This thesis concerns the study of ultrafast phenomena in semiconductor physics. At the heart of this research is the construction of a colliding-pulse mode-locked (CPM) ring-dye laser. This laser outputs ultrashort optical pulses at a high repetition rate. With a CPM laser, ultrafast semiconductor phenomena may be optically probed. In addition, using this laser to drive photoconductive circuit elements (PCEs), ultrafast electrical pulses can be generated and sampled, allowing novel high-speed devices to be electronically probed. For the measurement of ultrafast time-resolved photoluminescence (PL) a new pump/probe technique called photoluminescence excitation correlation spectroscopy (PECS) was used. The technique itself was investigated both theoretically and experimentally; it was applied to a variety of GaAs samples of interest in the development of high-speed devices.
\r\n\r\nChapter 2 discusses the construction and alignment of the CPM laser, and the autocorrelator used to measure the ultrashort pulses. Although the laser can be run with pulse widths of < 100 fs full-width at half maximum (FWHM), in the work of this thesis, the laser was operated with pulse widths in the range 200 to 400 fs, with a repetition rate of about 120 MHz, and average output power of 10 to 30 mW.
\r\n\r\nIn Chapter 3, the PECS method is investigated both experimentally and theoretically. PECS is a pulse-probe technique that measures the cross-correlation of photo-excited populations. PECS is theoretically investigated using a rate equation model for a simple three-level system consisting of an electron and hole band and a single trap level. The model is examined in the limits of radiative band-to-band dominated recombination, and capture-dominated recombination. In the former limit, no PECS signal is observed. However, in the latter limit, the PECS signal from the band-to-band PL measures the cross-correlation of the excited electron-hole population, and, thus, the electron and hole lifetimes. PECS is experimentally investigated using a case study of PL in semi-insulating (SI) GaAs and In-GaAs. At 77 K, the PECS signal behaves as in the simple model, and an electron-hole lifetime in the range 200 ps is measured. This is much less than the expected radiative lifetime, and therefore the recombination in SI GaAs is capture-dominated. At 5 K, the behavior is more complicated, because of an acceptor, which is un-ionized at 5 K. PECS for the PL band-to-band decay, shows two decay modes: the fast decay (about 100 ps) is due to the saturable decay associated with the acceptor and the slow decay (about 1 ns) is due to bulk capture. The acceptor-related PL also shows complicated behavior: A fast decay is associated with the band-to-acceptor transition, and the donor-acceptor PL saturates, producing a PECS signal that is negative and decays slowly.
\r\n\r\nIn Chapter 4, PECS is used to investigate the large band-to-band PL contrast observed near dislocations in In-alloyed GaAs. It is found that the PL intensity contrast between a bright and dark area correlates with the ratio of the lifetimes measured using PECS in these areas. Thus, the PL intensity contrast is due to the difference in the carrier lifetimes in the different regions. The differences in the behavior of the lifetimes in the bright and dark regions with temperature suggest that the lifetime-governing defects in the two regions are different. Moreover, the defects are deep, and from the shortness of the lifetimes, neither defect is EL2. These results agree with earlier research, which indicated that defects are gettered and generated at these dislocations. The effects of surface recombination on the PL intensity and lifetimes in In-alloyed GaAs are important to the investigations of this chapter. These are investigated in Appendix E, where it is shown that both PL intensity and PECS-measured carrier lifetimes are greatly affected by surface properties and by laser dose and surface preparation. This is thought to be due to the creation of defects, which affects the surface recombination directly, and bends the electronic bands at the surface to affect the surface recombination indirectly. These effects are reduced by minimizing the exposure to the laser and by using a recently developed Na2S surface passivation layer.
\r\n\r\nIn Chapter 5, the carrier lifetime of damaged GaAs is correlated to the cross-correlation of the PCEs fabricated on the same material. Implantation of 200 keV H+ ions at doses in the range of 1011 - 1014 cm-2 is used to damage the GaAs. The carrier lifetimes are inversely proportional to the dose for doses > 1012 cm-2, and do not indicate a saturation of the damage within the range investigated. For the highest dose of 1014 cm-2, a lifetime of 0.6 \u00b1 0.2 ps was measured at 77 K. The PCE cross-correlation decreases less quickly than the lifetime, indicating that some effect other than the lifetime is governing the cross-correlation response speed.
\r\n\r\nFinally, two of the appendices present independent research that is worthy of note. Appendix C presents an attempt to grow HgTe on CdTe using a novel low-temperature Hg-rich melt liquid-phase epitaxial (LPE) growth technique, which involves an in situ cleave. Appendix D presents a program that models the behavior of ultrafast voltage pulses on a dispersive waveguide, which includes a lumped device.
", "doi": "10.7907/9WE7-AP87", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:627", "collection": "thesis", "collection_id": "627", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02132007-141701", "type": "thesis", "title": "Oscillating-Field Current-Drive Schemes for Tokamaks", "author": [ { "family_name": "Schalit", "given_name": "Mark Alan", "clpid": "Schalit-Mark-Alan" } ], "thesis_advisor": [ { "family_name": "Bellan", "given_name": "Paul Murray", "clpid": "Bellan-P-M" } ], "thesis_committee": [ { "family_name": "Bellan", "given_name": "Paul Murray", "orcid": "0000-0002-0886-8782", "clpid": "Bellan-P-M" }, { "family_name": "Cowan", "given_name": "Eugene W.", "clpid": "Cowan-E-W" }, { "family_name": "Keller", "given_name": "Herbert Bishop", "clpid": "Keller-H-B" }, { "family_name": "Corngold", "given_name": "Noel Robert", "clpid": "Corngold-N-R" }, { "family_name": "Saffman", "given_name": "Philip G.", "clpid": "Saffman-P-G" }, { "family_name": "Gould", "given_name": "Roy Walter", "clpid": "Gould-R-W" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "A novel current-drive scheme for steady-state tokamak operation is investigated in which external coils are applied to induce time-periodic fluid-type, fluctuations within the plasma; a nonlinear interaction between these fluctuations results in a time-averaged EMF, which maintains the large-scale magnetic field against Ohmic dissipation. Analytical and numerical modeling of this current-drive scheme is presented for low-frequency schemes (where the nonlinear < u⃗ x b⃗ > EMF is dominant) and for higher-frequency schemes (where the < j⃗ x b⃗ > Hall EMF is dominant). The Hall EMF is dominant at frequencies well above the ion-cyclotron frequency (referred to the strength of the static axial field) - except in the case of the rotamak, where the oscillating electric field is in the same direction as the static axial field.
\r\n\r\nA figure-of-merit for these current-drive schemes is the ratio of the strength of the static axial current to the strength of the oscillating current. This ratio is always much less than unity in all standard MHD calculations. As the electronion collision frequency vanishes, the ratio approaches infinity for the case of the rotamak. The ratio also approaches infinity for the m = 1 analogue of the rotamak - but only in the restrictive case where the static axial field becomes vanishingly small and where the DC magnetic fields are a small fraction of the AC magnetic fields. For the m = 1 analogue, the currents are confined to a skin layer as the axial field becomes very large, with the ratio of DC current strength to the oscillating current strength approaching unity.
\r\n\r\nThe analysis presented here is compared and contrasted with existing theories and to a number of recent experiments.
", "doi": "10.7907/xjrw-pq56", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:10363", "collection": "thesis", "collection_id": "10363", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08042017-160047213", "type": "thesis", "title": "Chiral Perturbation Theory and the Weak Interaction", "author": [ { "family_name": "Bijnens", "given_name": "Johan Lambert", "orcid": "0000-0002-1618-2844", "clpid": "Bijnens-Johan-Lambert" } ], "thesis_advisor": [ { "family_name": "Wise", "given_name": "Mark B.", "orcid": "0000-0002-9125-801X", "clpid": "Wise-M-B" } ], "thesis_committee": [ { "family_name": "Wise", "given_name": "Mark B.", "orcid": "0000-0002-9125-801X", "clpid": "Wise-M-B" }, { "family_name": "Preskill", "given_name": "John P.", "orcid": "0000-0002-2421-4762", "clpid": "Preskill-J" }, { "family_name": "Hitlin", "given_name": "David G.", "orcid": "0000-0003-4028-6982", "clpid": "Hitlin-D-G" }, { "family_name": "Cowan", "given_name": "Eugene W.", "clpid": "Cowan-E-W" } ], "local_group": [ { "literal": "Caltech Theory" }, { "literal": "div_pma" } ], "abstract": "We study the interface between the standard six-quark model and the observed low-energy weak phenomena. The main processes discussed are weak decays of kaons and hyperons. We study first the low-energy effective weak Hamiltonian at the quark level. This is derived using the renormalization group in leading logarithmic approximation.
\r\n\r\nThen some properties of this effective weak Hamiltonian that can be derived using chiral perturbation theory are studied. A review of chiral perturbation theory is included.
\r\n\r\nThis formalism is used to study the relation between K̅0K0 mixing and a \u0394I = 3/2 decay. We find that the logarithmic corrections to this relation are large, making it unreliable. The same formalism is used to discuss a relation between K\u03c0\u03c0, K\u03c0 and K-vacuum matrix elements used in most attempts to compute the K\u03c0\u03c0 matrix element relevant for the \u0394I = 1/2 rule. The domain of validity of this relation is determined.
\r\n\r\nA review of inclusion of baryons in chiral perturbation theory is given and \r\none-loop corrections to the Gell-Mann-Okubo relation; semileptonic hyperon decays and nonleptonic S and P wave decays are calculated. All corrections are small except the nonleptonic P wave decays and one S wave decay. The corrections to the Lee-Sugawara relation are large as a consequence of the latter.
\r\n\r\nSome predictions beyond chiral perturbation theory can be made within the soliton model of baryons. F/D ratios are predicted for hyperon magnetic moments, semileptonic decays and nonleptonic S wave decays in this model.
", "doi": "10.7907/64qa-xw17", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:10408", "collection": "thesis", "collection_id": "10408", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09012017-090944275", "primary_object_url": { "basename": "Suen_WM_1985.pdf", "content": "final", "filesize": 52817792, "license": "other", "mime_type": "application/pdf", "url": "/10408/1/Suen_WM_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Dynamical Electromagnetic Fields Near Black Holes and Multipole Moments of Stationary, General Relativistic Systems", "author": [ { "family_name": "Suen", "given_name": "Wai Mo", "clpid": "Suen-Wai-Mo" } ], "thesis_advisor": [ { "family_name": "Thorne", "given_name": "Kip S.", "orcid": "0000-0002-9475-4318", "clpid": "Thorne-K-S" } ], "thesis_committee": [ { "family_name": "Thorne", "given_name": "Kip S.", "orcid": "0000-0002-9475-4318", "clpid": "Thorne-K-S" }, { "family_name": "Schwarz", "given_name": "John H.", "orcid": "0000-0001-9861-7559", "clpid": "Schwarz-J-H" }, { "family_name": "Wise", "given_name": "Mark B.", "orcid": "0000-0002-9125-801X", "clpid": "Wise-M-B" }, { "family_name": "Cowan", "given_name": "Eugene W.", "clpid": "Cowan-E-W" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "This dissertation contains two works; one of the behavior of dynamical electromagnetic fields in the stationary spacetime generated by a black hole, and the other on the structure of a general stationary vacuum spacetime itself.
\r\n\r\nThe study of electromagnetic field is carried out in terms of the \"membrane formalism\" for black holes; and it is part of a series of papers with the aim of developing that formalism into a complete, self-consistent description of electromagnetic and gravitational fields in a black hole background. Various model problems are presented as aids in understanding the interactions of electromagnetic fields with a black hole, and special attention is paid to the concept of the \"stretched horizon\" which is vital for the membrane formalism.
\r\n\r\nThe second work develops a multipole moment formalism for a general stationary system in general relativity. The multipole moments are defined in terms of a general formal series solution of the stationary Einstein equation, in analogy to multipole moments in the Newtonian theory of gravity. These relativistic moments exhibit many desirable properties and are shown to be useful in studying the interactions between a gravitating body and an external gravitational field. A model calculation applying the formalism to a black hole interacting with an external multipole field shows that the interaction can be understood in terms of \"elastic moduli\" of the black-hole horizon.
", "doi": "10.7907/xayq-7806", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:1371", "collection": "thesis", "collection_id": "1371", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-04132005-100141", "primary_object_url": { "basename": "Brooks_ed_1984.pdf", "content": "final", "filesize": 2739580, "license": "other", "mime_type": "application/pdf", "url": "/1371/1/Brooks_ed_1984.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Non-Perturbative Analysis of Some Simple Field Theories on a Momentum Space Lattice", "author": [ { "family_name": "Brooks", "given_name": "Eugene David, III", "clpid": "Brooks-Eugene-David-III" } ], "thesis_advisor": [ { "family_name": "Bridges", "given_name": "William B.", "clpid": "Bridges-W-B" } ], "thesis_committee": [ { "family_name": "Bridges", "given_name": "William B.", "clpid": "Bridges-W-B" }, { "family_name": "Cowan", "given_name": "Eugene W.", "clpid": "Cowan-E-W" }, { "family_name": "George", "given_name": "Nicholas A.", "clpid": "George-N-A" }, { "family_name": "Papas", "given_name": "Charles Herach", "clpid": "Papas-C-H" }, { "family_name": "Psaltis", "given_name": "Demetri", "orcid": "0000-0003-4684-8800", "clpid": "Psaltis-D" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "In this work, we develop a new technique for the numerical study of quantum field theory. The procedure, borrowed from non-relativistic quantum mechanics, is that of finding the eigenvalues of a finite Hamiltonian matrix. The matrix is created by evaluating the matrix elements of the Hamiltonian operator on a finite basis of states. The eigenvalues and eigenvectors of the finite dimensional matrix become an accurate approximation to those of the physical system as the finite basis of states is extended to become more complete.
\r\n\r\nWe study a model of scalars coupled to fermions in 0+1 dimensions as a simple field theory to consider in the course of developing the technique. We find in the course of studying this model a change of basis which diagonalizes the Hamiltonian in the large coupling limit. The importance of this transformation is that it can be generalized to higher dimensional field theories involving a trilinear coupling between a Bose and a Fermi field.
\r\n\r\nHaving developed the numerical and analytical techniques, we consider a Fermi field coupled to a Bose field in 1+1 dimensions with the Yukawa coupling \u03bb\u03a8\u03a8\u03a8. We extend the large coupling limit basis of the 0+1 dimensional model to this case using a Bogoliubov transformation on the fermions. Although we do not use this basis in the numerical work due to its complexity, it provides a handle on the behavior of the system in the large coupling limit. In this model we consider the effects of renormalization and the generation of bound states.
", "doi": "10.7907/333S-XC47", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:10410", "collection": "thesis", "collection_id": "10410", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09012017-133647841", "type": "thesis", "title": "Black-Hole Electrodynamics", "author": [ { "family_name": "Macdonald", "given_name": "Douglas Alan", "clpid": "Macdonald-Douglas-Alan" } ], "thesis_advisor": [ { "family_name": "Thorne", "given_name": "Kip S.", "orcid": "0000-0002-9475-4318", "clpid": "Thorne-K-S" } ], "thesis_committee": [ { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Cowan", "given_name": "Eugene W.", "clpid": "Cowan-E-W" }, { "family_name": "Wise", "given_name": "Mark B.", "orcid": "0000-0002-9125-801X", "clpid": "Wise-M-B" }, { "family_name": "Thorne", "given_name": "Kip S.", "orcid": "0000-0002-9475-4318", "clpid": "Thorne-K-S" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "This dissertation considers several aspects of the structure and dynamics of electromagnetic fields around black holes. The four-dimensional, covariant laws of electrodynamics are reformulated in a 3 + 1 (space+time) language in which the key quantities are three-dimensional vectors lying in hypersurfaces of a constant global time t. This formulation is applied to the Blandford-Znajek model of power generation in quasars, which consists of a supermassive black hole surrounded by an accretion disk that holds a magnetic field on the hole, with the rotational energy and angular momentum of the hole and disk being extracted by electromagnetic torques. The 3 + 1 formalism allows the theory of stationary, axisymmetric black holes and their magnetospheres to be couched in an \"absolute-space/universal-time\" language very similar to the flat\u00ad spacetime theory of pulsar electrodynamics; and this similarity allows fiat-space pulsar concepts to be extended to curved-space black holes. The Blandford\u00ad-Znajek quasar model is reformulated in terms of a DC circuit-theory analysis, and action principles describing the overall structure of the magnetosphere and the field distribution on the horizon are developed. A general prescription for constructing global models of force-free magnetospheres is developed and this prescription is used to generate numerical models of black-hole magneto\u00adspheres for a variety of field configurations and black-hole angular velocities. The electromagnetic boundary conditions at the horizon of a black hole are described in terms of a recently developed \"membrane viewpoint\". The necess\u00adity and efficacy of using a \"stretched horizon\" in the membrane viewpoint is discussed, and is illustrated by two simple dynamical problems involving electromagnetic fields near black-hole horizons.
", "doi": "10.7907/vv78-at49", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:4489", "collection": "thesis", "collection_id": "4489", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11102005-102554", "primary_object_url": { "basename": "Abushagur_ma_1984.pdf", "content": "final", "filesize": 4187857, "license": "other", "mime_type": "application/pdf", "url": "/4489/1/Abushagur_ma_1984.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Scattering of Light from Large Cylinders", "author": [ { "family_name": "Abushagur", "given_name": "Mustafa A. G.", "clpid": "Abushagur-Mustafa-A-G" } ], "thesis_advisor": [ { "family_name": "Bridges", "given_name": "William B.", "clpid": "Bridges-W-B" } ], "thesis_committee": [ { "family_name": "Cowan", "given_name": "Eugene W.", "clpid": "Cowan-E-W" }, { "family_name": "George", "given_name": "Nicholas A.", "clpid": "George-N-A" }, { "family_name": "Papas", "given_name": "Charles Herach", "clpid": "Papas-C-H" }, { "family_name": "Psaltis", "given_name": "Demetri", "orcid": "0000-0003-4684-8800", "clpid": "Psaltis-D" }, { "family_name": "Bridges", "given_name": "William B.", "clpid": "Bridges-W-B" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Scattering of a plane electromagnetic wave from circular conducting and dielectric cylinders is analyzed. Both polarizations of the incident electric field, parallel and normal to the axis of the cylinder, are considered. The study of the rigorous solutions gives an insightful understanding of the scattered field and its dependence on the material of the cylinder, the polarizations of the incident field, and the three dimensionality of the object which usually are not considered in Fourier optics. It is shown that a combination of Fourier optics and ray theory can give good approximations for the scattered field from both conducting and dielectric cylinders. It is shown that the scattered pattern from a conducting cylinder consists of a main lobe and a number of side lobes. The spacing between the side lobes decreases as ka increases, where k is the wave number of the incident field and a the radius of the cylinder. It is found that for a certain conducting cylinder the side lobes terminate in a smaller scattering angle when the incident field is polarized parallel to the axis than when the incident field is polarized normal to the axis of the cylinder. The surface current density in the shadow region is found to be larger for the normal polarization case than for the parallel polarization case. The pattern of the scattered field from a dielectric cylinder has fringes all around the cylinder. The contrast of the fringes for the dielectric cylinder is much larger when the polarization of the incident field is parallel to the axis than that when the polarization is normal to the axis. The backscattered field of the dielectric cylinder has a peak which depends in its position on the refractive-index of the cylinder for the parallel polarization case. The fine structure of the scattering by a dielectric cylinder is studied. It is shown that the dielectric cylinder has resonant frequencies which depend on the radius and refractive-index of the cylinder. It is found that there are significant differences in the shape of the scattered pattern depending on whether the cylinder is at-resonance or at off-resonance. Experimental investigations are carried out to verify the theory derived in this study and it is found that both theory and experiments are in good agreement.
", "doi": "10.7907/akkw-r889", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" } ]