Munson A. Kwok

Sensitive measurement of photon lifetime and true reflectances in an optical cavity by a phase-shift method

A simplified method for measuring the effective photon lifetime in an optical resonator was developed. The technique requires the passage of a modulated cw laser beam through the resonator and the measurement of the resultant shift in the phase of the transmitted intensity. The method not only permits a quick and precise measurement of the mirror reflectances, but also permits these measurements to be in situ. Such an on-the-spot evaluation capability should be extremely useful in applications ranging from the investigation of new laser systems to the development of improved optical coatings. The method is also sensitive to the effects of absorption, scattering, and transmission from elements in the cavity. Cavity losses <100 ppm were detected.

ISOTOPE SEPARATION WITH THE cw HYDROGEN FLUORIDE LASER

A cw hydrogen fluoride laser has been used successfully to separate deuterium from hydrogen by specific photocatalysis of the reaction of methanol with bromine. The strong absorption of H/sub 3/COH was demonstrated for the HF laser lines P1(5), P1(6), and P1(7). No absorption of the HF beam by deutero-methanol was observed. Excitation of H/sub 2/COH by the absorbed beam increased the rate of H/sub 3/COH removal by reaction with bromine. Irradiation of a 1:1 H/sub 3/COH:D/sub 3/COD gas mixture in the presence of bromine for a period of 1 min with the 90-W cw hydrogen fluoride laser beam produced isotope enrichment to greater than 95 percent D/sub 3/COD.

Flow‐tube studies of vibrational energy transfer in HF(v)+HF, DF(v)+HF, and DF(v)+D2 systems

A medium‐pressure (1 Torr), large‐diameter (10 cm) flow tube has been used to measure rate coefficients at 298 °K for (a) total relaxation (sum of vibrational–vibrational and vibrational–rotational, translational processes) of HF(v=1, 2, 3, 4, and 5) by HF, (b) relaxation of DF(1, 2, 3, and 4) by HF, and (c) over‐all relaxation of DF(v=1, 2, 3, and 4) by D2. The chemically produced vibrationally excited HF or DF species have been studied by monitoring their vibrational–rotational emission in a fast‐flow system. The rate coefficient for the relaxation of HF(1) by HF is 5.3×104 sec−1⋅Torr−1. The measured rate coefficients for the deexcitation of HF(v=2, 3, 4, and 5) by HF are 5.3×105, 8.5×105, 8.8×105, and 2.8×105 sec−1⋅Torr−1, respectively. The rate coefficients for the vibrational–rotational, translational deexcitation from the upper vibrational levels of DF(v) by HF are found to have a nonlinear vibrational dependence. The rate coefficient for the relaxation of DF(v=1) by D2 is 1.35×104 sec−1⋅Torr−1.

COMPARISON OF HF AND DF CONTINUOUS CHEMICAL LASERS: II. SPECTROSCOPY

Continuous laser action has been observed on several HF and DF vibrational‐rotational transitions. The HF lases between 2.6 and 2.9μ and DF lases between 3.6 and 4.1μ. The lines are identified and the relative intensities are shown.

Flow tube studies of the deactivation of HF(v) by selected polyatomic molecules

A large diameter, medium pressure flow tube has been used to study deactivation processes by selected polyatomic molecules potentially relevant in chemical laser systems. Effective vibrational deactivation rate constants for HF(v = 1,2,3) relaxed by H2S, CO2, N2O, CH4, CF4, and SF6 have been determined. Rate constants for chaperones H2S, CO2, and CH4 are found to be about 102−103 times larger than for the CF4 and SF6. The fast rates are order 1012 cm3/mol−1·sec−1. The N2O rates are intermediate. The rates for a given chaperone increase with ascending v. The agreement with results for HF(1) + M reported from laser‐induced fluorescence experiments is generally good. The role of HF rotational energy in absorbing a vibrational energy defect is examined. An empirical correlation with adjusted vibrational energy defect is suggested.

Temperature dependence of vibrational relaxation from the upper vibrational levels of HF and DF

A kinetic model of infrared laser‐induced fluorescence experiments has been used to simulate quenching coefficients between 300 and 2400 K for the vibrational relaxation of HF(v1) and DF(v1) by HF(v2=0) and DF(v2=0). This rotational nonequilibrium model is based on the predicted energy‐transfer mechanisms in hydrogen–fluoride and deuterium–fluoride systems reported earlier by Wilkins. The deactivation rates for the V→R processes for HF(v1)+HF(v2=0) and their isotopic analogs are predicted to scale as vn with n varying from 2.3 to 1.6 as v varies from 2 to 6. These quenching coefficients for V→R processes from the upper vibrational levels are predicted to have a temperature dependence very similar to that for V→R relaxation from the v=1 level. The results are discussed in relation to V→V energy transfer and V→R intramolecular energy conversion.

Flow tube measurements of H + HF(V) deactivation rates

Abstract : A medium-pressure flow tube is used to determine the rate constants for vibrational deactivation of HF(v = 1, 2, 3) by H-atoms by monitoring the HF vibration-rotation emission. The deactivation of HF(v) by H-atoms is found to be a very efficient energy-transfer process. The experimental results are compared with available theoretical data of Wilkins.

High resolution absorption spectroscopy of NO2

Abstract The absorption cross-section of NO 2 has been measured above the 3979 predissociation limit in the region of 3920 and 3950 and in the discretely structured areas around 4112 and 4140 . Spectra were taken in a dual-beam arrangement using a tunable, pulsed dye laser with 0.05 bandwidth (FWHM). This represents an improvement of at least a factor of three over the resolution employed in previous studies. Below 3979 , the spectra are continous with occasional diffuse rotational lines superimposed. The spectra taken above 4100 reveal a wealth of structural complexity. We report here absolute cross-sections taken at 300 . The work above 4100 was also performed at 250 . Only slight variations in the measured cross-sections are observed between these two temperatures.

Temperature dependence of HF(v1=1)+HF(v2=0) vibrational relaxation

A kinetics model of infrared laser‐induced fluorescence experiments has been used to simulate the experimental quenching rate coefficients reported between 300 and 4000 K for the vibrational relaxation of HF(v1=1) by HF. This rotational nonequilibrium model is based on the predicted energy‐transfer mechanisms in hydrogen fluoride systems reported in a trajectory study by Wilkins. This model includes v→R, R→v, R→ (R′, T′), and (R′, T′) →R energy‐transfer processes. A key process is vibrational‐to‐rotational intramolecular energy transfer in which HF(v1=1,J1) terminates on high J′ 1 states ofv′1=0. The calculated temperature‐ dependent quenching rate coefficient for self relaxation of HF(v1=1) at temperatures between 300 and 2000 K is dependent on v→R andR→v energy‐transfer processes, and beyond 2000 K only on v→R processes. The temperature dependence observed for HF(v1=1) vibrational relaxation by HF(v2=0) is explained by this model. For the high roational states in the v′ 1=0 manifold, this model predicts...

Scale‐up of NF(a1Δ) produced by the H+NF2 system in a subsonic cw laser device

A peak density of the electronically excited free‐radical species NF(a1Δ) of 2.4×10−9 mol cm3 has been chemically produced in a subsonic laser device. This high concentration confirms previous analyses and predictions of the chemical system. This is a concentration scale‐up of 104 from previous flow‐tube results.