Extensive development of optical frequency combs, broadband coherent light sources with equidistant narrow spectral lines, in the near-infrared and visible has provided numerous opportunities in many fields, including frequency metrology, astronomy, attosecond sciences, and spectroscopy. The quest for extension of frequency comb techniques to the mid-infrared -- the molecular fingerprint spectral region -- continues with the promise of significant improvements in various applications related to molecular spectroscopy. This dissertation presents the results of a novel method for producing broadband mid-infrared frequency combs through sub-harmonic generation from commercially available near-infrared sources. Sub-harmonic generation occurs in a degenerate optical parametric oscillator (OPO) with salient features of (i) simplicity of the setup, (ii) low (100 mW) pump power requirement, (iii) potential for high ( 90%) conversion eciency and (vi) intrinsic phase and frequency locking to the pump. The resulting mid-infrared frequency comb is then broadened through supercontinuum generation by in-situ tapering of a chalcogenide fiber to cover the spectral range from 2.2 to 5 microns, desirable for molecular spectroscopy. Apart from its effectiveness in extension of the existing near-infrared frequency combs to the mid-infrared, sub-harmonic generation paves the way for quantum optical experiments in the frequency comb regime, because of the intriguing quantum behavior of OPOs at degeneracy. The coherence properties of such a frequency comb OPO are discussed, and the results of a novel all-optical post-precessing-free quantum random number generator are presented.

Over the last few years, there has been a convergence between the fields of ultrafast science, nonlinear optics, optical frequency metrology, and precision laser spectroscopy. These fields have been developing largely independently since the birth of the laser, reaching remarkable levels of performance. On the ultrafast frontier, pulses of only a few cycles long have been produced, while in optical spectroscopy, the precision and resolution have reached one part in Although these two achievements appear to be completely disconnected, advances in nonlinear optics provided the essential link between them. The resulting convergence has enabled unprecedented advances in the control of the electric field of the pulses produced by femtosecond mode-locked lasers. The corresponding spectrum consists of a comb of sharp spectral lines with well-defined frequencies. These new techniques and capabilities are generally known as “femtosecond comb technology. ” They have had dramatic impact on the diverse fields of precision measurement and extreme nonlinear optical physics. The historical background for these developments is provided in the Foreword by two of the pioneers of laser spectroscopy, John Hall and Theodor Hänsch. Indeed the developments described in this book were foreshadowed by Hänsch’s early work in the 1970s when he used picosecond pulses to demonstrate the connection between the time and frequency domains in laser spectroscopy. This work complemented the advances in precision laser stabilization developed by Hall.

An important guide to the major techniques for generating coherent light in the mid-infrared region of the spectrum Laser-based Mid-infrared Sources and Applications gives a comprehensive overview of the existing methods for generating coherent light in the important yet difficult-to-reach mid-infrared region of the spectrum (2–20 μm) and their applications. The book describes major approaches for mid-infrared light generation including ion-doped solid-state lasers, fiber lasers, semiconductor lasers, and laser sources based on nonlinear optical frequency conversion, and reviews a range of applications: spectral recognition of molecules and trace gas sensing, biomedical and military applications, high-field physics and attoscience, and others. Every chapter starts with the fundamentals for a given technique that enables self-directed study, while extensive references help conduct deeper research. Laser-based Mid-infrared Sources and Applications provides up-to-date information on the state-of the art mid-infrared sources, discusses in detail the advancements made over the last two decades such as microresonators and interband cascade lasers, and explores novel approaches that are currently subjects of intense research such as supercontinuum and frequency combs generation. This important book: • Explains the fundamental principles and major techniques for coherent mid-infrared light generation • Discusses recent advancements and current cutting-edge research in the field • Highlights important biomedical, environmental, and military applications Written for researchers, academics, students, and engineers from different disciplines, the book helps navigate the rapidly expanding field of mid-infrared laser-based technologies.

An optical frequency comb (OFC) is a light source whose spectrum comprises of several sharp, equally spaced lines. They were originally developed more than two decades ago to simplify the measurement of optical frequencies in terms of precise atomic standards. OFC technology has progressed remarkably since the first demonstration and OFCs are now the cornerstones of modern-day frequency metrology, precision spectroscopy, astronomical observations, ultrafast optics and quantum information. While the current bulk mode-locked laser frequency comb has had great success in extending the scientific frontier, its use in real-world applications beyond the laboratory setting remains an unsolved challenge due to the relatively large size, weight and power consumption. Recently microresonator-based frequency combs have emerged as a candidate solution with chip-scale implementation and scalability. Microresonator platforms for comb generation are the subject of significant research efforts, which are primarily focused into three areas - comb stabilization, control over comb state generated and evolution paths and study of the comb formation dynamics. In this dissertation we focus on each of these three different areas. First, a novel internal phase-stabilized frequency microcomb that does not require nonlinear second-third harmonic generation nor optical external frequency references is demonstrated. It is shown that the optical frequency can be stabilized by control of two internally accessible parameters: an intrinsic comb offset and the comb spacing. Second, direct electrical control of microresonator parameters is achieved by coupling the gate-tunable optical conductivity of graphene to a silicon nitride photonic microresonator, and modulating its second- and higher-order chromatic dispersions by altering the Fermi level. This is then used to produce charge-tunable primary comb lines from 2.3 terahertz to 7.2 terahertz, coherent Kerr frequency combs, controllable Cherenkov radiation and controllable soliton states, all in a single microcavity. In addition, voltage-tunable transitions between soliton crystal states with defects with defects is demonstrated and mapped via ultrafast second-harmonic optical autocorrelation. Finally, novel ultrafast spectral and temporal measurement techniques are characterized and used to directly capture snapshots of the microresonator field at resolutions of less than 1 ps. These methods are applied to study spectral energy transfer, complex breathing dynamics, collective motion in soliton ensembles and the occurrence of extreme events from a chaotic background.

High harmonic generation, two-state quantum system, extreme-ultraviolet frequency comb. - Erzeugung hoher Harmonischer, Zweizustandssystem, Extrem-Ultraviolett Frequenzkamm

Enhancement cavities are passive optical resonators in which continuous-wave laser radiation or pulses of a frequency comb are coherently overlapped, allowing for a power and intensity scaling of up to several orders of magnitude. A prominent application is the table-top generation of bright, laser-like radiation in spectral regions where direct laser action is inefficient or not available at all, via intracavity nonlinear optical processes. However, to exploit the full capacity of this technique further progress is needed. This thesis covers central problems of enhancement cavities, such as finding limitations in scaling the circulating power, measuring cavity parameters with high accuracy, tailoring transverse modes and coupling out radiation generated in the cavity. Unprecedented intracavity laser powers were demonstrated, surpassing previous results by an order of magnitude. As an application, harmonics of the fundamental 1040-nm radiation up to the 21st order are generated. Besides reporting these fine experimental results, the thesis provides an excellent introduction into the physics of enhancement cavities, supported by more than 140 references.

Volume 55 of the Advances in Atomic, Molecular, and Optical Physics Series contains seven contributions, covering a diversity of subject areas in atomic, molecular and optical physics. In their contribution, Stowe, Thorpe, Pe'er, Ye, Stalnaker, Gerginov, and Diddams explore recent developments in direct frequency comb spectroscopy. Precise phase coherence among successive ultrashort pulses of a frequency comb allows one to probe fast dynamics in the time domain and high-resolution structural information in the frequency domain for both atoms and molecules. The authors provide a detailed review of some of the current applications that exploit the unique features of frequency comb spectroscopy and discuss its future directions. Yurvsky, Olshanii and Weiss review theory and experiment of elongated atom traps that confine ultracold gases in a quasi-one-dimensional regime. Under certain conditions, these quasi-one-dimensional gases are well-described by integrable one-dimensional many-body models with exact quantum solutions. Thermodynamic and correlation properties of one such model that has been experimentally realized are reviewed. DePaola, Morgenstein and Andersen discuss magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS), exploring collisions between a projectile and target resulting in charged target fragments. MOTRIMS combines the technology of laser cooling and trapping of target atoms with the momentum analysis of the charged fragments that recoil from the target. The authors review the different MOTRIMS experimental approaches and the spectroscopic and collisional investigations performed so far. Safronova and Johnson give an overview of atomic many-body perturbation theory and discuss why extensions of the theory are needed. They present "all-order results based on a linearized version of coupled cluster expansions and apply the theory to calculations of energies, transition matrix elements and hyperfine constants. Another contribution on atomic theory, authored by Fischer, explores the advantages of expanding the atomic radial wave functions in a B-spline basis. The differential equations are replaced by non-linear systems of equations and the problems of orthogonality requirements can be dealt with using projection operators. Electron-ion collisional processes are analyzed by Mueller, including descriptions of the experimental techniques needed to obtain cross section data and typical values for these cross sections. The present status of the field is discussed in relation to the detailed cross sections and rate coefficients that are needed for understanding laboratory or astrophysical plasmas. Finally, Duan and Monroe review ways to achieve scalable and robust quantum communication, state engineering, and quantum computation. Using radiation and atoms, ions, or atomic ensembles, they show that they can construct scalable quantum networks that are inherently insensitive to noise. Progress in experimental realization of their proposals is outlined. - International experts - Comprehensive articles - New developments

Optical frequency combs are an exciting area of research with applications in Spectroscopy, optical sensing and telecommunications and in addition they have revolutionized the optical clock. Octave spanning frequency combs have been recently demonstrated using Microresonators. Made from a transparent material, these devices have spherical or toroidal shape and are typically between tens and hundreds of micrometers in size. The light is coupled in through a prism or fibre taper using evanescent wave coupling and circulates the cavity in highly confined whispering gallery modes. Due to the small modal cross section and long photon lifetimes there is a low threshold for nonlinear interaction. Researchers envisage these devices being used for low power microchip scale frequency comb sources in photonic devices. There has been much work on the experimental side of Microresonators, but little in the way of modelling, in particular the interesting nonlinear optical properties of these devices. This thesis describes a new method for modelling microresonator frequency combs, which reduces computational time compared to existing approaches. Two numerical simulation methods, the Newton-Raphson and split step Fourier, are chosen for their suitability to the study of steady state and dynamic regimes respectively. Simulations were performed using code written in MATLAB. We were able to simulate frequency combs with spans exceeding one octave of the spectral domain and containing over 1000 spectral modes, more than twice the number of modes than in any previously published study. The comb spectra were found to be in good agreement with experimental combs published by other researchers. Finally, some inroads were made to a numerical study of comb versatility.

This is the latest volume in the series of proceedings from the biannual International Conference on Laser Spectroscopy, one of the leading conferences in the field. Over its 34-year history, this conference series has been a forum for the announcement of many new developments in laser physics and laser spectroscopy and more recently laser cooling of atoms and quantum information processing. The proceedings include contributions from the invited speakers and a selection of contributed papers.A particular theme for this volume is precision measurements. Motivated by the untapped potential for vast improvements in accuracy offered by atomic systems, this subject has advanced tremendously in recent years by new developments in laser technology. This has been recognized by the 2005 Nobel Prize in Physics awarded to two of the pioneers in the field and contributors to these proceedings, J L Hall and T W Hänsch.The other main theme of the proceedings is cold atoms and quantum degenerate gases. This conference marked the 10th anniversary of the first announcement of an atomic Bose-Einstein Condensate at the 12th International Conference on Laser Spectroscopy with a contribution from Nobel Laureate Eric Cornell.

This book discusses the latest research ideas with application to frequency standards (e.g. optical clocks) and assesses ideas from previous symposia which have undergone critical analysis.