Circumstellar disks are critical structures in the star and planet formation processes, as they provide a conduit to channel material onto the central object and supply a reservoir of dust and gas to form planets. This thesis focuses on the far-infrared, and sub-millimeter observations of circumstellar disks at two key evolutionary phases; pri- mordial proto-planetary disks, and evolved debris disks – remnants of a system that has undergone a degree of planet formation. Four individual studies of circumstellar disks are presented in this thesis. The results of a 97% complete census of far-infrared emission measured with the Herschel Space Observatory, targeting stars of spectral types M4 and later, in the Taurus molecular cloud are presented. This census is the first large-scale survey sensitive to emission across the stellar and sub-stellar boundary. Results from an initial test grid of model spectral energy distributions, generated with the radiative transfer code MCFOST, show that 73% of the observed Class II population are constrained by canonical disks that are viewed from face-on to edge-on inclinations. Sub-millimeter observations with the Caltech Sub-millimeter Observatory are presented for an association of young T-Tauri stars in the Aquila star-forming region. The results of disk frequency and disk mass of this complete census are investigated in this extremely low stellar density environment. A sub-millimeter investigation for two populations of candidate debris disk; warm and cold excess disks is presented. None of the candidate disks were detected in the sub-millimeter despite upper-limits below that expected, based on blackbody model fits to excesses at shorter wavelengths. Several scenarios are investigated in order to identify the null detection rate, such as stellar multiplicity and background-source contamination. Finally, a partially resolved sub-millimeter map of the debris disk around the HR 8799 multiple planetary system is presented. The planet formation history of the system is investigated through the witnessed morphology of the emission.

<p> The optical absorption in manganese fluoride has been studied in the range of 30 to 300 cm^-1 with emphasis placed on the possible multiple magnon absorptions (other than two-magnon) and an induced single magnon absorption. It is shown that theoretically one can expect four-magnon processes by expanding the Heisenberg spin hamiltonian to higher orders in the creation and annihilation operators introduced by the Holstein-Primakoff transformation. However, neither an induced one magnon nor four magnon process was observed. The absorptions which were seen in the spectra were attributed to phonon processes.</p> / Thesis / Master of Science (MSc)

<p> A technique has been developed for constructing low temperature germanium bolometers for use as detectors in the far infrared. Their performance has been evaluated both by measuring their responsivity and noise and comparing these with the theoretical values and also by using the bolometer in conjunction with a far infrared spectrophotometer to obtain spectra showing the theoretical resolution of 0.11 cm^-1 at 55 cm^-1 expected for this instrument.</p> / Thesis / Master of Science (MSc)

The consumption of spiced food is steadily increasing, subsequently leading to increased incidence of spice-related food illnesses. Many outbreaks can be traced to human pathogens that can survive in low moisture content of spices, prompting development of additional inactivation treatments that reduce bacterial pathogens while maintaining spice quality. Spices are currently treated by fumigation with ethylene oxide, pasteurization with ionizing radiation, or steam treatment. However, these treatments exhibit flaws pertaining to consumer preference, regulatory issues, and quality degradation. In this study, two novel treatments were evaluated for reduction of Salmonella enterica Tennessee: far infrared radiation (FIR), a short time â " high temperature treatment, and pasteurization with ethanol vapor (EV). Both treatments were effective in reducing levels of Salmonella Tennessee between 3-5 logs. FIR treatment showed increased efficacy at longer treatment times with a maximum reduction of 5 log CFU/g in paprika at 24s. EV reduced Salmonella Tennessee by 3 log CFU/g within 120s when applied to inoculated paprika and black pepper without detrimentally affecting spice quality. However, the samples receiving FIR treatments suffered reductions in volatile content and color changes to the spices. High levels (up to 1% w/w) of residual ethanol were also detected on samples treated for 300s. Concluding, both treatment show similar results when comparing efficacy; however, based on the magnitude of change in volatile content associated with FIR being significantly greater than those samples receiving EV, FIR treatment requires additional research before recommending for use with dried, ground paprika, black pepper, or sage. / Master of Science

Protoplanetary discs set the initial conditions for planet formation. By combining observations with detailed modelling, it is possible to constrain the physics and chemistry in such discs. I have used the detailed thermo-chemical disc model ProDiMo to explore the characteristics of the gas in protoplanetary discs, particularly in Herbig Ae objects. I have assessed the ability of various observational data to trace the disc properties. This has involved a number of different approaches. Firstly I compute a series of disc models with increasing mass, in order to test the diagnostic powers of various emission lines, in particular as gas mass tracers. This approach is then expanded to a large multiparameter grid of ~ 10 5 disc models. I have helped to develop a tool for analysing and plotting the huge quantity of data presented by such a model grid. Following this approach I move on to a detailed study of the Herbig Ae star HD 163296, attempting to fit the large wealth of available observations simultaneously. These include new Herschel observations of the far-infrared emission lines, as well as interferometric CO observations and a large number of continuum data. This study addresses the topical issues of the disc gas/dust ratio, and the treatment of the disc outer edge. It explores the effects of dust settling, UV variability and stellar X-ray emission on the disc chemistry and line emission. There is possible evidence for gas-depletion in the disc of HD 163296, with the line emission enhanced by dust settling, which would indicate a later evolutionary stage for this disc than suggested by other studies. Finally, I work to improve the treatment of the gas heating/cooling balance in ProDiMo, by introducing a non-LTE treatment of the atomic hydrogen line transitions and bound-free continuum transitions. I explore the effects of this on the disc chemical and thermal structure, and assess its impact in terms of the observable quantities.

This thesis describes an experimental study of high intensity, pulsed, optically pumped, far-infrared (FIR) lasers. The work was motivated by the need for a radiation source for the measurement of the ion temperature in magnetically confined, high temperature plasmas (e.g. tokamak plasmas), using Thomson scattering. Constraints imposed by the plasma parameters, the scattering geometry and available detector sensitivities lead to the requirement of a radiation source wavelength between 30μm and 1mm and a source power . 1 MW in a bandwidth 60 MHz. Results are presented for a 496μm, 500 watt, methyl fluoride (CH₃F) cavity laser, with a bandwidth of and < 30MHz, which was optically pumped by a 9.55μm CO₂ laser. Results are also presented for an optically excited mirrorless, super-radiant, CH₃F laser, which generated over 0.6MW of FIR radiation within a bandwidth of about 300MHz. The performance of this laser has also been simulated by a computer model, which allows the optimum operating parameters to be predicted. An assembly constructed on the principle of the injection laser, in which low power narrow-band oscillator radiation is used to control the output of a super-radiant system, has been used to generate 250 kW of 496 andmu;m radiation, with a bandwidth of < 60 MHz. Investigations of the FIR output from heavy water vapour (D₂O) in a super-radiant laser assembly, optically excited by several different CO₂ laser wavelengths, have resulted in the generation of 60 ns (FWHM) pulses of FIR radiation with average powers of 1.3, 9.2 and 15.8MW, at wavelengths of 385, 119 and 66μm, respectively. All these lasers were found to have a higher CO₂ to FIR photon conversion efficiency than the 496μm CH₃F laser. In addition, the energy level spacing in D₂O is such that the molecule can generate narrow bandwidth radiation more readily than the CH₃F molecule. From this work it is concluded that an injection laser assembly, similar to that used with CH₃F, but containing D₂O vapour, optically pumped by a 9.26μm CO₂ laser and generating several megawatts of 385μm radiation, would satisfy the source requirements mentioned above.

This report describes an experimental study of the conduction and absorption mechanisms of Germanium in the temperature range 4.2 - 1.5 K. The results of these studies were mainly devoted to the developments of very far infrared detectors. Germanium (Ge) is a well-known semiconductor element used widely, when doped with small concentration of impurities, for detection of far infrared wavelengths up to 100~m. For doping concentrations less 16 3 than 1.0 x 10 atoms/em, the absorption of radiation in the range 100- 1000~m is very weak Because of the lack of the proper absorption mechanisms, except for some photo-hopping absorption in compensated samples around 1000llm.16 -3 In the range of doping between 1-8 x 10 cm ,there exists additional thermal activation energy not present in the lower concentrations. It was thought that this activation energy results from impurity interactions in this doping range, and hence a delocalized energy band is thus formed above the ground state level. However, the electrical conduction, the width of this band and its position, and the relevance of this band to the marked bolometric effect for 10o-lOOOWU wavelength detections are not yet clear. This thesis presents further study on this band together with its relation to the conduction and absorption mechanisms. Comparative studies were usually made for two samples of Ge differing in doping configuration, one of which does not have this additional activation energy (low concentration) . The firs two chapters give a review of the absorption and conduction mechanisms in Ge at low temperatures, and the performance relations and measurements for different types of infrared detectors. In this report, the conduction mechanism is studied for the two samples, and includes galvanometric properties, thermal properties and energy scattering processes for the carriers in the delocalized band. The absorption characteristics, 1n lOO-lOOO~ru range of the two samples were investigated. Germanium elements with absorbing surfaces are also studied using two different techniques, namely, surface ion implantation and metal film deposition. The mutual effects of the implanted surface and the bulk material are discussed and suggestions for the future of this technique are given. Finally, the design and performance of the constructed high sensitivity far infrared Ge detectors using the higher concentration sample are given. Theoretical noise limitations were reached in these detectors. Heasurements and practicaI. astronomical applications are also given.

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references.

<p> A high-resolution, low-noise far-infrared Fourier transform spectrometer system has been developed and utilized to study optical absorption in the III-V compound semiconductor InSb.</p> <p> Its electron effective mass was investigated, using cyclotron resonance absorption, as a function of magnetic field and compared with a theory originated by Kane (1957). The agreement was good and accurate values of the band edge effective mass and effective g factors were determined. Resonant electron-LO phonon coupling between the n = 2 and n = 0 + wLO Landau levels was observed and the polaron effective mass enhancement measured as a function of magnetic field. Comparison with Larsen's theory (1966), permitted an accurate value of the coupling constant to be derived. The temperature dependence of the electron effective mass was shown to be primarily due to dilation of the crystal lattice in confirmation of other workers' suggestions. However, some discrepancy, whose origin is unknown, was found to exist between experiment and theory.</p> <p> Single phonon absorption by the longitudinal optic phonon mode at the zone center was observed on the side of the main Reststrahl band in a thin sample. The shapes, frequencies and intensities of far-infrared absorptions attributable to two-phonon processes were found to compare favourably with a theoretical two-phonon density of states curve calculated by G. Dolling (1972). The parameters used in the theory were derived from inelastic neutron scattering experiments. Two phonon combinations and their locations in the Brillouin zone which give rise to strong features in the two-phonon density of states were identified by comparing theory and experiment. Important critical points were discovered to be located on or near the zone boundary and not only at the symmetry points X and L as previously suggested. The frequency shifts of some two-phonon features were measured as a function of temperature and analyzed in terms of a quasi-harmonic lattice dilation component and an anharmonic component. The two terms were found to be mirror images as a function of temperature.</p> / Thesis / Doctor of Philosophy (PhD)

<p> High resolution measurements of the far-infrared absorption spectra due to a number of substitutional impurities in KBr and KCl are presented. Several Van Hove singularities of the phonon spectrum of the host lattice are directly observed and found to shift to higher frequencies as the impurity concentration is increased. The first direct experimental evidence for the change of shape or metamorphism of singularities is also presented. The experimental spectra are compared with numerical calculations based on the ordinary shell model for the defect together with phonon data obtained from inelastic neutron scattering experiments. Agreement between experiment and calculation is generally good when impurity resonant modes are absent.</p> / Thesis / Doctor of Philosophy (PhD)