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In recent years, superconducting radio-frequency (SRF) cavities have been considered as candidates for qubits in quantum computing, showing a significantly longer decoherence time compared to many other realizations. Originally, SRF cavities are the workhorse of modern particle accelerators and ongoing R&D pursuits to improve their properties, to increase the accelerating field and reduce the surface resistance in order to increase the energy reach and duty cycle of accelerators. Although few experimental milestones have been realized, the underlying mechanisms of the still observed losses have not been fully understood. In this contribution we are going to show that a recently reported temperature treatment of Nb SRF cavities in the temperature range of 573-673 K, which reduces the residual surface resistance to unprecedented values, is linked to a reorganization of the niobium oxide and near-surface vacancy structure and that this reorganization can explain the observed improved performance in both applications, quantum computing and SRF cavities.

Doppler and recoil effects are an integral part of the photoemission process at the high kinetic energies reached in hard x-ray photo-electron spectroscopy (HAXPES) and have a major effect on the observed lineshape, resulting in broadening, energy losses and discrete excitations. These effects can be modeled with a high degree of detail for small systems like diatomic molecules, for larger systems such treatment is often superfluous as the fine spectral features are not observable. We present a united description of the Doppler and recoil effects for arbitrary polyatomic systems and offer an approximate description of the recoil- and Doppler-modified photoemission spectral lineshape as a practical tool in the analysis of HAXPES spectra of core-level photoemission. The approach is tested on the examples of carbon dioxide and pentane molecules. The C and O 1s photoelectron spectra of CO2 in gas phase were also measured at 2.3 and 7.0 keV photon energy at Synchrotron SOLEIL and the spectra were analyzed using the model description. The limitations and applicability of the approach to adsorbates, interfaces and solids is briefly discussed.

In recent years, short, pulsed laser ablation has been gaining popularity for machining small scale test geometries from bulk samples and for efficient serial sectioning. These laser-based techniques are being added to the toolbox in material science, which makes it necessary to understand the changes in the material that occur from the laser-material interaction. Positron annihilation spectroscopy is a unique, nondestructive technique to investigate small defects in materials difficult to investigate by other tools. In this work, Doppler broadening and positron lifetime annihilation spectroscopy are utilized to help quantify the damage in materials treated with short, pulsed lasers. Using a femtosecond laser on single crystal silicon, this manuscript shows that clusters of vacancy-like defects and small voids increase systematically with laser power. The damage induced by the laser can also reach to micrometer depths.

The effect of in situ oxygen and vacuum annealings on the low bandwidth manganite Gd1-xCaxMnO3 (GCMO) thin film with x = 0:4 was investigated. Based on the magnetic measurements, the AFM-FM coupling is suppressed by the vacuum annealing treatment via destroying the double exchange interaction and increasing the unit cell volume by converting the Mn4+ to the Mn3+. Consequently, resistance increases significantly compared to pristine film. The results are explained by a model obtained from the positron annihilation studies, where the vacuum annealing increased the annihilation lifetime in A and B sites due to the formation of vacancy complexes VA;B - VO, which was not the case in the pristine sample. The positron annihilation analysis indicated that most of the open volume defects have been detected in the interface region rather than on the subsurface layer and this result is confirmed by detailed x-ray reflection analysis. On the other hand, the effect of oxygen annealing on the unit cell volume and magnetization was insignificant. This is in agreement with positron annihilation results which demonstrated that the introduction of oxygen does not change the number of cation vacancies significantly. This work demonstrates that the modification of oxygen vacancies and vacancy complexes can tune magnetic and electronic structure of the epitaxial thin films to provide new functionalities in future applications.

The non-destructive investigation of single vacancies and vacancy clusters in ion irradiated samples requires a depth-resolved probe with atomic sensitivity to defects. The recent development of short-pulsed positron beams provides such a probe. Here, we combine depth-resolved Doppler broadening and positron annihilation lifetime spectroscopies to identify vacancy clusters in ion irradiated Fe and measure their density as a function of depth. Despite large concentrations of dislocations and voids in the pristine samples, positron annihilation measurements uncovered the structure of vacancy-clusters and the change in their size and density with irradiation dose. When combined with TEM measurements, the study demonstrates that the increase in the density of small vacancy clusters with irradiation is associated with a remarkable reduction in the size of large voids, revealing a novel mechanism for the interaction of cascade damage with voids in ion irradiated materials, a consequence of the high porosity of the initial microstructure.

Voltage control of magnetism through electric field-induced oxygen motion (magneto-ionics) could represent a significant breakthrough in the pursuit for new strategies to enhance energy efficiency in magnetically actuated devices. Boosting the induced changes in magnetization, magneto-ionic rates and cyclability continue to be key challenges to turn magneto-ionics into real applications. Here, it is demonstrated that room-temperature magneto-ionic effects in electrolyte-gated paramagnetic Co3O4 films can be largely increased both in terms of generated magnetization (6 times larger) and speed (35 times faster) if the electric field is applied using an electrochemical capacitor configuration (utilizing an underlying conducting buffer layer) instead of placing the electric contacts at the side of the semiconductor (electricdouble-layer transistor-like configuration). This is due to a greater uniformity and strength of the electric field in the capacitor design. These results are appealing to widen the use of ion migration in technological applications such as neuromorphic computing or iontronics in general.

A recently discovered modified low-temperature baking leads to reduced surface losses and an increase of the accelerating gradient of superconducting TESLA shape cavities. We will show that the dynamics of vacancy-hydrogen complexes at low-temperature baking lead to a suppression of lossy nanohydrides at 2 K and thus a significant enhancement of accelerator performance. Utilizing Doppler broadening Positron Annihilation Spectroscopy, Positron Annihilation Lifetime Spectroscopy and instrumented nanoindentation, samples made from European XFEL niobium sheets were investigated. We studied the evolution of vacancies in bulk samples and in the sub-surface region and their interaction with hydrogen at different temperature levels during in-situ and ex-situ annealing.

The effect of average incorporated ion energy and impinging atomic oxygen flux on the structure and permeability of SiOx thin films by a microwave driven low-pressure discharge with additional RF bias is studied by means of positron annihilation lifetime spectroscopy (PALS) and complementary analytical approaches. The film growth and structure were controlled by the particle fluxes. Acorrelation between the pore sizes and pore size distribution as measured by positron annihilation lifetime spectroscopy (PALS) and the adjusted plasma parameters was established. The corresponding barrier performance was measured by oxygen transmission rate (OTR) and could be explained by the pore size distribution. The dominant pore size characteristic for dangling bonds within the SiOx-network was found to be in the range of 0.8 nm. The chemical composition and morphology were analysed by means of X-ray photoelectron spectroscopy (XPS), FTIR diffuse reflectance measurements (DRIFT) and atomic force microscopy (AFM). It was observed that a combination of both an increase in incorporated energy per deposited Si atom and low oxygen to silicon ratio resulted in an enhanced cross-linking of the SiOx network and thereby lead to a decrease in micropore density and to a shift of the pore size distribution function to lower values.

I explore the limits of how tightly a beam can be focused, and derive a focal parameter for scalar beams that can be symbolically evaluated for most beams, and is guaranteed to be convergent for physical beams, that compares peak in- tensity to the total intensity in the beam profile. I argue that this parameter is superior to spot size, and use this to derive a rigorous limit of focusing for scalar beams. A particular beam known as the proto-beam achieves this tight- est focus possible. I show the generalisation of this measure to electromagnetic beams, and place a lower bound on the focal extent of electromagnetic beams. I also propose the use of exponential regulators as alternatives to moment based measures, as a solution to the convergence issues created by the power law decay of exact solutions. I explore the Doppler shift for finite beams, and how monochromatic beams become polychromatic under a Lorentz boost. The local frequency is also explored, and I show that a deviation of the local frequency from the Doppler frequency will occur due to wavelength broadening near the focus. Lekner and I examine a beam that closely approximates a paraxial Gaussian beam radially, and examine the phase singularities for optical beams that occur near the zeros of the beams wavefunction. We also investigate attempts to find exact solutions with Gaussian profiles, and show that this is impossible; any such beam will be evanescent and exponentially grow. Finally, I investigate the property of finite classical electromagnetic pulses having a zero momentum frame, and show that for quantum single photon pulses this property holds for the expectation value. I show that any individual measurement however, still measures a light-like four-momentum for the photon.

The effect of low energy plasma immersion ion implantation and deposition of titanium on microstructure, defect structure and hydrogen trapping in zirconium alloy Zr-1Nb was studied. Defect structure and distribution were analyzed by Doppler broadening using slow positron beam. The surface microstructure after modification is represented by nanostructured Ti grains with random orientation. The gradient distribution of titanium as well as vacancy type defects were analyzed. The concentration of vacancy type defects is rising with increasing bias voltage. Gas-phase hydrogenation of the Ti-modified Zr-1Nb alloy was performed at 400 °C for 60 min. The strong interaction of hydrogen with vacancy type defects was demonstrated. Two different changes in the defect structure after hydrogenation were observed: when a titanium film is formed on the surface (after deposition at 500 V) hydrogen trapping occurs with the formation of titanium hydride phases, while in the implanted layer (deposition at 1000 and 1500 V) hydrogen is trapped due to interaction with vacancy type defects. The physical basis of Ti diffusion and its influence on the evolution of defect structure after surface modification and hydrogenation were discussed.

Doppler broadening plays an important role in laser rovibrational spectroscopy of trapped deuterated molecular hydrogen ions (HD+), even at the millikelvin temperatures achieved through sympathetic cooling by laser-cooled beryllium ions. Recently, Biesheuvel et al. (2016) presented a theoretical lineshape model for such transitions which not only considers linestrengths and Doppler broadening, but also the finite sample size and population redistribution by blackbody radiation, which are important in view of the long storage and probe times achievable in ion traps. Here, we employ the rate equation model developed by Biesheuvel et al. to theoretically study the Doppler-broadened hyperfine structure of the (v,L):(0,3)→(4,2) rovibrational transition in HD+ at 1442 nm. We observe prominent yet hitherto unrecognized ghost features in the simulated spectrum, whose positions depend on the Doppler width, transition rates, and saturation levels of the hyperfine components addressed by the laser. We explain the origin and behavior of such features, and we provide a simple quantitative guideline to assess whether ghost features may appear. As such ghost features may be common to saturated Doppler-broadened spectra of rotational and vibrational transitions in trapped ions composed of partly overlapping lines, our work illustrates the necessity to use lineshape models that take into account all the relevant physics.

Multilayer ultrathin-films with perpendicular magnetic anisotropy (PMA) show a perspective as candidates for spintronic devices. The effective magnetic anisotropy strongly depends on the magnetic layer thickness – spin reorientation transition (SRT) at a critical thickness takes place from the inplane to out-of-plane magnetization direction. Moreover, SRT can be shifted to higher thicknesses by means of ion [1] and fs-laser irradiation [2]. Here, we employ variable energy positron annihilation spectroscopy (PAS) that is sensitive to open volume defects and their atomic surrounding to compare these two methods of the SRT inducement. Molecular beam epitaxy deposited films with different bottom Pt layer thicknesses and growth temperatures have been investigated. In case of Ar+ ion irradiated trilayers magnetization can be driven to the out-of-plane state twice as a function of ion fluence [1], whereas our preliminary studies of UV laser irradiation suggest only one SRT. PAS analysis (Fig. 1) of the as-grown samples reveal slight differences in crystal quality and defect concentration that is likely due to a thicker bottom Pt layer used for the ion irradiation experiment. Films utilized for the laser irradiation exhibit larger initial positron diffusion length, L+ that is close to L+ of the substrate (~60nm). In case of lower ion and laser fluences only minor and no interface intermixing has been found, respectively. The sample irradiated with lower ion fluence shows a slight increase of S (for E~1.5keV) being likely due to Co-vacancy increase, which could be responsible for first SRT. The sample irradiated with lower laser fluence shows no difference compare to the asgrown stacks, where only increase of magnetic anisotropy was found. The larger ion and laser fluences reorients magnetization to the out-of-plane state that is evidenced by both magneto-optical and PAS studies – S(E) curves nicely overlap. Moreover, large intermixing is expected, thus creation of the CoPt

The formation of vacancies in SrTiO3 due to annealing in vacuum [1] or low-energy ion irradiation [2] also leads to the modification of electronic properties that could be exploited in applications like resistivity switching. Here, we employ both these modification methods combined with in-situ defects evolution analysis by means of Doppler Broadening Positron Annihilation Spectroscopy (DB-PAS). Two reference SrTiO3 single crystals, undoped and Nb-doped have been investigated. Vacuum annealing of undoped SrTiO3 increases the defect concentration which can be attributed to the creation of oxygen and strontium vacancies close to the sample surface and deeper inside the substrate, respectively. Variable energy DB-PAS reveals the depth-dependent open volume defects concentration. Second, in-situ room and low temperature (about 165K) Ar+ irradiation has been utilized as a preliminary attempt to understand a vacancy migration process beneath the kinetical ion penetration depth. For that purpose, a frozen vacancy state is required, which could be achieved by lowering the system temperature below the vacancy activation energy. Although, that part of the experiment has been not entirely successful due to not low enough temperature realized during ion irradiation, however, a strong conclusion has been drawn about necessity of performing such type of experiments in-situ. A clear indication of oxygen deficiency at the sample surface due to ion irradiation, as found from DB-PAS is diminished after repeated ex-situ measurements.

The transport properties of a series of Si and SiC diodes have been studied using the Ion Beam Induced Charge (IBIC) technique. Structural defects were induced into the samples during the irradiation with 17 MeV protons. The experimental values of the charge collection efficiency (CCE) vs bias voltages have been analyzed using a modified drift-diffusion model, which takes into account the recombination of carriers in the neutral and depletion regions. From these simulations, we have obtained the values of the carrier's lifetime for pristine and irradiated diodes, which are found to degrade faster in the case of the SiC samples. However, the decrease of the CCE at high bias voltages is more important for the Si detectors, indicative of the lower radiation hardness of this material compared to SiC. The nature of the proton-induced defects on Si wafers has been studied by Positron Annihilation Spectroscopy (PAS) and Doppler Broadening Spectroscopy (DBS). The results suggest that the main defect detected by the positrons in p-type samples is the divacancy while for n-type at least a fraction of the positron annihilate in another defect. The concentration of defects is much lower than the number of vacancies predicted by SRIM.

Positron annihilation lifetime spectroscopy serves as an excellent tool for studies of open-volume defects in solid materials such as vacancies, vacancy agglomerates, dislocations, pores and voids. The intense mono-energetic positros beamline (MePS) at the ELBE accelerator developed for positron life-time and conventional Doppler Broadening experiments offers a non-destructive investigation method to study of porous media as well as thin film as a function of thickness.

Hydrogenated Amorphous Silicon (a-Si:H) is a very promising solar cell material with a good potential to use in many applications, as it is cheap to produce, light-weight and flexible. However, upon prolonged exposure to light, the layers suffer from both metastable and irreversible changes (the Staebler-Wronski effect) that have a bad effect on the photoconductivity. Annealing the material up to 150-200oC removes the metastable changes. The Staebler-Wronski effect has been studied for over 35 years, but the mechanisms behind it are not fully understood yet. In this project an attempt is made to increase the understanding by examining the nanostructure of rf-PECVD produced a-Si:H samples, in particular the nanostructural evolution, as a function of annealing temperature (up to 800oC) and hydrogen dilution. Positron Annihilation Spectroscopy techniques, sensitive to even the smallest vacancies, are used to study the electron environment of the open volume defects. These techniques include Doppler broadening positron annihilation spectroscopy, two-dimensional angular correlation of annihilation radiation and coincidence Doppler broadening (DB-PAS, 2D-ACAR and CDB). Neutron Reflectometry is used to study the hydrogen content as a function of film depth. Raman spectroscopy is used in addition to the annealing experiment to detect the presence of molecular hydrogen. Clear evidence is found that dilution with hydrogen causes a broadening of the electron momentum distribution. DB-PAS and 2D-ACAR results strongly indicate that this broadening is due to a decrease in the average size of the open volume defects., Applied Physics, Applied Sciences

A study of irradiation-induced damage in HAVAR® foils was initiated in order to extract the highest proton dose the foils can sustain. The lattice structure of HAVAR® foils in different metallurgic conditions is presented, as well as visible internal structure, measured by Transmission Electron Microscopy (TEM). Positron Annihilation Spectroscopy (PAS) techniques were used to investigate these foils, and another foil that had been irradiated to the maximal proton dose limit, set by the manufacturer, of 1 mAh. PAS techniques included Doppler Broadening (DB) measurement in the SPONSOR beam and Lifetime (LT) measurements, both carried at Helmholtz Zentrum Dresden-Rossendorf (HZDR). Both positron spectroscopy methods show clear differences between the investigated foils, with distinguished characteristics for annealed, cold-rolled and irradiated foils. The advantages of using a slow positron beam to study thin foils and defect profiles, over a table-top LT spectrometer, are discussed and demonstrated by the HAVAR® measurements.

Electroluminescence in SiO2 layers can be created by Ge implantation and a subsequent heat treatment, leading to the formation of Ge nano-particles inside the SiO2. An additional implantation of Er, connected with a further annealing, can lead to an improvement of the luminescent properties. However, the intensity of electroluminescence was found to decrease drastically after exceeding an optimum concentration of the Er doping. Slow positron implantation spectroscopy (SPIS), both in single (DB) and coincidence (CDB) Doppler broadening mode, was applied to probe processes at a microscopic level which might have an impact on the optical response. It shows that the increasing intensity of the electro-luminescence is connected with a crystalline structure of the SiO2 covering the nano-particles and also with the improved reverse energy transfer process between Er and Ge.

We obtained evidence for the partial chemical segregation of as-deposited and hydrogenated Mg1?yTiy films (0 ? y ? 0.30) into nanoscale Ti and Mg domains using positron Doppler-broadening. We exclusively monitor the hydrogenation of Mg domains, owing to the large difference in positron affinity for Mg and Ti. The electron momentum distribution broadens significantly upon transformation to the MgH2 phase over the whole compositional range. This reveals the similarity of the metal-insulator transition for rutile and fluorite MgH2. Positron lifetime studies show the presence of divacancies in the as-deposited and hydrogenated Mg-Ti metal films. In conjunction with the relatively large local lattice relaxations we deduce to be present in fluorite MgH2, these may be responsible for the fast hydrogen sorption kinetics in this MgH2 phase., Radiation, Radionuclides and Reactors, Applied Sciences

Diagnostic measurements play a vital role in experiments. Without them we would be in the dark with no way of knowing what was happening; of understanding the processes and behaviour occurring; or even of judging the success or failure of our experiments. The development of fusion plasma devices is no different. In this thesis we concentrate on visible spectroscopy based diagnostics: examining the techniques for measurement and analysis; the breadth of plasma parameters that can be extracted from the spectroscopic data; and how the application of these diagnostic techniques gives us a broader picture of the plasma and the events taking place within. Techniques are developed and applied to plasmas in three fusion experiments, EXTRAP T2R, ASDEX Upgrade and JET. The diagnostic techniques exploit different features of the measurements of the emitted photons to obtain various useful plasma parameters. Determination of the ion temperature and rotation velocity of oxygen impurity ions in the EXTRAP T2R plasma is achieved through measurement and analysis of, respectively, the Doppler broadening and the Doppler wavelength shift of visible wavelength atomic spectral lines. The evolution of the temperature and rotation is studied as a function of the discharge parameters, in particular looking at the effect of applying active feedback control schemes to the resistive wall modes and/or pulsed poloidal current drive. Measurements of multiple ionisation stages are used to estimate radial profiles of the toroidal rotation and the ion temperature and correlations between the ion rotations and the rotation velocities of tearing modes are also established. Radial profiles of the emissivity and density (or concentration) of the oxygen ions are obtained by means of measurements of the spectral line intensities on a small array of linesof- sight through the plasma. Changes to the profiles for different plasma schemes and the implications for particle transport are investigated. The deri, QC 20100810

Ultra-fine grained copper prepared by high-pressure torsion has been studied by means of positron annihilation techniques (slow positron implantation spectroscopy,conventional positron lifetime and Doppler broadening measurements) combined with transmission electron microscopy, X-ray diffraction and microhardness measurements. Dislocations in distorted regions along grain boundaries and microvoids of size 3-4 vacancies inside grains were identified and their lateral distribution and depth profile were investigated in detail. The concentrationof microvoids has been found to decrease with depth and to vary slightly with the distance from specimen axis, being lowest in the centre of the specimen disc. No position dependence of the concentration of dislocations was observed.

This project was designed to identify applications of THz technology of potential interest to the DoD and to provide a technical introduction for DARPA personnel to the underlying scientific and technical issues. The final report begins with a discussion of the physics which governs the interactions between radiation and matter in the THz, with emphasis on the differences between low pressure gases, atmospheric pressure gases, and solids. Atmospheric propagation is considered as an example. Two specific applications were developed in more detail. The first is a concept for a point detector of gases, which is based on the absolute specificity of rotational spectra in the THz. The second is a remote detection scheme which makes use of THz/IR double resonance. The former is based on well understood science and the risks for the development of-such a program lie in the trade-offs against alternative solutions as a function of scenario. Although the details of application scenarios are not known to the authors, it is highly likely that some of them are very favorable. The latter is a high risk/high payoff scheme whose eventual utility depends not only upon application scenario, but also on currently unknown scientific parameters.

A broad program to investigate the nonlinear optical properties of a new type of dense atomic medium has been undertaken. This medium consists of a dense, diverging supersonic atomic beam for which the Doppler broadening is nearly eliminated by means of a magnetic field gradient. Research has been focused on characterizing the coherent radiation of the medium when it is prepared by continuous spatially separated optical fields. Spatial, directional, and coherence properties of the coherent field, including its quantum noise, have been investigated.

Research is currently underway to investigate the physical mechanisms that cause loss of temporal coherence in scattered light. The results of experiments that measure coherence length versus temperature, optical path length, and water quality are reported. It is shown that the loss of temporal coherence is caused by spectral broadening. Based on these results and research into the causes of spectral broadening, experiments are proposed to measure each type of broadening mechanism, with a much higher degree of accuracy.

This report discusses the experimental and theoretical work carried out associated with the use of resonance refractivity to improve flow visualization. The principal accomplishment of the present study was to verify quantitatively the feasibility of using the near-resonance spectral region around the sodium D-lines for obtaining one-to-two order-of-magnitude increase in the sensitivity of refractive methods of flow visualization such as schlieren, interferometric and shadow techniques. It is in this near region of the line wings, typically a few angstrom from line center, that the trade-off between refraction and absorption is highly favorable to permit implementation of the method with an available tunable dye laser light source. Here, the refractivity is high enough to see sound waves, weak vortices, etc. The accomplishments included a combined theoretical and experimental analysis of the near-region refractive and absorptive profile taking into account both doppler and collision broadening. The latter feature included studies to optimize the choice of collision parameters for self-broadening (pure sodium vapor) and for heterogeneous broadening (sodium highly diluted by a carrier gas in a flow facility). Experiments with an interferometer-heat pipe arrangement using a tunable pulsed dye laser gave results which agreed with the analysis. The technique is now at the facility-design stage.

The scattering of acoustic waves from a randomly varying wind-driven water surface is known to introduce both time and frequency spreading of the received signal. The frequency spreading is thought to be related to surface statistics and water wave motion. Therefore, knowledge of this relation leads to the possibility of predicting surface statistics by analysis of the received acoustic signal. One important feature of the frequency spreading function is that the Doppler sidebands are not equal in magnitude on both sides of the carrier. Unequal sidebands are predicted if the acoustic source and receiver are not located at the same depths below the water surface and if the direction of the surface wave motion is not perpendicular to the vertical plane containing both the source and the receiver. Experimental results from a model tank operated under various wind conditions have verified the existence of unequal Doppler sidebands under these conditions. However, strong asymmetries in sidebands were also observed under conditions under which the previous theory would have predicted no asymmetries at all. For example, strong asymmetries have been observed in the crosswind direction. This research is to explain the asymmetries not predicted in previous theory but discovered under laboratory operations, and to predict other asymmetries not yet found in either the experimental or the theoretical phase.

A new feature of optical free induction decay (FID) is observed in a coherently prepared sample of 13CH3F by the method of Stark switching. The preparative phase is due to the resonant steady state excitation by a cw laser beam and is followed by FID upon sudden application of a d.c. Stark field that switches the molecular sample out of resonance. The emission is not observed as a simple decay but instead appears as a train of sharp pulses regularly spaced in time due to a repetitive interference. This situation arises because an entire set of infrared transitions within the Stark split manifold are initially prepared, in contrast to our previous study of a nondegenerate transition. The emission, which beats with the laser, produces a heterodyne beat spectrum consisting of a set of regularly spaced frequencies that is the Fourier transform of the slowly decaying pulse progression observed. We thus demonstrate what is the optical analog of the well known NMR method of high resolution pulse Fourier spectroscopy. The detailed behavior of the pulse train agrees well with a FID theory that assumes the transitions to be uncoupled. The subtle behavior of FID near the time origin is explored also by approximate analytic expressions that reveal a near zero or a sizable amplitude depending on the degree of saturation in the preparative stage.

The quantitative measurement of the anomalous dispersion of the P1(6), P1(7), and P1(8) vibration-rotation transitions of hydrogen-fluoride (HF) in absorption are reported. The measurements were performed with a small, line-selectable HF laser equipped with a piezoelectrically frequency-scanned cavity that illuminated a Mach-Zehnder interferometer, one arm of which contained the HF absorption cell. The fringes produced by the interferometer and their dispersion-induced shift were observed directly with the help of a rotating mirror and an ir detector. This interferometer technique has an ultimate noise-limited sensitivity of 0.02 of a fringe spacing at 2.7 micron. Measurements also are given for the absorption coefficient at line center for the same three P1 lines of HF. Both dispersion and absorption measurements are for a pressure range of 0.05 to 10 Torr of pure HF at room temperature, so the absorption lines were Doppler broadened. The measured values for the absorption coefficient and the slope of the dispersion curve at line center and for the maximum excursion of the anomalous refractive index are in excellent agreement with calculated values for these quantities. (Author)

The physical contributions causing various types of spectral lines are described. The conventional combined effects or Voigt profile is derived. A mathematically consistent line shape theory is proposed and equations are derived. Applications of the resultant Voigt, Sung, and Fowler theory are presented and its relevance discussed.

The report describes research to obtain higher power output from CO2 lasers. This involved the study of the effect of higher order transverse and longitudinal mode excitation.

In pure air at elevated temperatures there are a number of source of infrared radiation (e.g., electron scattering). However, unless the temperature is excessively high (> approx. 5000 K), the only significant source consists of the vibrational transitions of the nitric oxide molecule. Thus, for those portions of the wake of a re-entry vehicle where the temperature is not excessive and ablation of the surface material is not significant, the infrared radiation emitted can be identified with the vibrational bands of NO. In this memorandum a method for calculating the spectral intensity of band radiation is described and results of a calculation of the spectral intensity in the fundamental and first overtone bands of NO for the wakes of two different vehicles are given. Other aspects of infrared wake radiation have been discussed elsewhere.

The sodium D2 line Doppler profile was measured from observed fluorescence of the electronically excited sodium atom generated by photodissociation of NaI by ultraviolet wavelength light in the 2100-2500A region. The experimentally determined Doppler profile is compared to an ideal Doppler profile calculated by considering the vibrational and rotational states of the NaI molecule and by considering the excited sodium atom recoil velocities and the most probable NaI thermal speeds. Effect of polarization of the exciting ultraviolet on the angular velocity distribution of the dissociation products of NaI was measured.

Spectroscopic analysis of the cathode jet of a model coaxial magneto- plasma dynamic (MPD) thruster is conducted to determine electron density and temperature downstream from the cathode. H(Beta) line profiles were scanned from an argon-hydrogen plasma generated in the cathode test facility of the NASA Jet Propulsion Laboratory in Pasadena, CA. A computer program was written in IDL to determine the profile Doppler and Stark half widths, which were used to determine temperature and electron density, respectively. Three sets of data from the cathode test facility were taken, while varying operating voltage, current, hydrogen/argon ratio, and pressure. Radial profiles for electron density and temperature were determined within the cathode jet. Generated plasmas ranged in electron density and temperature from approximately Ne = 2 x 10(14) cm( -3) at 5000 K (0.43 eV) to 4 x 10(14) cm( -3) at 15600 K (1.3 eV). It was determined that radial density and temperature distribution within the cathode jet are essentially uniform, http://archive.org/details/linebroadeningan00bull, Lieutenant, United States Navy, Approved for public release; distribution is unlimited.