182 research outputs found

    Development of a stabilized Ti:Sa frequency comb for frequency comparisons at high stability in the optical region

    Get PDF
    This dissertation describes the development of a self-referenced optical frequency comb (OFC) based on a Ti:Sa femtosecond (fs) laser, to be employed in frequency comparisons between a strontium optical lattice clock and other frequency references, both in the radio-frequency (RF) and in the optical domain. The Ti:Sa mode-locked laser, which employs external fiber broadening (EB) for the generation of octave-spanning spectrum, has been stabilized by locking an OFC tooth to a clock laser with high spectral purity, operating at 698 nm and resonant with the clock transition 1^1S0_0-3^3P0_0 in neutral strontium atoms. The frequency stability of this EB OFC has been tested both in the RF domain by comparison with a high-quality quartz oscillator slaved to the global positioning system (GPS) signal, and in the optical domain with a second stabilized diode laser at 689 nm slaved at long term to the intercombination transition 1^1S0_0-3^3P1_1 in atomic strontium. We perform a frequency noise and intensity-related dynamics characterization of the free-running fs Ti:Sa EB OFC and implement these results for optimizing the phase--lock of the OFC to a Hz-wide 698 nm semiconductor laser. Based on the frequency noise of the beatnote between the clock laser and corresponding EB OFC tooth fb698f_{b698} we expect that the short term frequency stability of the 698 nm clock laser is then transferred to each tooth of the octave-spanning EB OFC. Moreover, the noise transfer processes between the pump laser and the Ti:Sa laser have been studied in detail, both comparing the resulting frequency noise of the EB OFC output spectrum with a single-mode Coherent Verdi V5 and a multi-mode Spectra Physics Millennia Xs 532 nm pump lasers. In particular, in the latter case we demonstrate that the implementation of an additional control loop for the stabilization of carrier-envelope offset (CEO) frequency fCEOf_{CEO} allowed us to stabilize this signal at mHz level, that is compatible with fCEOf_{CEO} stabilization results with the single-mode pump laser case. Moreover, we show that, with our optical standard operated at a wavelength 698 nm the impact of fCEOf_{CEO} frequency noise on the frequency noise of any EB OFC tooth is negligible when compared with the frequency noise of the fb698f_{b698}. Despite the OFCs are used typically for precision frequency measurements, we demonstrate an approach to perform an absolute frequency measurement of unstable frequency by the EB OFC. Most of this thesis is devoted to the EB OFC. However, I also present characteristics and our first stabilization results of the OFC working at quasi octave-spanning regime

    Integrated butt-coupled membrane laser for Indium Phosphide on Silicon platform

    Get PDF
    In this work we present the design and technology development for an integrated butt-coupled membrane laser in the IMOS (Indium Phosphide Membrane On Silicon) platform . Laser is expected to have a small footprint (less than 50 µm 2 ), 1 mA threshold current and a direct modulation frequency of 10 GHz

    In-line fibre-optic laser doppler velocimeter using bragg grating interferometric filters as frequency to intensity transducers

    Get PDF
    Three dimensional complex flows particularly those of turbomachinery present challenges to current measurement technology in terms of restricted optical access, measurement accuracy for the on-axis velocity component, the need to resolve flow turbulence and measurement difficulty from close to surface or intra-channel measurements in rotating machinery. A novel non-intrusive in-line fibre-optic laser Doppler velocimeter is presented specifically for the measurement of the on-axis component of velocity. The measurement principle is based on a Doppler frequency to intensity transducer in the form of a fibre-optic Bragg grating based Fabry-Perot interferometric filter. The filters were fabricated at 514.5 nm but in principle any desired wavelength may be used thus permitting any laser wavelength source to be used. Filters with appropriate features were designed with the aid of the theoretical models based on the coupled mode theory and transfer matrix approach. The argon-ion laser emission wavelength was locked to a corresponding Doppler broadened absorption line of molecular iodine vapour while the Fabry-Perot interferometer phase was controlled in an independent feedback system using digital lock-in amplifiers. The optical frequency was stabilized to within 10 MHz for at least one hour while the phase was controlled to an equivalent of (within) ± 3 MHz in frequency. Both feedback loops utilized custom designed PID electronic circuit controllers. The bandwidth of the filter was tunable by up to 400 MHz, with a resolution of between 0.2 ms'1 and 1 ms"1, and a sensitivity range of between 0.5 [GHz]'1 and 1.7 [GHz]'1. In this technique the filter was tuned to the optical wavelength, rather than tuning the laser wavelength to match the filter. The finished instrument was applied to the measurement of the on-axis component of velocity, of a rotating disc, over an available range of up to ± 42 ms'1, limited only by the maximum velocity of the disc. The detection system was reconfigured for low velocity measurements at twice the sensitivity over a velocity range of ± 7 ms'1. This technique demonstrates a unique contribution to fluid dynamics for the measurement of the traditionally difficult in-line component of velocity.Ph

    A Microscope for Fermi Gases

    Get PDF

    A microscope for Fermi gases

    Get PDF
    Diese Dissertation berichtet über ein neuartiges Quantengasmikroskop, mit dem Vielteilchensysteme von fermionischen Atomen in optischen Gittern untersucht werden. Die einzelplatzaufgelöste Abbildung ultrakalter Gase im Gitter hat mächtige Experimente an bosonischen Vielteilchensystemen ermöglicht. Die Erweiterung dieser Fähigkeit auf Fermigase bietet neue Aussichten, komplexe Phänomene stark korrelierter Systeme zu erforschen, für die numerische Simulationen oft nicht möglich sind. Mit Standardtechniken der Laserkühlung, optischen Fallen und Verdampfungskühlung werden ultrakalte Fermigase von 6Li präpariert und in ein 2D optisches Gitter mit flexibler Geometrie geladen. Die Atomverteilung wird mithilfe eines zweiten, kurzskaligen Gitters eingefroren. Durch Raman-Seitenbandkühlung wird an jedem Atom Fluoreszenz induziert, während seine Position festgehalten wird. Zusammen mit hochauflösender Abbildung erlaubt die Fluoreszenz die Rekonstruktion der ursprünglichen Verteilung mit Einzelplatzauflösung und hoher Genauigkeit. Mithilfe von magnetisch angetriebener Verdampfungskühlung produzieren wir entartete Fermigase mit fast einheitlicher Füllung im ersten Gitter. Dies ermöglicht die ersten mikroskopischen Untersuchungen an einem ultrakalten Gas mit klaren Anzeichen von Fermi-Statistik. Durch die Präparation eines Ensembles spinpolarisierter Fermigase detektieren wir eine Abflachung im Dichteprofil im Zentrum der Wolke, ein Charakteristikum bandisolierender Zustände. In einem Satz von Experimenten weisen wir nach, dass Verluste von Atompaaren an einem Gitterplatz, bedingt durch lichtinduzierte Stöße, umgangen werden. Die Überabtastung des zweiten Gitters erlaubt eine deterministische Trennung der Atompaare in unterschiedliche Gitterplätze. Die Kompression einer dichten Wolke in der Falle vor dem Laden ins Gitter führt zu vielen Doppelbesetzungen von Atomen in unterschiedlichen Bändern, die wir ohne Anzeichen von paarweisen Verlusten abbilden können. Somit erhalten wir die wahre Besetzungsstatistik an jedem Gitterplatz. Mithilfe dieser Besonderheit werten wir die lokale Besetzungsstatistik an einem Ensemble bandisolierenderWolken aus. Im Zentrum bei hoher Füllung sind die Atomzahlfluktuationen um eine Größenordnung unterdrückt, verglichen mit klassischen Gasen, eine Manifestation des Pauliverbots. Die Besetzungswahrscheinlichkeiten werden verwendet, um die lokale Entropie an jedem Gitterplatz zu messen. Eine niedrige Entropie pro Atom bis 0.34kB wird im Zentrum des Bandisolators gefunden. Die Erweiterung der Quantengasmikroskopie auf entartete Fermigase eröffnet neue Möglichkeiten der Quantensimulation stark korrelierter Vielteilchensysteme und kann einzigartige Erkenntnisse über fermionische Systeme im und außerhalb vom Gleichgewicht, Quantenmagnetismus und verschiedene Phasen des Fermi-Hubbard-Modells ergeben.This thesis reports on a novel quantum gas microscope to investigate many-body systems of fermionic atoms in optical lattices. Single-site resolved imaging of ultracold lattice gases has enabled powerful studies of bosonic quantum many-body systems. The extension of this capability to Fermi gases offers new prospects to studying complex phenomena of strongly correlated systems, for which numerical simulations are often out of reach. Using standard techniques of laser cooling, optical trapping, and evaporative cooling, ultracold Fermi gases of 6Li are prepared and loaded into a large-scale 2D optical lattice of flexible geometry. The atomic distribution is frozen using a second, short-scaled lattice, where we perform Raman sideband cooling to induce fluorescence on each atom while maintaining its position. Together with high-resolution imaging, the fluorescence signals allow for reconstructing the initial atom distribution with single-site sensitivity and high fidelity. Magnetically driven evaporative cooling in the plane allows for producing degenerate Fermi gases with almost unity filling in the initial lattice, allowing for the first microscopic studies of ultracold gases with clear signatures of Fermi statistics. By preparing an ensemble of spin-polarised Fermi gases, we detect a flattening of the density profile towards the centre of the cloud, which is a characteristic of a band-insulating state. In one set of experiments, we demonstrate that losses of atom pairs on a single lattice site due to light-assisted collisions are circumvented. The oversampling of the second lattice allows for deterministic separation of the atom pairs into different sites. Compressing a high-density sample in a trap before loading into the lattice leads to many double occupancies of atoms populating different bands, which we can image with no evidence for pairwise losses. We therefore gain direct access to the true number statistics on each lattice site. Using this feature, we can evaluate the local number statistics on an ensemble of band-insulating clouds. In the central region of high filling, the atom number fluctuations are suppressed by an order of magnitude compared to classical gases, which is a manifestation of Pauli blocking. Occupation probabilities are used to measure the local entropy on each individual site. The entropy per atom is found to be as low as 0.34kB in the band-insulating core. The extension of quantum gas microscopy to degenerate Fermi gases opens up new avenues in quantum simulation of strongly correlated many-body systems and can yield unprecedented insight into fermionic systems in and out of equilibrium, quantum magnetism and different phases of the Fermi-Hubbard model
    corecore