A dilatometer of exceptionally high sensitivity has been developed and used to measure the thermal expansion of polycrystalline samples of copper, silver and gold and of a single crystal of copper in the range 4.2 to 15°K. The results obtained for copper were in excellent agreement with the work of other researchers and the error estimates were sufficiently small to show that the theoretical calculations of Collins are not supported by measurements on a polycrystalline specimen of copper. Below 15°K the data points were well represented by the equation: 1010a=1.54+/-0.04 T+0.275+/-0.0027T 3 The results obtained for a single crystal of copper were significantly different from those obtained for a polycrystalline sample yet they are also in disagreement with the theoretical value. Below 15°K the data fitted the equation: 1010a=3.13+/-0.05 T+0.255+/-0.003T 3 Values of Yo (the low temperature limiting value of the Gruneisen parameter) for silver and gold were measured to be 2.04 +/- 0.06 and 2.91 +/- 0.02 respectively. The agreement with the theoretical values 2.22 and 2.92 is quite good. Below 6°K the thermal expansion of silver and gold was found to be anomalous as it was no longer proportional to the specific heat of these metals. In order to obtain high accuracy in the values of thermal expansion it was necessary to measure temperature to about 0.01°K. For this purpose a method was developed to obtain an interpolation of the resistance versus temperature function in the range 4.2 to 10°K. This capability permitted a theoretical study of the electrical resistivity of pure platinum which indicated that d-band electrons contribute significantly to the conductivity at low temperatures. In the hope of obtaining better measurements of temperature indium resistance thermometers were designed and constructed. Their reproducibilities were measured and were found to exceed previously reported values for indium resistance thermometers.

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Doctor of Philosophy / Department of Physics / Charles L. Cocke / The broad objective of ultrafast strong-field studies is to be able to measure and control atomic and molecular dynamics on a femtosecond timescale. This thesis work has two major themes: (1) Study of high-energy photoelectron distributions from atomic targets. (2) Electron localization control in atomic and molecular reactions using shaped laser pulses. The first section focuses on the study of photoelectron diffraction patterns of simple atomic targets to understand the target structure. We measure the full vector momentum spectra of high energy photoelectrons from atomic targets (Xe, Ar and Kr) generated by intense laser pulses. The target dependence of the angular distribution of the highest energy photoelectrons as predicted by Quantitative Rescattering Theory (QRS) is explored. More recent developments show target structure information can be retrieved from photoelectrons over a range of energies, from 4U$_p$ up to 10U$_p$, independent of the peak intensity at which the photoelectron spectra have been measured. Controlling the fragmentation pathways by manipulating the pulse shape is another major theme of ultrafast science today. In the second section we study the asymmetry of electron (and ion) emission from atoms (and molecules) by interaction with asymmetric pulses formed by the superposition of two colors (800 $\&$ 400 nm). Xe electron momentum spectra obtained as a function of the two-color phase exhibit a pronounced asymmetry. Using QRS theory we can analyze this asymmetric yield of the high energy photoelectrons to determine accurately the laser peak intensity and the absolute phase of the two-color electric field. This can be used as a standard pulse calibration method for all two-color studies. Experiments showing strong left-right asymmetry in D$^+$ ion yield from D$_2$ molecules using two-color pulses is also investigated. The asymmetry effect is found to be very ion-energy dependent.

<p> Observing the non-equilibrium dynamics of the invisible ultrafast atomic and sub atomic world requires optical tools with ultrashort bursts of light and wavelengths. Such optical sources can provide us with the ultimate understanding of the quantum universe in the 4D space-time continuum at femto-zeptosecond time and nano-picometer spatial scale. Revealing at the same time, the 'extra dimensions' of the chemical nature of matter with elemental specificity, e.g., oxidation, charge/spin localization to specific elements, etc. To expand the frontiers of knowledge, there is a simple solution: coherent ultrafast X-ray or gamma&ndash;ray laser light. Amongst the numerous X-ray light sources that exist or have been developed to date, there are just two practical complementary alternatives: giant free electron X-ray laser facilities and compact high harmonic generation X-ray lasers. This thesis focuses on the latter. </p><p> High harmonics result from the extreme nonlinear response of matter to strong laser fields. However, due to inability to phase match, the available bright HHG sources were limited to the EUV spectral region ~0.15<i> keV.</i> We report on two routes for efficiently obtaini bright, coherent X-ray light. The first approach, takes advantage of the ultra-high emission per atom and ion species, the large refractive indices, and small phase mismatch, using high intensity UV lasers. Here the specifics of the phase matching and group velocity matching lead to bright soft X-ray emission from ions and atoms, even at ionization levels above 500%. Using UV light at 0.270<i>&micro;m, </i> the harmonics extend above 280<i>eV</i> while the expec phasematching cutoff was believed to be 23<i>eV</i>. Second, using IR lasers, where the process o phase matching favors the coherent buildup of X-rays from many atomic emitters at high gas density over long distances at extremely low ionization levels. The X-rays supercontinua driven by Mid-IR light at &lambda;_L = 3.9<i>&micro;m,</i> extends over ~12 octaves to > 1.6<i>keV,</i> and broadest spectrum generated to date from any small or large source. Calculations indicate that we can extend further the emission to the hard X-ray region and beyond using high laser intensity UV-EUV lasers or low intensities IR-Far IR lasers, without significantly sacrificing the X-ray flux. However, special highly transmissive fibers are required for phase matching in the Mid-IR region, where the propagation distances are longer than the self-guiding lengths. In addition, the flux from the Mid-IR driven HHG is expected to decrease substantially or cease due to a large <i>v</i> vector &times; <i>B</i> vector drift of the returning electrons caused by th magnetic field <i> B</i> vector and because of the large quantum diffusion of the electron wavepacket. We propose and design special photonic bandgap waveguides to resolve all the issues limiting the flux of IR and Mid-IR and UV driven hard X-rays. </p><p> The properties of the X-rays, driven by UV and IR lasers, are completely contrasting: supercontinuum versus isolated sharply peaked harmonics, we predict chirped isolated single pulses on sub or femtosecond scale as opposed to near transform limited train of attosecond pulses, respectively for IR and UV-driven harmonics. While pressure phase matching has been widely used we introduce the concept of pressure-temperature tuned phase matching for the process of HHG generation that additionally increases the flux. </p><p> Moreover, we report on harmonic generation with extremely high flux at near <i>mW</i> and <i>&micro;J</i> level, that allows us to perform experiments, which were previously only possible in large-scale facilities. While a magnetic scattering cross section is orders of magnitude smaller than the charge scattering cross section, we demonstrate resonant magnetic ptychography coherent diffraction imaging at the <i>Fe, M</i>-edge, using narrow bandwidth X-rays light, to lo at buried magnetic domain structure. Using broad 'water window' and keV coherent X-ray supercontinua, we extract atomic structure on picometer spatial resolution and chemical bonds' information, through x-ray absorption spectroscopy measurements at various absorption edges. </p><p> Such unique light tools will make it possible to answer even questions that have not yet been asked or may have never been imagined.</p><p>

Calculations have been carried out in the distorted-wave Born approximation for electron-impact excitation of the individual 2p fine-structure states of the hydrogen atom. Results are given for 54.4, 100, and 200 eV. The purpose was not to improve on existing more elaborate calculations of the state multipoles of the excited 2p states, but rather to investigate spin-related phenomena, such as an incident polarized beam, polarized target atoms, and the polarization of the scattered electrons when unpolarized electrons are incident on unpolarized target atoms. The bound state wave functions are constructed using the total angular momentum scheme, $\vert JM\sb{J}\rangle = \sum\limits\sb{M\sb{L}M\sb{S}}C(LSJ;M\sb{L}M\sb{S}M\sb{J})\vert LM\sb{L}SM\sb{S}\rangle$, and the Percival-Seaton hypothesis is not used. We then construct explicitly-spin-dependent scattering amplitudes. This approach is to be contrasted with previous calculations which use $\vert LM\sb{L}SM\sb{S}\rangle$ wave functions and assume that the sum of the electron spin projections is conserved in the collision, or with calculations which use uncoupled wave functions. / The spin polarization of the scattered electrons resulting from scattering unpolarized electrons on unpolarized ground state hydrogen atoms (the 'fine-structure effect') is found to result here from interference of the direct and exchange scattering amplitudes. Distortion of the scattered waves by the atomic potential produces a nonzero component of the transferred angular momentum perpendicular to the scattering plane. This orbital angular momentum orientation of the excited atom is then transferred to the scattered electron via angular momentum algebra. The spin-orbit interaction in the excited atom is the origin of the spin polarization, since it produces a sufficient energy separation of the fine structure states to allow them to be studied separately. / Source: Dissertation Abstracts International, Volume: 56-04, Section: B, page: 2085. / Major Professor: W. N. Shelton. / Thesis (Ph.D.)--The Florida State University, 1995.