This thesis describes the development of instrumentation for a high resolution 0.78 mum laser diode spectrometer operated at room temperature. Single mode GaAlAs laser diodes are used with a tunability of 0.06 nm/°C. A computer controlled temperature scanning control system, which completely removes the need for precision instrumentation amplifiers and ultra-low-temperature coefficient components featured in previous designs, was developed. This system is capable not only of generating rapid temperature scans but maintaining a set point temperature to an accuracy of +/-2 mK in a range of 11 to 36 °C. A Michelson-type infrared wavemeter of 0.01 nm precision is used for coarse frequency calibration and the water vapour spectrum is used as an absolute wavelength standard. Fine frequency calibration is done using a Fabry-Perot etalon of 0.25 cm-1 free spectral range, which is also used to monitor the mode structure of the laser and record the occurrence of a mode hop during a scan. By modulating the injection current of the laser, relatively weak, overtone spectral features of molecules can be extracted from background by means of frequency modulation spectroscopy. More than fifty lines of the nu1+3nu3(a) and the nu1+2nu2+nu3+4v40(b) bands of acetylene in the 12666-12731 cm-1 region, have been measured with the above spectrometer to a precision of 0.003 cm-1, yielding much improved band centres and upper state molecular constants as; nu0(a) = 12675.668(7) cm-1, B'(a) = 1.15158(16) cm-l and D'(a) = 2.98(83)xl0-6 cm-1; nu0(b) = 12710.913(4) cm-1, B'(b) = 1.15794(18) cm-1 and D'(b) = 5(l)xl0-6 cm-1. A two-level crossing interaction treatment has been applied to both bands, giving reasonable explanations of closely split lines within them. An -resonance treatment is further included to analyse a global perturbation in the nu1+2nu2+nu3+4nu40 band.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:488100 |
| Date | January 1993 |
| Creators | Li, Daqun |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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