Engineering topics
Publications and source records attributed to Mcdermid, I. S..
A time-resolved study of the optogalvanic effect in a pure iodine discharge is reported for pulsed dye laser irradiation at 585 nm. By varying both the spatial location and pulse energy of the laser probe, several contributions to the time evolution of the optogalvanic signal are identified and their origin discussed.
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The capabilities of excimer lasers for remote sensing applications are illustrated in a discussion of the development of a compact tunable XeCl excimer laser for the detection of atmospheric OH radicals. Following a brief review of the operating principles and advantages of excimer lasers, measurements of the wavelength dependence of the net small signal gain coefficient of a discharge excited XeCl laser are presented which demonstrate the overlap of several absorption lines of the A-X(0,0) transition of OH near 308 nm with the wavelengths of the XeCl laser. A range of continuous narrow bandwidth tunability of from 307.6 to 308.4 nm with only a 30 percent variation in output is reported for an XeCl laser used as a double-pass amplifier for a frequency-doubled dye laser, and measurements demonstrating the detection of laser-induced fluorescence from OH in a methane-oxygen flame are also noted. The design of an oscillator-amplifier excimer system comprising a corona-preionized, transverse-discharge oscillator and amplifier is then presented. Output energies of 12-15 mJ have been achieved in the regions where injection locking was established, with energies of 8-10 mJ elsewhere.
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A narrow-bandwidth pulsed dye laser was used to excite OH X 2Pi i radicals to the A 2Sigma(+) state by pumping in the (0, 0) vibrational band around 308 nm. The radiative lifetimes of specific (K-prime, J-prime) rotational levels in v-prime = 0 were measured at low pressures (not greater than 1 mtorr), which yielded a mean lifetime of 0.71 + or - 0.009 microsec (2 sigma). Electronic quenching rate constants for N2, O2, H2O, and H2 were measured for a range of initially excited rotational levels. A strong dependence of this rate constant on the initially excited rotational level was found for N2, and less markedly for O2, with the rate constant tending to increase for the lowest rotational levels K-prime not greater than 3. The implications of these results for the laser-induced fluorescence detection of atmospheric OH are discussed.
A holographic grating at grazing angle of incidence was used to achieve tunable, narrow bandwidth (0.005 nm) operation of a XeCl oscillator for injection locking of a ring amplifier. The amplifier's narrow bandwidth output energy was constant and equal to the untuned, broadband output (approximately 15 mJ) in regions where injection locking was achieved. Scanning was provided by use of a stepping motor-driven differential micrometer on the tuning mirror. This system was used to produce a laser excitation spectrum of hydroxyl radicals (OH) in a flame.