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Title: High resolution spectroscopy using tunable diode lasers
Author: Setio Utomo, A. B.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1994
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It has been demonstrated in this work that commercial hollow cathode discharge lamps can be used for optogalvanic, absorption, fluorescence and polarisation absorption techniques by sending the beams in counter propagating and perpendicular direction to the cylinder axis of the discharge lamp, in-between its anode and cathode. Experiments have been performed using a number of single mode diode lasers to investigate selected lines of argon (~772 nm), rubidium (~780 nm) and lithium (~670 nm). To control the hollow cathode discharge lamp, a special, low-noise DC power supply was built in-house. It is able to produce output voltages of up to 400 Volts at up to 50 mA current; the current is stabilised by an active current sink. The unit also incorporated an AC coupled low-noise amplifier to detect the optogalvanic signal when excitation resonance takes place in the discharge lamp. In optogalvanic (OG) spectroscopy, transitions in rubidium, lithium and argon were investigated. In the spectrum of rubidium, the intensities of the D_2-line components roughly mirror the isotopic abundances (72.15% for ^85Rb nd 27.85% for ^87Rb) and some of the hyperfine structure and isotope shifts are resolved. Only the fine structure splitting between D_1 and D_2 of the two isotopes ^6Li and ^7Li (isotope abundances of 7.4% and 92.6% respectively) are well resolved by our diode laser. The line structure shows a three-component feature; two of the components are rather strong while the third (at the longest wavelength; 2^2S_1/2 - 2^2P_1/2 transition) is very weak which is hardly detectable in the spectrum. This third, weak component due to ^6Li is often ignored in high-resolution spectroscopy. The hfs splitting of both the ground and the excited state are smaller than the Doppler width and thus are not resolved. In the spectroscopic investigation of argon lines parametric studies of the tuning behaviour of laser diodes have been performed. In addition to the well known mode hops during temperature tuning also relaxation oscillation side-bands to individual modes have been detected. In absorption spectroscopy of the three elements the spectra not only reveal the spectroscopic structure, but information on transition probabilities and particle number densities can be deduced as well.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available