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Title: Infrared spectroscopy of multi-quantum well microcavities
Author: Murphy, Francis John
ISNI:       0000 0004 5349 3603
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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Two projects are presented in this thesis. The first project is an investigation into linewidth-narrowing phenomena of intersubband cavity polaritons (ICPs) in a microcavity/multi-quantum well sample through angle-resolved laser spectroscopy. Strong coupling of the vacuum field of the microcavity, and the intersubband transition (ISBT) of the multi-quantum well led to vacuum Rabi splitting of 12.4 meV of the ICP modes at room temperature in the absorbance spectra. The linewidths of the ICPs were found to be substantially narrowed (4.2 meV, at room temperature) at the anticrossing point, narrower than the bare ISBT and empty microcavity linewidths at room temperature (6.2 and 6 meV, respectively, at room temperature), and narrower than existing theory predicted. The same effect was observed at cryogenic temperatures. Narrowing was explained by the light effective mass of the ICP, rendering the ICP unaffected by interface roughness scattering of the multi-quantum well. The measurement of the narrow linewidths was made possible by the superior angular resolution of laser spectroscopy compared to previously-used thermal light sources. The second project consisted of the development of a Q switched Er 3+ ,Cr 3+ :YSGG laser, of 3 μm wavelength, with 76 mJ fundamental mode pulses in free-running mode. Q switching of the laser was investigated in order to produce short (<400 ns) laser pulses, using two 'slow' Q switch methods. The first, a rotating mirror Q switch, was found to produce pulses of ~10 mJ, with an optimum mirror rotation rate of 300 rotations per second. The second Q switch method, a 'polygon chopper Q switch' produced single pulses of energy ~4 mJ, using a rotating polygon as an optical chopper. From this Q switch, it was deduced that the longest Q switching time possible for Er 3+ ,Cr 3+ :YSGG, with any method of Q switching, was ~30 μs for single pulse operation, and ~80 μs for multiple pulses.
Supervisor: Phillips, Chris C. Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available