Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Includes bibliographical references (leaves 212-213). / by Mark Robert Metzger. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1995. / Includes bibliographical references (p. 173-177). / by Michael S. Chapman. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2007. / Includes bibliographical references (p. 49-50). / We investigate the use of an Amptek Cool-X X-ray Generator for an instructional tool in the physics of x-rays, as well as a source for x-rays for crystal diffraction experiments. The x-ray source is a solid-state two-phase air-cooled source with a time-varying photon output. Two detectors are used in this experiment, the first being an Amptek X-123 Spectrometer and the second a combination scintillator/Polaroid film setup. We collimate the x-ray beam and determine that the system, although low flux and low resolution, will function as a quick and easy tool for the investigation of x-ray physics. / by Louis Edward Fernandes. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, February 2007. / Includes bibliographical references (p. 258-280). / This thesis presents experiments in which a strongly interacting gas of fermions was brought into the superfluid regime. The strong interactions are induced by a Feshbach scattering resonance that allows to tune the interfermion scattering length via an external magnetic field. When a Fermi mixture was cooled on the molecular side of such a Feshbach resonance, Bose-Einstein condensation of up to 107 molecules was observed. Subsequently, the crossover region interpolating between such a Bose-Einstein condensate (BEC) of molecules and a Bardeen-Cooper-Schrieffer superfluid of long-range Cooper pairs was studied. Condensates of fermion pairs were detected in a regime where pairing is purely a many-body effect, the pairs being stabilized by the presence of the surrounding particles. Superfluidity and phase coherence in these systems was directly demonstrated throughout the crossover via the observation of long-lived, ordered vortex lattices in a rotating Fermi mixture. Finally, superfluidity in imbalanced Fermi mixtures was established, and its Clogston limit was observed for high imbalance. The gas was found to separate into a region of equal densities, surrounded by a shell at unequal densities. / by Martin W. Zwierlein. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 199-211). / Radio frequency (rf) waves in the ion cyclotron range of frequencies (ICRF) are widely used for heating fusion plasmas. In a multi-ion-species plasma, the launched fast waves convert to ion cyclotron waves and ion Bernstein waves in the vicinity of the two-ion hybrid resonance between the cyclotron resonances. The mode converted waves are of interest as actuators to optimize plasma performance through current drive and flow drive. Numerical simulations are essential to describe these processes accurately in a realistic tokamak geometry, and it is important that these simulation codes be validated against experiment. The phase contrast imaging (PCI) technique has been used on Alcator C-Mod to measure directly the rf waves. The measurements were compared to predictions of full-wave simulations using a synthetic diagnostic method. The measured mode converted wave intensity was found to be a factor of ~50 weaker than what was expected from the linear wave theory in a strong mode conversion regime. The agreement improved when the wave intensity was weaker, which is a possible indication of nonlinear wave physics being involved. / by Naoto Tsujii. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1999. / Includes bibliographical references (leaves 67-68). / by Edward Richard Karat. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Physics, 1998. / Includes bibliographical references (leaf 31). / by Peter Chien. / B.S.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 51). / It is currently well-known how to lock an optical cavity on resonance using the Pound- Drever-Hall technique. It is also possible to lock a cavity at a single detuned length using an amplitude modulated laser beam. However, there are many interesting applications, that would benefit from the use of a Universally Tunable Modulator (UTM), because it can create any ratio of amplitude to phase modulation. The unique transfer function of the UTM allows for cavity locking at any of the intermediate points between resonance and about half a linewidth of detuning. In this thesis, we construct such a UTM and verify experimentally that the modulator can indeed be used for continuous detuning of optical cavities. / by Emily Davis. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005. / Includes bibliographical references (leaves 55-56). / Recent technological advances have allowed for the construction of small (on the order of 100-1000 nm) systems of confined electrons called quantum dots. Often kept within semiconductor heterostructures, these systems are small enough that the electrons within them occupy states with discrete energy levels. Two single quantum dots can be placed next to each other so as to form a double dot, with a host of special properties. Such properties can be probed if one can design the semiconductor heterostructure containing the double dot so that experimenters can tune the confinement potential of the double dot. To assist in the testing of heterostructures before their actual construction, we have created a numerical simulation program that calculates the electrostatic potential and charge density for a quantum double dot housed in a semiconductor heterostructure. Relaxation techniques were used to solve Poisson's equation for the heterostructure. The Thomas-Fermi approximation was used to calculate the electron density as a function of the spatially varying electrostatic potential. / (cont.) Certain parameters of the simulation, such as the doping density of the semiconductor material and the electron effective mass, were chosen after trial and error such that the behavior of the simulation matched experimentally observable values, including the electron density within and outside of the quantum double dot region and the depletion voltage. Once the free parameters were chosen, the simulation was used to examine various heterostructure geometries with gates that could tune the confinement potential of the double dot. For example, we analyzed a pincher gate geometry that could split the double dot into two isolated quantum single dots by increasing the potential barrier in the channel connecting the two lobes of the double dot. We discovered that such a tunable dot requires a pincher gate that runs continuously across the bottom of the top gate. We also analyzed how two middle gates., each positioned directly above one of the two lobes of the double dot, can shape the relative sizes of the two connected dots. / by Aaron David Kiyoshi Finck. / S.B.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Includes bibliographical references (p. 54-55). / by James M. Olness. / M.S.