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Title: Narrow bandwidth tunable diode laser system for applications in spectroscopy and interferometry
Author: Kudayair, A. A.-S.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1995
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All electronics necessary for stable and versatile operation of the laser system were designed and built during the course of this research work. The injection current driver and the temperature controller for the diode laser compare favourably with standard commercial devices of considerably higher cost, exhibiting reproducibility in the laser's output centre frequency of < 1 MHz and ~ 4 MHz/mK respectively. To enable realisation of stability of that centre frequency a simple but very effective locking circuit was built based largely on digital electronics. Exploiting the modulation of an atomic transition frequency via a magnetic field (Zeeman modulation) one of the diode lasers was successfully locked to an absorption feature of the Rb D2-line, without change in emission frequency of the laser, over long periods of up to a day. Narrow linewidths for Sub-Doppler spectroscopy, for example, were realised using a simple external cavity, based on two GRINRODs. Careful alignment of the cavity allowed us to achieve single-mode operation with the linewidth reduced from typically 20-50 MHz to below 1 MHz, without introducing side-modes from the external cavity. The linewidth was measured indirectly in a long-arm Michelson set-up, limited only by the space available for the interferometer (in our case a folded set-up of 150 m length). The still extremely good visibility of fringes makes this a demonstration of one possible application of our laser to long-range interferometry. Two spectroscopic applications were demonstrated in this work, namely optogalvanic (OG) and absorption spectroscopies. OG signals were obtained in standard hollow-cathode spectral lamps, for a number of transitions in Ar, K and Rb. Mostly those measurements were taken in the Doppler-limited regime, thus without the need for the external cavity. Both intensity modulation (chopping of the laser beam) and frequency modulation (varying the emission frequency of the laser) were employed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available