Steven N. Suchard

Kinetic study of N2(B3Πg, υ) quenching by laser-induced fluorescence☆

Abstract The quenching kinetics of N 2 (B 3 Π g , υ) have been determined in a low-pressure flow system in the absence of N atoms. Individual vibrational levels of the B state were populated by laser pumping (first-positive bands) of N 2 (A 3 Σ u + ) molecules. The latter were created upstream by energy transfer from Ar metastable atoms.

Effect of H2 Pressure on Pulsed H2+F2 Laser. Experiment and Theory

Stimulated emission predictions and measurements for an H2+F2 laser are compared for H2 pressures from threshold to stoichiometric, a range of several orders of magnitude. Slowly flowing, helium‐diluted, 50 torr mixtures are initiated photolytically. Two dilution ratios and two output couplers are considered, and good agreement is found for time‐to‐threshold and pulse duration vs H2 pressure. Spiking, relaxation oscillations, and possibly mode beating, features not modeled, are observable in some pulses; however, predicted intensity vs time generally agrees in pulse shape with laser output. Observed and predicted peak intensities nearly match for low H2 pressure, and the predicted increase of peak intensity with low H2 is followed fairly well. For H2 in the vicinity of one‐tenth stoichiometric, the peak intensity data show an abrupt leveling off, while the calculations predict a continuing increase. This disagreement most probably cannot be attributed to uncertainties in the kinetic model. All rate modifi...

Fast‐discharge‐initiated KrF laser

By means of fast‐discharge circuitry, intense laser emission was observed from the XeF molecule at 351, 353, and 349 nm in a gas mixture of He, Xe, and NF3. The over‐all electrical efficiency based on the energy deposited in the gas was 1.2%; the ’’wall‐plug’’ efficiency was 0.2%. An output energy of 1 mJ was measured from a laser pulse 40 nsec in duration, yielding a peak power of 25 kW. A simple model is proposed to estimate the laser performance.

Quasi‐cw laser emission from the second positive band of nitrogen

Experimental results are presented for the observation of a second positive nitrogen laser that has a pulse length much longer than the radiative lifetime of the upper laser level. Preliminary measurements of the temporal behavior of this laser indicate that it was operating in a quasi‐continuous‐wave manner and, in addition, the laser output was extremely sensitive to the alignment of the optical cavity placed around the discharge tube.

Time-Resolved Spectroscopy of a Flash Initiated H2-F2 Laser

The time‐dependent output spectrum of a helium‐diluted H2–F2 chain‐reaction chemical laser has been observed. Reaction of a 50‐Torr mixture with mole ratio H2 : F2 : He = 1 : 1 : 60 was initiated by flash photolysis of the F2. Strong lasing was found from P‐branch vibration‐rotation transitions of the v = 1 → 0, 2 → 1, 3 → 2, and 4 → 3 bands of HF. Within some bands, the time sequence of transitions suggests non‐Boltzmann distributions of rotational states. No lasing from vibrational levels higher than 4 could be detected.

Potential electronic transition chemical laser: parametric evaluation

Through the utilization of a generalized computer code that calculates the minimum reactive branching ratio required for a species to display optical gain, a parametric study was performed to ascertain which properties of the electronic potential curves of a heteronuclear diatomic molecule have the greatest effect on the suitability of that molecule as a potential electronic transition laser. The results of this study demonstrate that diatomic systems separate into different classes when the question of the minimum required reactive branching ratio is confronted. This separation of molecular systems was translated through the use of compiled molecular constants into a determination of which vibrational-level distribution class is most favorable for specific heteronuclear diatomic molecules to display optical gain; potential laser candidates were pointed out. In addition, a generalized gain equation for electronic transitions heteronuclear diatomic molecules that takes into account both rotational and vibrati nal partitioning was derived.

Lasing from the upper vibrational levels of a flash‐initiated H2–F2 laser

Laser action has been observed from the P‐branch vibration‐rotation bands of the HF molecule from v = 6→5 to v = 1→0 transitions. In addition, the time‐resolved spectral behavior of this He‐diluted H2–F2 chain reaction chemical laser has been recorded. The HF* lasing molecules were produced by the reaction of a 50‐Torr gaseous mixture with mole ratio H2/F2/He=0.5/1/40 initiated by flash photolysis. In contrast to earlier results, strong lasing was found on the v = 6→5 and 5→4 transitions of the HF molecule. Within some of the bands from which lasing was observed, the time sequencing of transitions suggests non‐Boltzmann distributions of the rotational states.

Behavior of the first and second positive emission in the N 2 /SF 6 laser

Experimental results for the behavior of the emission of the discharge-excited first- and second-positive bands of N 2 and flow-tube measurements for the deactivation of the A^{3}\Sigma\min{u}\max{+} and B^{3}\Pi_{g} levels of N 2 by SF 6 are presented. The results of both these experiments are used to explain the operating mechanisms of the N 2 /SF 6 laser.

Efficient pulsed chemical laser

Output pulse observations are presented for a helium‐diluted CO2 laser pumped by VV (vibration‐vibration) energy transfer from vibrationally excited DF produced by the D2–F2 chain reaction. Flash photolysis of the F2 served to initiate the reaction. A 290‐cm3 reaction chamber containing a 0.5‐atm mixture with mole ratio D2:F2:CO2:He = 0.33:1:8:10 gave a single‐pulse output energy of 2.8 J. Relative to the amount of D2 present in the reaction chamber, this corresponds to a chemical efficiency greater than 5%.

Fluorine Pressure Change Monitor for a Reacting System.

Recent experimental results on the performance of a pulsed HF chemical laser have indicated that the presence of HF in the chemical reactants prior to laser initiation degrades the laser performance. In order to monitor the amount of HF produced when the chemical reactants are mixed, a device has been developed that measures the change in concentration of one of the reactants. This device, which relies on the absorption of light by molecular F2, has been shown to have an accuracy of better than 5% in the measurement of the F2 pressure.