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Title: Novel polarization phenomena and their spectroscopic application in bulk solids and films
Author: Bennett, Peter Jonathan
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 1998
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An advanced femtosecond laser micropolarimeter has been developed for transient pump-probe polarization measurements in opaque and semitransparent samples. The polarimeter has been used with femtoecond Kerr modelocked Ti:sapphire (810nm) and Cr:forsterite (1260nm) lasers, and in both reflective and transmissive configurations. A time resolution of 32fs was achieved with the Ti:sapphire laser, in a reflective configuration, and a time resolution of 90fs was achieved with the Cr:forsterite laser. In both cases a resolution to polarization azimuth rotation better than 10^-6 radians was achieved. A double pass polarimeter, based on a polarization modulation technique, has been developed for the study of nonreciprocal polarization occurring on the background of strong natural polarization rotation. A sensitivity to nonreciprocal polarization rotation better than 5 x 10^-4 radians has been achieved at several wavelengths of an argon ion laser: 514.5, 501.7, 496.5, 476.5 and 457.9 nm. The degenerate cubic optical nonlinearity in bulk gold was measured for the first time, at wavelengths of 1260nm and 810 nm, using a technique based on the pump-probe specular inverse Faraday effect. A reflected probe polarization azimuth rotation of ~1 x 10^-14 rad cm^2/W of pump power was seen in gold at 1260 nm, this corresponds to a considerable nonlinearity of |chi xxyy(3)(w,w,w,-w) - chi xyyx(3)(w,w,w,-w)| ~ 10^-9 esu (gaussian), 10^-16 m2 Volt^-2 (SI). The nonlinear response was found to be faster than 40fs at 810nm, and faster than 90fs at 1260nm. The nonlinearity is attributed predominantly to a spin-flipping mechanism. The frequency degenerate nonlinear optical response has been measured for the first time in opaque and semitransparent nickel films, of ~3-30nm thickness, at a wavelength of 810nm. Simultaneous measurements of the pump induced polarization azimuth rotation in reflective and transmissive configurations, at both the air and glass interfaces of the nickel films, indicated the importance of the surface in determining the nonlinear response. It has been established that the surface layer significantly influences the nonlinearity to a depth of about 4-5nm into the bulk. The nonlinear polarization rotation appears on the background, but is independent of, the linear polarization rotation due to the Kerr effect. From the large specular inverse Faraday effect observed, nickel films have been shown to be suitable for use in broadband femtosecond autocorrelation pulse duration measurements. A nonlinearity of liquefying gallium has been used to achieve broadband light by light modulation, at milliwatt operating power levels, with a frequency band spanning up to several hundred kilohertz, in a fibrized all-optical switch. For the first time nonreciprocity of natural polarization rotation has been seen in the optically active crystal, Bi12SiO20. A nonreciprocal component of the polarization rotation of ~2 x 10^-3 radians was observed on the background of the polarization rotation due to conventional optical activity. The nonreciprocal rotation has been attributed to the presence of the symmetric part of the nonlocality tensor Re{gamma xyz + gamma xyz} ~ 5 x 10^-12 cm (gaussian), 6 x 10^-9m (SI), at 457.9nm. [note that "w" represents l.c. omega].
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; TK Electrical engineering. Electronics Nuclear engineering Optics