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Schori, Christian

Nom
Schori, Christian
Affiliation principale
Fonction
Post-doc
Identifiants
https://libra.unine.ch/handle/123456789/480

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  • Publication
    Accès libre
    Cross-influence between the two servo-loops of a fully-stabilized Er:fiber optical frequency comb
    (2012-9-28)
    Dolgovskiy, Vladimir 
    ;
    Bucalovic, Nikola 
    ;
    Thomann, Pierre 
    ;
    Schori, Christian 
    ;
    Di Domenico, Gianni 
    ;
    Schilt, Stephane 
    We present a study of the impact of the cross-coupling between the two servo loops used to stabilize the repetition rate frep and the carrier-envelope offset (CEO) frequency fCEO in a commercial Er:fiber frequency comb, based on the combination of experimental measurements and a model of the coupled loops. The developed theoretical model enables us to quantify the influence of the servo-loop coupling on an optical comb line, by simulating the hypothetic case where no coupling would be present. Numerical values for the model were obtained from an extensive characterization of the comb, in terms of frequency noise and dynamic response to a modulation applied to each actuator, for both frep and fCEO. To validate the model, the frequency noise of an optical comb line at 1.56 μm was experimentally measured from the heterodyne beat between the comb and a cavity-stabilized ultranarrow-linewidth laser and showed good agreement with the calculated noise spectrum. The coupling between the two stabilization loops results in a more than 10-fold reduction of the comb mode frequency noise power spectral density in a wide Fourier frequency range.
  • Publication
    Accès libre
    Experimental Validation of a Simple Approximation to Determine the Linewidth of a Laser from its Frequency Noise Spectrum
    (2012-7-2)
    Bucalovic, Nikola 
    ;
    Dolgovskiy, Vladimir 
    ;
    Schori, Christian 
    ;
    Thomann, Pierre 
    ;
    Di Domenico, Gianni 
    ;
    Schilt, Stephane 
    Laser frequency fluctuations can be characterized either comprehensively by the frequency noise spectrum or in a simple but incomplete manner by the laser linewidth. A formal relation exists to calculate the linewidth from the frequency noise spectrum, but it is laborious to apply in practice. We recently proposed a much simpler geometrical approximation applicable to any arbitrary frequency noise spectrum. Here we present an experimental validation of this approximation using laser sources of different spectral characteristics. For each of them, we measured both the frequency noise spectrum to calculate the approximate linewidth and the actual linewidth directly. We observe a very good agreement between the approximate and directly measured linewidths over a broad range of values (from kilohertz to megahertz) and for significantly different laser line shapes.
  • Publication
    Accès libre
    Noise properties of an optical frequency comb from a SESAM-modelocked 1.5 µm solid-state laser stabilized to the 10E-13 level
    (2012-5-26)
    Schilt, Stephane 
    ;
    Dolgovskiy, Vladimir 
    ;
    Bucalovic, Nikola 
    ;
    Schori, Christian 
    ;
    Stumpf, Max
    ;
    Di Domenico, Gianni 
    ;
    Pekarek, Selina
    ;
    Oehler, Andreas
    ;
    Südmeyer, Thomas 
    ;
    Keller, Ursula
    ;
    Thomann, Pierre 
    We present a detailed investigation of the noise properties of an optical frequency comb generated from a femtosecond diode-pumped solid-state laser operating in the 1.5-μm spectral region. The stabilization of the passively mode-locked Er:Yb:glass laser oscillator, referred to as ERGO, is achieved using pump power modulation for the control of the carrier envelope offset (CEO) frequency and by adjusting the laser cavity length for the control of the repetition rate. The stability and the noise of the ERGO comb are characterized in free-running and in phase-locked operation by measuring the noise properties of the CEO, of the repetition rate, and of a comb line at 1558 nm. The comb line is analyzed from the heterodyne beat signal with a cavity-stabilized ultra-narrow-linewidth laser using a frequency discriminator. Two different schemes to stabilize the comb to a radio-frequency (RF) reference are compared. The comb properties (phase noise, frequency stability) are limited in both cases by the RF oscillator used to stabilize the repetition rate, while the contribution of the CEO is negligible at all Fourier frequencies, as a consequence of the low-noise characteristics of the CEO-beat. A linewidth of ≈150 kHz and a fractional frequency instability of 4.2×1E−13 at 1 s are obtained for an optical comb line at 1558 nm. Improved performance is obtained by stabilizing the comb to an optical reference, which is a cavity-stabilized ultra-narrow linewidth laser at 1558 nm. The fractional frequency stability of 8×1E−14 at 1 s, measured in preliminary experiments, is limited by the reference oscillator used in the frequency comparison.
  • Publication
    Accès libre
    Experimental validation of a simple approximation to determine the linewidth of a laser from its frequency noise spectrum
    (2012)
    Bucalovic, Nikola 
    ;
    Dolgovskiy, Vladimir 
    ;
    Schori, Christian 
    ;
    Thomann, Pierre 
    ;
    Di Domenico, Gianni 
    ;
    Schilt, Stephane 
    Laser frequency fluctuations can be characterized either comprehensively by the frequency noise spectrum or in a simple but incomplete manner by the laser linewidth. A formal relation exists to calculate the linewidth from the frequency noise spectrum, but it is laborious to apply in practice. We recently proposed a much simpler geometrical approximation applicable to any arbitrary frequency noise spectrum. Here we present an experimental validation of this approximation using laser sources of different spectral characteristics. For each of them, we measured both the frequency noise spectrum to calculate the approximate linewidth and the actual linewidth directly. We observe a very good agreement between the approximate and directly measured linewidths over a broad range of values (from kilohertz to megahertz) and for significantly different laser line shapes.
  • Publication
    Accès libre
    Frequency discriminators for the characterization of narrow-spectrum heterodyne beat signals: Application to the measurement of a sub-hertz carrier-envelope-offset beat in an optical frequency comb
    (2011)
    Schilt, Stephane 
    ;
    Bucalovic, Nikola 
    ;
    Tombez, Lionel 
    ;
    Dolgovskiy, Vladimir 
    ;
    Schori, Christian 
    ;
    Di Domenico, Gianni 
    ;
    Zaffalon, Michele
    ;
    Thomann, Pierre 
    We describe a radio-frequency (RF) discriminator, or frequency-to-voltage converter, based on a voltage-controlled oscillator phase-locked to the signal under test, which has been developed to analyze the frequency noise properties of an RF signal, e.g., a heterodyne optical beat signal between two lasers or between a laser and an optical frequency comb. We present a detailed characterization of the properties of this discriminator and we compare it to three other commercially available discriminators. Owing to its large linear frequency range of 7 MHz, its bandwidth of 200 kHz and its noise floor below 0.01 Hz2/Hz in a significant part of the spectrum, our frequency discriminator is able to fully characterize the frequency noise of a beat signal with a linewidth ranging from a couple of megahertz down to a few hertz. As an example of application, we present measurements of the frequency noise of the carrier envelope offset beat in a low-noise optical frequency comb.
  • Publication
    Accès libre
    Fully stabilized optical frequency comb with sub-radian CEO phase noise from a SESAM-modelocked 1.5-µm solid-state laser
    (2011)
    Schilt, Stephane 
    ;
    Bucalovic, Nikola 
    ;
    Dolgovskiy, Vladimir 
    ;
    Schori, Christian 
    ;
    Stumpf, Max C.
    ;
    Di Domenico, Gianni 
    ;
    Pekarek, Selina
    ;
    Oehler, Andreas E. H.
    ;
    Südmeyer, Thomas 
    ;
    Keller, Ursula
    ;
    Thomann, Pierre 
    We report the first full stabilization of an optical frequency comb generated from a femtosecond diode-pumped solid-state laser (DPSSL) operating in the 1.5-μm spectral region. The stability of the comb is characterized in free-running and in phase-locked operation by measuring the noise properties of the carrier-envelope offset (CEO) beat, of the repetition rate, and of a comb line at 1558 nm. The high Q-factor of the semiconductor saturable absorber mirror (SESAM)-modelocked 1.5-µm DPSSL results in a low-noise CEO-beat, for which a tight phase lock can be much more easily realized than for a fiber comb. Using a moderate feedback bandwidth of only 5.5 kHz, we achieved a residual integrated phase noise of 0.72 rad rms for the locked CEO, which is one of the smallest values reported for a frequency comb system operating in this spectral region. The fractional frequency stability of the CEO-beat is 20‑fold better than measured in a standard self-referenced commercial fiber comb system and contributes only 10−15 to the optical carrier frequency instability at 1 s averaging time.
  • Publication
    Accès libre
    Light effects in the atomic-motion-induced Ramsey narrowing of dark resonances in wall-coated cells
    (2010)
    Breschi, Evelina
    ;
    Kazakov, G.
    ;
    Schori, Christian 
    ;
    Di Domenico, Gianni 
    ;
    Mileti, Gaetano 
    ;
    Litvinov, A.
    ;
    Matisov, B.
    We report on light shift and broadening in the atomic-motion-induced Ramsey narrowing of dark resonances prepared in alkali-metal vapors contained in wall-coated cells without buffer gas. The atomic-motion-induced Ramsey narrowing is due to the free motion of the polarized atomic spins in and out of the optical interaction region before spin relaxation. As a consequence of this effect, we observe a narrowing of the dark resonance linewidth as well as a reduction of the ground states’ light shift when the volume of the interaction region decreases at constant optical intensity. The results can be intuitively interpreted as a dilution of the intensity effect similar to a pulsed interrogation due to the atomic motion. Finally the influence of this effect on the performance of compact atomic clocks is discussed.
  • Publication
    Accès libre
    Evaluation of the frequency stability of a VCSEL locked to a micro-fabricated Rubidium vapour cell
    (2010)
    Di Francesco, Joab F.
    ;
    Gruet, Florian 
    ;
    Schori, Christian 
    ;
    Affolderbach, Christoph 
    ;
    Matthey-De-L'Endroit, Renaud 
    ;
    Mileti, Gaetano 
    ;
    Salvadé, Y.
    ;
    de Rooij, Nicolaas F.
    ;
    Petremand, Y.
    We present our evaluation of a compact laser system made of a 795 nm VCSEL locked to the Rubidium absorption line of a micro-fabricated absorption cell. The spectrum of the VCSEL was characterised, including its RIN, FM noise and line-width. We optimised the signal-to-noise ratio and determined the frequency shifts versus the cell temperature and the incident optical power. The frequency stability of the laser (Allan deviation) was measured using a high-resolution wavemeter and an ECDL-based reference. Our results show that a fractional instability of ≥ 10-9 may be reached at any timescale between 1 and 100'000 s. The MEMS cell was realised by dispensing the Rubidium in a glass-Silicon preform which was then, sealed by anodic bonding. The overall thickness of the reference cell is 1.5 mm. No buffer gas was added. The potential applications of this compact and low-consumption system range from optical interferometers to basic laser spectroscopy. It is particularly attractive for mobile and space instruments where stable and accurate wavelength references are needed.