Techniques of Diode Laser Spectroscopy and Spectroscopic Studies of Isotopic Ozone Relevant to Stratospheric Science.

Available from UMI in association with The British Library. The operating procedures for Doppler limited diode laser spectroscopy at 10 mum, using lead salt diode lasers cooled by a liquid helium refrigerator, are described. A novel method of diode laser spectrometer operation has been developed based on temperature tuning of laser frequency. This method overcomes the two difficulties of mechanical vibration and temperature fluctuation associated with the use of helium refrigerators. The spectroscopic performance of PbSnTe diode lasers, fabricated by the Physics Department of Hull University has been evaluated. Methods to improve the limited operating lifetimes and reduce satellite mode emission have been proposed. The frequencies and absolute intensities of about 200 spectral lines in total of the oxygen 18 ozone isotopes 668, 686, 886, 868, and 888 have been obtained in the 10 μm region. Techniques were developed to produce the isotopes selectively and also in known proportions, to allow identification and intensity calibration relative to lines in the nu_3 band of ozone 666. A small (5 +/- 1%) enrichment of ozone 668 and 886 was found when ozone was prepared by silent electric discharge. The results are in agreement with an enrichment mechanism proposed by Heidenreich and Thiemens, rather than an alternative mechanism recently proposed by Valentini. The techniques developed in obtaining the ozone spectra have been applied to investigate possible mechanisms to account for a 40% + enhancement of ^ {50}O_3 which has been measured in the stratosphere. The Heidenreich and Thiemens enrichment mechanism appears to offer the most likely basis for an explanation of the stratospheric measurements. In work carried out at the National Physical Laboratory, the spectroscopic performance of 1.3 μm InGaAsP/InP lasers, and their suitability for methane monitoring was evaluated. A minimum detection limit equivalent to 250 ppm of CH_4 at a pressure of one atmosphere and over a pathlength of 200 m was demonstrated.