Ultra-long mode-locked Er-droped fibre lasers

The development of ultra-long (UL) cavity (hundreds of meters to several kilometres) mode-locked fibre lasers for the generation of high-energy light pulses with relatively low (sub-megahertz) repetition rates has emerged as a new rapidly advancing area of laser physics. The first demonstration of high pulse energy laser of this type was followed by a number of publications from many research groups on long-cavity Ytterbium and Erbium lasers featuring a variety of configurations with rather different mode-locked operations. The substantial interest to this new approach is stimulated both by non-trivial underlying physics and by the potential of high pulse energy laser sources with unique parameters for a range of applications in industry, bio-medicine, metrology and telecommunications. It is well known, that pulse generation regimes in mode-locked fibre lasers are determined by the intra-cavity balance between the effects of dispersion and non-linearity, and the processes of energy attenuation and amplification. The highest per-pulse energy has been achieved in normal-dispersion UL fibre lasers mode-locked through nonlinear polarization evolution (NPE) for self-modelocking operation. In such lasers are generated the so-called dissipative optical solitons. The uncompensated net normal dispersion in long-cavity resonatorsusually leads to very high chirp and, consequently, to a relatively long duration of generated pulses. This thesis presents the results of research Er-doped ultra-long (more than 1 km cavity length) fibre lasers mode-locked based on NPE. The self-mode-locked erbium-based 3.5-km-long all-fiber laser with the 1.7 µJ pulse energy at a wavelength of 1.55 µm was developed as a part of this research. It has resulted in direct generation of short laser pulses with an ultralow repetition rate of 35.1 kHz. The laser cavity has net normal-dispersion and has been fabricated from commercially-available telecom fibers and optical-fiber elements. Its unconventional linear-ring design with compensation for polarization instability ensures high reliability of the self-mode-locking operation, despite the use of a non polarization-maintaining fibers. The single pulse generation regime in all-fibre erbium mode-locking laser based on NPE with a record cavity length of 25 km was demonstrated. Modelocked lasers with such a long cavity have never been studied before. Our result shows a feasibility of stable mode-locked operation even for an ultra-long cavity length. A new design of fibre laser cavity – “y-configuration”, that offers a range of new functionalities for optimization and stabilization of mode-locked lasing regimes was proposed. This novel cavity configuration has been successfully implemented into a long-cavity normal-dispersion self-mode-locked Er-fibre laser. In particular, it features compensation for polarization instability, suppression of ASE, reduction of pulse duration, prevention of in-cavity wave breaking, and stabilization of the lasing wavelength. This laser along with a specially designed double-pass EDFA have allowed us to demonstrate anenvironmentally stable all-fibre laser system able to deliver sub-nanosecond high-energy pulses with low level of ASE noise

Beyond the quantum limit : a squeezed-light laser in GEO 600

[no abstract

Quantum opto-mechanics with micromirrors

Diese Arbeit beschreibt mehr als vier Jahre an Forschung über die Effekte von Strahlungsdruck von Licht auf makroskopische, mechanische Strukturen. Das System das hier erforscht wird ist ein mechanischer Oszillator der gleichzeitig ein hochreflektierender Spiegel ist und als Teil eines optischen Resonators verwendet wird. Die mechanische Struktur wechselwirkt mit der optischen Mode in der Kavität über die Strahlungsdruckkraft des Lichtes. Sowohl die Dynamik der mechanischen Oszillation als auch die Eigenschaften des Lichtes werden durch diese Wechselwirkung beeinflusst. In unseren Experimenten verwenden wir Werkzeuge der Quantenoptik (wie Homodyndetektion und parametrische Fluoreszenz (= down-conversion)) mit dem Ziel Quantenverhalten der mechanischen Schwerpunktsbewegung zu zeigen. In dieser Dissertation präsentieren wir mehrere Experimente die den Weg zu diesem Ziel ebnen und, wenn gemeinsam durchgeführt, zu der gewünschten Demonstration der makroskopischen, mechanischen Quantenphänomene führen sollten, wie Verschränkung, Teleportation und nicht-klassische Zustände (Stichwort ``Schrödingers Katze''). Das Studium des Quantenverhaltens von makroskopischen Systemen ist ein seit langer Zeit verfolgtes Ziel welches dabei helfen wird einige der zentralen offenen Fragen der modernen Quantenphysik zu beantworten: Warum ist die Welt wie wir sie wahrnehmen klassisch und nicht quantenmechanisch? Gibt es eine Beschränkung in der Größe oder der Masse für Objekte oberhalb der sie sich nicht mehr nach den Gesetzen der Quantenmechanik verhalten können? Ist die Quantentheorie vollständig oder müssen wir sie mit einem Mechanismus wie der Dekohärenz erweitern? Können wir die Quantennatur von makroskopischen Objekten nutzen um zum Beispiel die Messgenauigkeit von klassischen Apparaten zu verbessern? Die Experimente die in dieser Arbeit diskutiert werden inkludieren das erste passive Kühlen eines mechanischen Oszillators mit Hilfe von Strahlunsgdruck in einem kryogenen optischen Resonator überhaupt. Weiters konnten wir ein Experiment durchführen in welchem wir die mechanische Struktur in die Nähe ihres quantenmechanischen Grundzustandes gekühlt haben. Das Kühlen der mechanischen Bewegung ist eine wichtige Voraussetzung um Quantenphänome des mechanischen Oszillators zu beobachten. In einem anderen Experiment haben wir gezeigt, dass wir im Bereich der starken Wechselwirkung des opto-mechanischen Systems arbeiten können. In diesem Bereich ist ein kohärenter Energieaustausch zwischen dem optischen und dem mechanischen System möglich da ihre Wechselwirkungsrate größer ist als ihre individuellen Dekohärenzraten. Dieses Experiment ist ein wichtiger Meilenstein um makroskopisches, mechanisches Quantenverhalten zu zeigen. Zuletzt haben wir in einem Experiment die opto-mechanischen Korrelationen gemessen. Mit Hilfe dieser Korrelationen kann man die aufgrund des Strahlungsdruckes auftretende parametrische Fluoreszenz untersuchen. Dieses Experiment ist so konzipiert, dass man damit in Zukunft Verschränkung zwischen dem optischen und dem mechanischen System sowohl erzeugen, als auch auslesen wird können.This work describes more than four years of research on the effects of the radiation-pressure force of light on macroscopic mechanical structures. The basic system studied here is a mechanical oscillator that is highly reflective and part of an optical resonator. It interacts with the optical cavity mode via the radiation-pressure force. Both the dynamics of the mechanical oscillation and the properties of the light field are modified through this interaction. In our experiments we use quantum optical tools (such as homodyning and down-conversion) with the goal of ultimately showing quantum behavior of the mechanical center of mass motion. In this thesis we present several experiments that pave the way towards this goal and when combined should allow the demonstration of the envisioned quantum phenomena, including entanglement, teleportation and Schr\"odinger cat states. The study of quantum behavior of truly macroscopic systems is a long outstanding goal, which will help to answer some of the most fundamental questions in quantum physics today: Why is the world around us classical and not quantum? Is there a size- or mass-limit to systems for them to behave according to quantum mechanics? Is quantum theory complete or do we have to extend it to include mechanisms such as decoherence? Can we use the quantum nature of macroscopic objects to, for example, improve the measurement precision of classical apparatuses? The experiments discussed in this thesis include the very first passive radiation-pressure cooling of a mechanical oscillator in a cryogenic optical resonator, as well as the experimental demonstration of radiation-pressure cooling close to the mechanical quantum ground state. Cooling of the mechanical motion is an important pre-condition for observing quantum effects of the mechanical oscillator. In another experiment, we have demonstrated that we are able to enter the strong-coupling regime of the optomechanical system a regime where coherent energy exchange between the optical and the mechanical subsystems is possible, as their coupling rate is bigger than their individual decoherence rates. This experiment is an important milestone in showing macroscopic mechanical quantum behavior. Finally, we have performed an experiment where we have measured the optomechanical correlations. The correlations are used for probing radiation-pressure based down-conversion and such an experiment will ultimately allow the generation and detection of entanglement between the optical and the mechanical system

The Design and Construction of a Green Laser and Fabry-Perot Cavity System for Jefferson Lab\u27s Hall A Compton Polarimeter

A high finesse Fabry-Perot cavity with a frequency doubled green laser (CW, 532 nm) have been built and installed in Hall A of Jefferson Lab for high precision Compton polarimetry project in spring of 2010. It provides a high intensity circularly polarized photon target for measuring the polarization of electron beam with energies from 1.0 GeV to 11.0 GeV in a nondestructive manner. The IR beam (CW, 1064 nm) from a Ytterbium doped fiber laser amplifier seeded by a Nd:YAG narrow linewidth NPRO laser is frequency doubled in by a single-pass Periodically Poled Lithium Niobate (PPMgLN) crystal. The maximum achieved green power at 5 W IR pump power was 1.74 W with a total conversion efficiency of 34.8%. The frequency locking of this green light to the cavity resonance frequency is achieved by giving a feedback to Nd:YAG crystal via laser piezoelectric (PZT) actuator by Pound-Drever-Hall (PDH) technique. The data shows the maximum amplification gain of our cavity is about 4,000 with a corresponding maximum intra-cavity power of 3.7 kW. The polarization transfer function has been measured in order to determine the intra-cavity laser polarization within the measurement uncertainty of 0.7%. The PREx experiment at JLab, used this system for the first time and achieved 1.0% precision in electron beam polarization measurement at 1.0 GeV

Recent Progress in Optical Fiber Research

This book presents a comprehensive account of the recent progress in optical fiber research. It consists of four sections with 20 chapters covering the topics of nonlinear and polarisation effects in optical fibers, photonic crystal fibers and new applications for optical fibers. Section 1 reviews nonlinear effects in optical fibers in terms of theoretical analysis, experiments and applications. Section 2 presents polarization mode dispersion, chromatic dispersion and polarization dependent losses in optical fibers, fiber birefringence effects and spun fibers. Section 3 and 4 cover the topics of photonic crystal fibers and a new trend of optical fiber applications. Edited by three scientists with wide knowledge and experience in the field of fiber optics and photonics, the book brings together leading academics and practitioners in a comprehensive and incisive treatment of the subject. This is an essential point of reference for researchers working and teaching in optical fiber technologies, and for industrial users who need to be aware of current developments in optical fiber research areas

Advances in Swept-Wavelength Interferometry for Precision Measurements

Originally developed for radar applications in the 1950s, swept-wavelength interferometry (SWI) at optical wavelengths has been an active area of research for the past thirty years, with applications in fields ranging from fiber optic telecommunications to biomedical imaging. It now forms the basis of several measurement techniques, including optical frequency domain reflectometry (OFDR), swept-source optical coherence tomography (SS-OCT), and frequency-modulated continuous-wave (FMCW) lidar. In this thesis, I present several novel contributions to the field of SWI that include improvements and extensions to the state of the art in SWI for performing precision measurements. The first is a method for accurately monitoring the instantaneous frequency of the tunable source to accommodate nonlinearities in the source tuning characteristics. This work extends the commonly used method incorporating an auxiliary interferometer to the increasingly relevant cases of long interferometer path mismatches and high-speed wavelength tuning. The second contribution enables precision absolute range measurements to within a small fraction of the transform-limited range resolution of the SWI system. This is accomplished through the use of digital filtering in the time domain and phase slope estimation in the frequency domain. Measurements of optical group delay with attosecond-level precision are experimentally demonstrated and applied to measurements of group refractive index and physical thickness. The accuracy of the group refractive index measurement is shown to be on the order of 10-6, while measurements of absolute thicknesses of macroscopic samples are accomplished with accuracy on the order of 10 nm. Furthermore, subnanometer uncertainty for relative thickness measurements can be achieved. For the case of crystalline silicon wafers, the achievable uncertainty is on the same order as the Si-Si bond length, opening the door to potential thickness profiling with single atomic monolayer precision. Thirdly, I demonstrate a novel implementation of SWI in the form of an SS-OCT system for performing quantitative measurements of spatially resolved refractive index contrast. This system relies on the depth-sectioning capability of SWI to isolate Fresnel reflectivity variations at an interface of interest within an optical sample. A motivating application for this quantitative index contrast measurement, volume lithography of photosensitive polymers, is also discussed in detail. This discussion includes the first demonstration of two-dimensional optical waveguide arrays fabricated in photosensitive polymers by means of holographic lithography

Generation and characterization of spatially structured few-photon states of light

The present doctoral dissertation discusses the results of research on the characterization of spatial structure and statistical properties of few-photon states of light generated i.a. with the use of a new source based on multimode atomic memory. The dissertation comprises nine chapters grouped into the following parts: a literature and theoretical introduction, and three main parts providing the experimental results. Part I discusses the characteristics of a scientific complementary metal-oxide semiconductor camera equipped with an image intensifier (I-sCMOS) constructed by our group. We provide theoretical models of saturation of photon-number-resolving detectors which relate qualitatively to our camera. We perform experimental tomography of the I-sCMOS camera and use its results for high-fidelity reconstruction of the original statistics of the impinging light. In Part II we present an atomic memory setup in warm rubidium vapors where the write-in and readout occur due to collective Raman scattering. The memory is able to store information about the spatial structure of light. We describe the experimental setup thoroughly, with particular attention to the filtering system. We characterize multimode Raman scattering and investigate the storage performance of the memory which is limited by diffusional decoherence. We demonstrate spatial correlations between delayed Stokes and anti-Stokes photons. Using the I-sCMOS camera together with an advanced filtering system we observe spatial correlations down to single atomic excitations per memory mode. In Part III we discuss the use of the I-sCMOS camera to observe the Hong-Ou-Mandel two-photon interference with spatial resolution. We study the influence of finite spatial distinguishability of photons on the interference results, which leads us to measurements of the local spatial structure of a single photon. We observe and examine closely the following relatively unexplored phenomena. In Part I we investigate seemingly nonclassical effects in measurements of photon counts statistics on the camera. In Part II we are the first ones to show multimode Raman scattering in atomic memories. Finally, in Part III we describe the first observation of the Hong-Ou-Mandel effect with spatial resolution which is studied further in terms of finite spatial distinguishability of the interfering photons. In this thesis, we present the following novel experimental methodology. We use a new-type of I-sCMOS camera. We implement and perform the reconstruction of photon statistics based on tomographic characterization of the detector. We also build an efficient filtering system for photons generated in atomic memory. Moreover, we create an accurate method of measuring diffusion coefficients in atomic memory. We present our own methods of spatial characterization of the properties of light. Eventually, we introduce an entirely novel method: holographic measurement of the phase structure of a single photon using i.a. a specially developed phase reconstruction algorithm. The presented results fall within the scope of contemporary research in quantum optics and have a number of possible applications, as discussed in the final remarks section.Niniejsza praca doktorska prezentuje wyniki badań poświęconych charakteryzacji struktury przestrzennej i właściwości statystyk kilkufotonowych stanów światła generowanych m.in. z użyciem nowego źródła opartego na wielomodowej pamięci atomowej. Praca składająca się z 9 rozdziałów podzielona jest na wstęp literaturowy i teoretyczny oraz trzy części zawierające merytoryczne wyniki badań. Kolejno w części I prezentujemy i charakteryzujemy skonstruowany układ kamery sCMOS ze wzmacniaczem obrazu (I-sCMOS). Przedstawiamy teoretyczne modele nasycania detektorów rozróżniających liczbę fotonów, które jakościowo odnoszą się do kamery. Przeprowadzamy eksperymentalną tomografię kamery I-sCMOS a jej wyniki wykorzystujemy do wiernej rekonstrukcji pierwotnych statystyk światła padającego na kamerę. W części II prezentujemy układ pamięci atomowej w ciepłych parach rubidu, do której zapis i odczyt odbywa się w wyniku kolektywnego rozpraszania Ramana. Pamięć jest w stanie przechować informacje na temat przestrzennej struktury światła. Dokładnie opisujemy układ doświadczalny, w szczególności pod kątem układu filtrowania. Charakteryzujemy wielomodowe rozpraszanie Ramana oraz badamy zdolność przechowywania pamięci ograniczoną dekoherencją dyfuzyjną. Demonstrujemy korelacje przestrzenne pomiędzy opóźnionymi w czasie fotonami Stokesa i anty-Stokesa. Używając kamery I-sCMOS i zaawansowanego systemu filtrowania obserwujemy korelacje przestrzenne aż do reżimu pojedynczych wzbudzeń atomowych na mod pamięci. W części III wykorzystujemy kamerę I-sCMOS do badania zjawiska interferencji dwufotonowej Hong-Ou-Mandela obserwowanego z rozdzielczością przestrzenną. Studiujemy wpływ skończonej widzialności przestrzennej na wynik interferencji, która służy nam do pomiaru lokalnej struktury przestrzennej pojedynczego fotonu. Zaobserwowaliśmy i zbadaliśmy następujące słabo zbadane zjawiska. W części I badamy pozorne efekty nieklasyczne w statystykach zliczeń fotonów zmierzonych za pomocą kamery. W części II po raz pierwszy pokazujemy wielomodowe rozpraszanie Ramana w pamięciach atomowych. Natomiast w części III prezentujemy pierwszą obserwację efektu Hong-Ou-Mandela z rozdzielczością przestrzenną, którą następnie badamy pod kątem wpływu skończonej rozróżnialności przestrzennej interferujących fotonów. Na potrzeby tej pracy zostały stworzone i opracowane następujące, nowe metodologie badawcze. Stosujemy nowego typu kamerę I-sCMOS, opracowujemy rekonstrukcje statystyk fotonów na podstawie tomograficznej charakteryzacji detektora. Konstruujemy skuteczny układ filtrowania fotonów w pamięci atomowej. Tworzymy nową dokładną metodę pomiaru współczynników dyfuzji w pamięci atomowej. Prezentujemy także własne metody charakteryzacji przestrzennej statystycznych właściwości światła. W końcu, pokazujemy zupełnie nowatorską metodę holograficznego pomiaru struktury fazy pojedynczego fotonu, wykorzystującą m.in. specjalnie stworzony algorytm rekonstrukcji fazy. Zaprezentowane wyniki wpisują się w kontekst współczesnych badań w optyce kwantowej, a także posiadają szereg potencjalnych zastosowań, przedyskutowanych w podsumowaniu pracy