Physics Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2800
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Item NONLINEAR PROPAGATION OF ORBITAL ANGULAR MOMENTUM LIGHT IN TURBULENCE AND FIBER(2024) Elder, Henry; Sprangle, Phillip; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Light that carries orbital angular momentum (OAM), also referred to as optical vortices or twisted light, is characterized by a helical or twisted wavefront ∝exp[imφ]. In contrast to spin angular momentum (SAM), where photons are limited to two states, OAM allows for, in principle, an infinite set of spatially orthogonal states. OAM-carrying light has found applications ranging from quantum key distribution in free space and guided-wave communication systems, particle trapping and optical tweezers, nanoscopy, and remote sensing. Understanding how OAM light propagates through complex environments, and how to efficiently generate particular OAM states, is critical for any such application. In the first part of this dissertation, we describe how OAM light propagates through a turbulent atmosphere. We build analytic models which describe (1) the OAM mode mixing caused by turbulence, (2) the evolution of short, high-power OAM pulses undergoing the effects of self-phase modulation (SPM) and group velocity dispersion (GVD), and (3) the evolution of high-power Gaussian pulses including SPM, GVD, and turbulence. The models are validated against both experimental data and nonlinear, turbulent pulse propagation simulation programs, the latter of which we have made freely available. We also explore how self-focusing can minimize certain deleterious effects of turbulence for OAM light. The second part of this dissertation considers nonlinear effects of OAM light propagating in azimuthally symmetric waveguides. Such waveguides have so-called spin-orbit (SO) modes, which are quantized based on their total angular momentum (TAM). We develop a generalized theory of four wave mixing-based parametric amplification of SO modes and show that these processes conserve TAM, but under certain circumstances can be taken to conserve SAM and OAM independently. Our theory is validated against a nonlinear multimode beam propagation simulation program which we developed and, again, have made freely available.Item Spatiotemporal Optical Vortices(2023) Hancock, Scott; Milchberg, Howard; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Light beams carrying orbital angular momentum (OAM) have become a mainstay of optical science and technology. In these beams, well-known examples of which are the Laguerre-Gaussian (LG_pm ) and Bessel-Gaussian (BG_m ) beams, the OAM vector points parallel or anti-parallel to propagation, and is associated with a phase winding 2πm in the plane transverse to the propagation direction, where integer m is the winding order or the “topological charge”. Such beams can be monochromatic.Recently, our group discovered a new type of OAM structure that naturally emerges from nonlinear self-focusing, which we dubbed the spatio-temporal optical vortex (STOV). Here, the phase winding exists in a spatiotemporal plane, with the OAM pointing transverse to propagation. In this dissertation, we extend the generation of STOV-carrying pulses to the linear regime, demonstrating their generation using a 4f pulse shaper and measuring their free-space propagation using a new ultrafast single-shot space- and time-resolving diagnostic, TG-SSSI (transient-grating single-shot supercontinuum spectral interferometry). We then demonstrate that transverse OAM is a property of photons by experimentally confirming the conservation of transverse OAM in second harmonic generation. Because the field of STOVs is so new, a first principles theory for their transverse OAM was lacking. We developed such a theory for transverse OAM that predicts half integer values of OAM and the existence of a STOV polariton in dispersive media. The surprise of half-integer OAM values launched a debate in the OAM community, which has been resolved in favor of our theory by our most recent experiments. These explore how phase and amplitude perturbations can impart spatiotemporal torques to light. We find that transverse OAM can be imparted to light pulses only for (1) sufficiently fast transient phase perturbations or (2) energy removal from a pulse already possessing transverse OAM.Item Experiments with Frequency Converted Photons from a Trapped Atomic Ion(2022) Hannegan, John Michael; Quraishi, Qudsia; Linke, Norbert; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Trapped atomic ions excel as local quantum information processing nodes, given their long qubit coherence times combined with high fidelity single-qubit and multi-qubit gate operations. Trapped ion systems also readily emit photons as flying qubits, making efforts towards construction of large-scale and long-distance trapped-ion-based quantum networks very appealing. Two-node trapped-ion quantum networks have demonstrated a desirable combination of high-rate and high-fidelity remote entanglement generation, but these networks have been limited to only a few meters in length. This limitation is primarily due to large fiber-optic propagation losses experienced by the ultraviolet and visible photons typically emitted by trapped ions. These wavelengths are also incompatible with existing telecommunications technology and infrastructure, as well as being incompatible with many other emerging quantum technologies designed for useful tasks such as single photon storage, measurement, and routing, limiting the scalability of ion-based networks. In this thesis, I discuss a series of experiments where we introduce quantum frequency conversion to convert single photons at 493 nm, produced by and entangled with a single trapped $^{138}$Ba$^+$ ion, to near infrared wavelengths for reduced network transmission losses and improved quantum networking capabilities. This work is the first-ever to frequency convert Ba$^+$ photons, being one of three nearly concurrent demonstrations of frequency converted photons from any trapped ion. After discussing our experimental techniques and laboratory setup, I first showcase our quantum frequency converters that convert ion-produced single photons to both 780 nm and 1534 nm for improved quantum networking range, whilst preserving the photons' quantum properties. Following this, I present two hybrid quantum networking experiments where we interact converted ion-photons near 780 nm with neutral $^{87}$Rb systems. In the initial experiment, we observe, for the first time, interactions between converted ion-photons and neutral Rb vapor via slow light. The following experiment is a multi-laboratory project where we observe Hong-Ou-Mandel interference between converted ion-photons and photons produced by an ensemble of neutral Rb atoms, where notably these sources are located in different buildings and are connected and synchronized via optical fiber. Finally, I describe an experiment in which we verify entanglement between a $^{138}$Ba$^+$ ion and converted photons near 780 nm. These results are critical steps towards producing remote entanglement between trapped ion and neutral atom quantum networking nodes. Motivated by these experimental results, I conclude by presenting a theoretical hybrid-networking architecture where neutral-atomic based nondestructive single photon measurement and storage can be integrated into a long-distance trapped-ion based quantum network to potentially improve remote entanglement rates.Item Towards Low-frequency Squeezed Light and Its Applications with Four-wave Mixing in Rubidium Vapor(2020) Wu, Meng-Chang; Lett, Paul D.; Rolston, Steven L.; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We study a variety of mechanisms that introduce noise into squeezed light generated by a four-wave mixing (4WM) process in Rb vapor. The noise from the seeding beam itself is a general noise that appears in any squeezed light generated from a seeding process. This noise dominates in the squeezed light at acoustic and lower measurement frequencies. A second excess noise source is observed in the twin beams pumped by either a diode laser system or a Ti:sapphire laser system. This excess noise is much stronger in the diode laser systems. It is present in the twin beams at measurement frequencies when the 4WM gain is reduced toward unity. Most of this excess noise can be removed with a dual-seeded 4WM scheme. A third noise source we examine is from a two-beam coupling that degrades the squeezing of the dual-seeded 4WM process at low frequencies of the order of the atomic transition linewidth. This noise can be avoided by seeding skew rays in the 4WM gain region. This gives us an insight to solve this "cross talk" problem by imaging the source in the 4WM gain region. In addition to studying noise sources, we propose a gain-independent calibration scheme that relies on higher order correlation function for the absolute calibration of photodiodes. Having low frequency squeezing is really important if we record quantum images with a CCD camera, which has a slow shutter speed. Also, it's been very difficult for people to get low-frequency squeezing. We obtain a record level of low-frequency squeezing using a simple dual-seeding technique. With this study of noise sources we are closer to having a portable quantum light source using diode lasers.Item Energy Deposition in Femtosecond Filamentation: Measurements and Applications(2017) Rosenthal, Eric Wieslander; Milchberg, Howard M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Femtosecond filamentation is a nonlinear optical propagation regime of high peak power ultrashort laser pulses characterized by an extended and narrow core region of high intensity whose length greatly exceeds the Rayleigh range corresponding to the core diameter. Providing that a threshold power is exceeded, filamentation can occur in all transparent gaseous, liquid and solid media. In air, filamentation has found a variety of uses, including the triggering of electric discharges, spectral broadening and compression of ultrashort laser pulses, coherent supercontinuum generation, filament-induced breakdown spectroscopy, generation of THz radiation, and the generation of air waveguides. Several of these applications depend on the deposition of energy in the atmosphere by the filament. The main channels for this deposition are the plasma generated in the filament core by the intense laser field and the rotational excitation of nitrogen and oxygen molecules. The ultrafast deposition acts as a delta function-like pressure source to drive a hydrodynamic response in the air. This thesis experimentally demonstrates two applications of the filament-driven hydrodynamic response. One application is the ‘air waveguide’, which is shown to either guide a separately injected laser pulse, or act as a remote collection optic for weak optical signals. The other application is the high voltage breakdown of air, where the effect of filament-induced plasmas and hydrodynamic response on the breakdown dynamics is elucidated in detail. In all of these experiments, it is important to understand quantitatively the laser energy absorption; detailed absorption experiments were performed as a function of laser parameters. Finally, as check on simulations of filament propagation and energy deposition, we measured the axially resolved energy deposition of a filament; in the simulations, this profile is quite sensitive to the choice of the nonlinear index of refraction (n2). We found that using our measured values of n2 in the propagation simulations results in an excellent fit to the measured energy deposition profiles.