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.

Some physicochemical properties of several series of transition metal chalcocarbonyls such as ((eta)('6)-C(,6)H(,6))Cr(CO)(,2)(CX) and Cr(CO)(,5)(CX) (X = O, S, Se) have been investigated. In particular, the infrared, ('13)C and ('17)O nuclear magnetic resonance and ultraviolet spectra have been examined. The results show that the order of (sigma)-donor and (pi)-acceptor capabilities of the ligands is CO CS. The M((pi)) (--->) CX((pi)*) ultraviolet charge-transfer bands are shown to correlate with the respective (mu)'(,MCX) and ('13)C NMR data. Also, the ('13)C NMR chemical shifts and GQVFF force constants are found to be highly correlated. The ('17)O NMR spectra of the metal chalcocarbonyl complexes display chemical shifts in the opposite direction to the corresponding ('13)C ones. No correlation is found between the ('17)O shieldings and the other spectroscopic data. Reaction of Cr(CO)(,5)(CX) (X = S, Se) with halide ions (Y('-)) afforded mixtures of {Cr(CO)(,5)Y}('-) and trans-{Cr(CO)(,4)(CX)Y}('-) while Cr(CO)(,5)(CS) reacted with cyclohexylamine to give Cr(CO)(,5)(CNC(,6)H(,11)). The similarities and differences in the physicochemical behaviour of the metal chalcocarbonyls compared to related systems are discussed in the light of the different bonding patterns.

Bibliography: leaves [250]-268 / 268, ca. 130 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics, 1983

Thesis (M.S.)--University of Pittsburgh, Department of Chemistry, 2007. / Thesis advisor: Sanford A. Asher. Also available as an electronic book in PDF on the University of Pittsburgh Library Web site. Bibliography: p. 37-41.

The Z-pinches in a vacuum spark can be classified into slow, fast and superfast according to their pinch durations. Their emission characteristics are investigated in the visible, ultraviolet and the X-ray wavelengths. The plasma during a fast pinch was found to have an electron temperature between 100 and 600eV. The superfast pinch resulted in a minute cylindrical plasma approximately 40 μm in diameter, with an electron temperature of 1 to 4keV and a lifetime of less than 4ns. The slow and the fast pinch were found to be in agreement with the theoretical results predicted by a shock wave model. The formation of the superfast pinch and its associated high density and temperature were explained as the results of magnetohydrodynamic instability. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The large band gap (approximately 11.5-12.1 eV) and high transmission of calcium fluoride (CaF2) crystal in the ultraviolet (UV) and vacuum ultraviolet (VUV) region makes it an important material for optics for laser applications in UV. However, CaF2 degrades during long exposure to UV irradiation due to defect generation. The formation of selftrapped excitons (STE) is considered the first step in defect generation. In this project the possibility of observing STE states in CaF2 using a narrow bandwidth tunable VUV laser source is investigated. This is the first spectroscopy study of an alkaline earth fluoride using VUV tunable laser radiation instead of a fixed wavelength laser. The use of a VUV tunable laser source has potential for determining the energies of the STE states, which are unknown. Our main objective is addressed by developing techniques to measure absorption spectra of pure and doped CaF2 samples, using a VUV scanning monochromator and a tunable VUV laser, and by doing a literature study. The results obtained with the scanning monochromator show absorption features in 126-180 nm range of all our samples. These vary for different samples and correlate with information from the supplier on the samples’ fluorescence spectra. Total absorption of the VUV light by CaF2 in the 115-126 nm range is observed. With the narrow bandwidth tunable laser light, absorption spectra were obtained in the range of 143-146.7 nm of all our CaF2 samples. No significance peaks which can be related to the STE states in CaF2 were observed in the VUV laser absorption spectra, but the results are valuable to improve the technique. The conclusion is that either a different spectral range or fluorescence detection can be investigated in future. / AFRIKAANSE OPSOMMING: Die groot bandgaping (ongeveer 11.5-12.1 eV) en hoë transmissie van kalsiumfluoried (CaF2) kristal in die ultraviolet (UV) en die vakuum ultraviolet (VUV) gebied maak dit ’n belangrike materiaal vir optika vir laser toepassings in die UV. CaF2 degradeer egter gedurende langdurige blootstelling aan UV lig as gevolg van die generering van defekte. Die vorming van ’n elektron-holte paar wat deur die kristalstuktuur gestabiliseer word teen rekombinasie (self-trapped excitons, afgekort STE) word beskou as die eerste stap in defek generering. In hierdie projek word die moontlikheid ondersoek om STE toestande in CaF2 waar te neem deur die gebruik van ’n afstembare VUV laserbron met emissie in ’n smal spektrale band. Dit is die eerste spektroskopiese studie van ’n aardalkali-fluoried deur die gebruik van afstembare VUV laserlig in plaas van ’n vaste golflengte laser. Die gebruik van ’n afstembare VUV laserbron het potensiaal vir die bepaling van die energieë van die STE teostande, wat onbekend is. Ons hoofdoel word aangespreek deur die ontwikkeling van tegnieke vir die meet van absorpsie spektra van suiwer en gedoteerde CaF2 monsters met behulp van ’n VUV skanderende monochromator en ’n afstembare VUV laser, en deur ’n literatuurstudie. Die resultate wat behaal is met die skanderende monochromator toon die absorpsieprofiele van al ons monsters in die 126-180 nm spektrale gebied. Die absopsieprofiele varieer vir die verskillende monsters en korreleer met die inligting van die verskaffer oor die fluoressensie spektra van die monsters. Totale absorpsie van die VUV lig deur CaF2 in die 115-126 nm gebied is waargeneem. Met die smalband afstembare laserlig is absorpsie spektra in die 143-146.7 nm gebied vir al ons CaF2 monsters verkry. Geen beduidende pieke wat verband hou met die STE toestande in CaF2 is waargeneem in die VUV laser absorpsie spektra nie, maar die resultate is waardevol vir die verbetering van die tegniek. Die gevolgtrekking is dat of ’n ander spektraalgebied of fluoressensiedeteksie in die toekoms ondersoek kan word.

Thesis (PhD (Physics))--University of Stellenbosch, 2006. / Carbon monoxide (CO) is a diatomic molecule of particular interest in astrophysics, due to its high abundance in interstellar space. The Fourth Positive System A1Π−X1Σ+ of CO is an important feature in the vacuum ultraviolet (VUV) region of the electromagnetic spectrum in astronomical observations, especially in high-resolution spectra recorded by satellite-based spectrographs. The interpretation of these astronomically detected spectra requires accurate laboratory wavelengths to serve as rest wavelengths and to resolve possible Doppler-shifts. Such rest wavelengths are known for the 12C16O, 13C16O and 12C18O isotopomers for all astronomically observed spectral lines of the Fourth Positive System. The only laboratory wavelengths currently available for the Fourth Positive System of the 12C17O isotopomer have been determined in a previous work carried out in our laboratory for the vibronic band A1Π(v0 = 3)−X1Σ+(v00 = 0). The present study continues this work for the other vibronic bands which have been detected astronomically, namely A1Π(v0 = 2 − 5)−X1Σ+(v00 = 0). The A1Π(v0 = 0− 1)−X1Σ+(v00 = 0) vibronic bands have also been investigated due to their probability for future astronomical detection. Rotationally-resolved spectra of these six vibronic bands were obtained by selective rovibronic laser excitation, and subsequent detection of the undispersed fluorescence, observed as a function of the excitation wavelength in the VUV. A tunable narrow-bandwidth VUV laser source is used for excitation, and the CO gas sample is introduced by supersonic expansion. Flow-cooling in the supersonic expansion to rotational temperatures roughly corresponding to temperatures in the interstellar medium simplifies and aids the spectral analysis of the spectral lines of interest. The cold conditions in the supersonic expansion facilitates a high sensitivity for detection of the low-J lines, and allows the detection of rare isotopomers of CO in natural abundance. The experimental setup has been improved in the present study by the addition of a vacuum monochromator, facilitating an improved characterisation of the VUV source. Furthermore, a number of experimental conditions have been optimised for the detection of rare CO isotopomers, significantly increasing the signals of these lines in the spectra. The combination of this increase in sensitivity and the addition of the vacuum monochromator to the experimental setup, allowed the simultaneous detection of absorption spectra with the fluorescence spectra as an additional source of information in spectral analysis. The increased sensitivity also contributed to the detection of a large number of spectral lines of interest, with some additional lines identified in the previously studied vibronic band. Spectral lines of 12C16O, 13C16O, 12C18O and 12C17O were detected in each vibronic band, allowing accurate calibration of the spectra. A total of 29 new lines of 12C17O were recorded in the six vibronic bands investigated. Additionally, 10 new singlet-triplet lines of 12C16O were recorded in the wavelength regions investigated. The new wavelengths of 12C17O have been applied to calculate consistent heliocentric velocities of a gas cloud toward the star X Persei, obtained from spectra of the different CO isotopomers taken by the Hubble space telescope.

Transition metal-ligand interactions in several groups of closely related organometallic complexes are discussed from the results of both valence and core photoelectron experiments. Particular attention is given to the novel experimental aspects, including a charged particle oscillator He II source, sample introduction and containment, and data collection and spectral analysis procedures not normally associated with gas phase photo-electron spectroscopy. The application of the ionization experiments begins with a reassessment of the bonding in the group VIb metal hexacarbonyls. He I ionization data of unprecedented quality for the predominantly metal d t₂g level of Cr(CO)₆ and W(CO)₆ reveals for the first time the presence of metal-carbon vibrational fine structure. These positive ion M-C stretching frequencies are significantly reduced from neutral ground state values, giving direct evidence of the pi back-bonding nature of the t₂g level. The next chapter focuses on the comparison of the metal-nitrosyl interactions in the trans-X-W(CO)₄NO complexes to the isoelectronic/isostructural metal-carbonyl interactions in the X-Re(CO)₅ complexes (X = Cl,Br,I). A further comparison of carbonyl and nitrosyl bonding, as well as the first photoelectron assessment of metal-thionitrosyl bonding, is addressed in the next chapter by comparing the valence and core ionization data for CpCr(CO)₂NO and CpCr(CO)₂NS (Sp = η⁵-C₅H₅) to the data reported earlier for CpMn(CO)₃ and CpMn(CO)₂CS. The final chapter of the dissertation compares the electronic structure of the CpFe(CO)₂X complexes to their CpCr(NO)₂X analogs (X = Cl,Br,I,CH₃,CN). The essence of this work fully contrasts the Fe(CO)₂ and Cr(NO)₂ functional groups.

A presente dissertação tem por objetivo o estudo de interações eletrônicas entre o grupo carbonila e o átomo de enxofre em &#945; em alguns alquiltio-tioacetatos de etila (I a,b,c,d,e) ainda não descritos na literatura.RSCH2COSEt I R=C3H7 (a); C4H9 (b); (CH3)2CHCH2 (c); (CH3)2CH (d); (CH3)3C (e) É apresentado um apanhado bibliográfico sôbre a transferência de carga que ocorre intramolecularmente, no espaço, nos compostos carbonílicos contendo na molécula uma dupla etilênica, um átomo de nitrogênio, enxôfre ou selênio. Êle demonstra que a posição relativa dos grupos tem grande importância na interação eletrônica existente. São descritas as sínteses e as caracterizações dos cinco alquiltio-tioacetatos de etila (I a,b,c,d,e). São apresentadas as medidas no infravermelho e ultravioleta dêstes mesmos compostos. Os espectros no infravermelho demonstram um deslocamento da banda de carbonila para frequências menores de aproximadamente 16 cm-1, em relação à dos tioésteres não substituídos. Os espectros no ultravioleta, medidos em n-hexano, não são superposições dos espectros de tioésteres e tioéteres, desde que contêm uma banda larga, em aproximadamente 290 m&#181; (log &#949; ~ 2,6) que é ausente nestas duas classes de compostos. São, também, descritas as tentativas de obter uma inforomação sôbre a natureza da banda de absorção no ultravioleta pelas medidas em solventes polares. Porém, tanto o emprêgo de solventes próticos como apróticos não permitiu perceber qualquer deslocamento da ,banda de absorção, fato este que se deve, principalmente, a dificuldade de se determinar os máximos de absorção. Os resultados espectroscópicos obtidos no presente trabalho estão de acôrdo com os obtidos, anteriormente, pelo grupo orientado pela Profª. Wladislaw, para compostos semelhantes ( I; R = C2H5 ou CH2C6H5). O fato de não se observar qualquer deslocamento da banda de absorção no ultravioleta em t-butiltio-tioacetato de etila (Ie) em relação aos outros alquiltio-derivados permite concluir que o aumento da densidade eletrônica no enxôfre pelo efeito indutivo dos grupos metila não tem influência sobre a interação eletrônica ocorrente nêstes compostos. São apresentadas três possíveis conformações dos compostos estudados e sugeridas as prováveis transições eletrônicas que posSam ocorrer em cada uma delas. A possibilidade de decisão entre estas transições pelo estudo de compostos com as conformações fixas é aventada. / Abstract not available.