provide peak conversion efficiencies of 38% at 552 nm and 32% at 571 nm, respectively. Moreover, these new dyes provide conversion efficiencies of 31% near 572.5 nm, a wavelength used for fluorescence studies of NO. This enhanced efficiency should improve the signal-to-noise ratio in linear fluorescence [NO] measurements.

We describe a new single-laser, two-step fluorecence technique for detecting atomic hydrogen and demonstrate its application to flame measurements. This method provides the advantages of a previously demonstrated two-step method (two-photon 243-nm n = 1 → n = 2 excitation and subsequent single-photon 656-nm n = 2 → n = 3 excitation, by using two beams produced with two dye lasers) but with a much simpler experimental implementation (two-photon 243-nm n = 1 → n = 2 excitation and subsequent single-photon 486-nm n = 2 → 4 excitation, by using the fundamental and frequency-doubled beams from a single 486-nm dye laser).

Asynchronous optical sampling (ASOPS) is a pump-probe method that has strong potential for use in turbulent, high-pressure flames. We show that rapid measurement of species number density can be achieved by maintaining a constant beat frequency between the mode-locking frequencies of the pump and probe lasers. We also describe the instrumental timing parameters for ASOPS and consider the optimization of these parameters. Measurement of the nanosecond decay for electronically excited sodium in an atmospheric flame demonstrates the viability of the ASOPS technique in highly quenched flame environments.

Quenching-independent fluorescence by atomic hydrogen has been measured with photoionization controlled-loss spectroscopy (PICLS) in stoichiometric and fuel-rich premixed These H2/O2/N2 flames at a pressure of 20 Torr. These measurements are compared with conventional fluorescence measurements in the same flames. When matched in the postflame zone, the two sets of measurements diverge in the preheat zone between the burner surface and the peak of the fluorescence profiles. This divergence, caused by changes in the local quenching rate coefficient, shows the utility of PICLS for determining the kinetics of atomic hydrogen in the preheat zone.

We have measured nitric oxide (NO) concentrations in flames by using electronic-resonance-enhanced coherent anti-Stokes Raman spectroscopy (ERE-CARS). Visible pump and Stokes beams were tuned to a Q-branch vibrational Raman resonance of NO. A UV probe beam was tuned into resonance with specific rotational transitions in the (v"=1,v'=0) vibrational band in the A(2)Sigma(+)-X(2)Pi electronic transition, thus providing a substantial electronic-resonance enhancement of the resulting CARS signal. NO concentrations were measured at levels down to 50 parts in 10(6) in H(2)/air flames at atmospheric pressure. NO was also detected in heavily sooting C(2)H(2)/air flames at atmospheric pressure with minimal background interference.

We report a technique that is capable of making simultaneous two-point time-series measurements of minor-species concentrations in turbulent flames. The experimental setup, which incorporates picosecond time-resolved laser-induced fluorescence, has a spatial resolution of less than 250 microm and a temporal resolution of less than 100 micros, which spatially and temporally resolve microscales in many turbulent flows. Two-point time-series data are given for a standard turbulent nonpremixed flame at Re= 10,000, including a discussion of potential implications.

We report on a novel laser-induced fluorescence triple-integration method (LIFTIME) that is capable of making rapid, continuous fluorescence lifetime measurements by a unique photon-counting technique. The LIFTIME has been convolved with picosecond time-resolved laser-induced fluorescence, which employs a high-repetition-rate mode-locked laser, permitting the eventual monitoring of instantaneous species concentrations in turbulent flames. We verify the technique by application of the LIFTIME to two known fluorescence media, diphenyloxazole (PPO) and quinine sulfate monohydrate (QSM). PPO has a fluorescence lifetime of 1.28 ns, whereas QSM has a fluorescence lifetime that can be varied from 1.0 to 3.0 ns. From these liquid samples we demonstrate that fluorescence lifetime can currently be monitored at a sampling rate of up to 500 Hz with less than 10% uncertainty (1 sigma) .

We report a developing technique capable of making continuous time-series measurements of naturally occurring minor-species concentrations. The high repetition rate of the mode-locked laser used in this technique allows for the study of transient combustion events, such as turbulence, and their effect on minor-species concentrations. The technique is applied to make CH fluorescence time-series measurements and to calculate power spectral densities in a turbulent nonpremixed flame. To our knowledge, the reported time series represents the first such measurement for a naturally occurring minor species in a turbulent flame.

We report the first use to our knowledge of the anomalous fluorescence of pyrene to determine flame temperature. Vapor-phase pyrene was injected into fuel-rich ethylene/oxygen flames at 80 Torr. The relative laser-induced (S(2) --> S(0))/(S(1) --> S(0)) emission was monitored as a function of height above the burner and compared with the temperature profile as measured by thermocouples and sodium D-line reversal. The agreement between the ratioing technique and the flame-temperature profile demonstrates the potential of the method.

We report the first two-photon-excited hydrogen-atom fluorescence measurements in flames made to our knowledge. The n = 3 level of the H atom was excited by 205.1-nm radiation generated by Raman shifting a 224-nm beam produced by frequency mixing. Fluorescence was observed at 656.3 nm as a result of radiative decay from n = 3 to n = 2, the Balmer-alpha transition. A novel technique, photoionization-controlled loss spectroscopy, is proposed to eliminate the quenching dependence of the fluorescence signal.

A single-pulse, laser-saturated fluorescence technique has been developed for absolute OH concentration measurements with a temporal resolution of 2 nsec, a spatial resolution of less than 0.1 cu mm, and an estimated accuracy of + or - 30 percent. It has been applied in laminar, transitional, and turbulent hydrogen-air diffusion flames, providing the first reported quantitative measurements of average values, rms fluctuations, and probability-density functions of OH-radical concentration in nonpremixed flames.