Clément Lacroûte

Frequency stability of a wavelength meter and applications to laser frequency stabilization.

Interferometric wavelength meters have attained frequency resolutions down to the megahertz range. In particular, Fizeau interferometers, which have no moving parts, are becoming a popular tool for laser characterization and stabilization. In this paper, we characterize such a wavelength meter using an ultrastable laser in terms of relative frequency instability σ(y)(τ) and demonstrate that it can achieve a short-term instability σ(y)(1s)≈2×10(-10) and a frequency drift of order 10 MHz/day. We use this apparatus to demonstrate frequency control of a near-infrared laser, where a frequency instability below 3×10(-10) from 1 to 2000 s is achieved. Such performance is, for example, adequate for ion trapping and atom cooling experiments.

Design of an ultra-compact reference ULE cavity

This article presents the design and the conception of an ultra-compact Fabry-Perot cavity which will be used to develop an ultra-stable laser. The proposed cavity is composed of a 25 mm long ULE spacer with fused silica mirrors. It leads to an expected fractional frequency stability of 1.5 x 10-15 limited by the thermal noise. The chosen geometry leads to an acceleration relative sensitivity below 10-12 /(m/s2) for all directions.

Compact Yb+ optical atomic clock project: design principle and current status

We present the design of a compact optical clock based on the 2 S 1/2→2 D 3/2 435.5 nm transition in 171 Yb+. The ion trap will be based on a micro-fabricated circuit, with surface electrodes generating a trapping potential to localize a single Yb ion a few hundred μm from the electrodes. We present our trap design as well as simulations of the resulting trapping pseudo-potential. We also present a compact, multi-channel wavelength meter that will permit the frequency stabilization of the cooling, repumping and clear-out lasers at 369.5 nm, 935.2 nm and 638.6 nm needed to cool the ion. We use this wavelength meter to characterize and stabilize the frequency of extended cavity diode lasers at 369.5 nm and 638.6 nm.

Preliminary results of the trapped atom clock on a chip

We present an atomic clock based on the interrogation of magnetically trapped 87Rb atoms. Two photons, in the microwave and radiofrequency domain excite the clock transition. At a magnetic field of 3.23 G the clock transition from |F=1, mF=−1〉 to |F=2, mF=1〉 is 1st order insensitive to magnetic field variations. Long Ramsey interrogation times can thus be achieved, leading to a projected clock stability in the low 10−13 at 1s. We use an atom chip to cool and trap the atoms. A coplanar waveguide has been integrated to the chip to carry the Ramsey interrogation signal, making the physics package as small as (5cm)3. We describe the experimental setup and show preliminary Ramsey fringes of line width 1.25Hz.

Photonic Generation of High Power, Ultrastable Microwave Signals by Vernier Effect in a Femtosecond Laser Frequency Comb

Optical frequency division of an ultrastable laser to the microwave frequency range by an optical frequency comb has allowed the generation of microwave signals with unprecedently high spectral purity and stability. However, the generated microwave signal will suffer from a very low power level if no external optical frequency comb repetition rate multiplication device is used. This paper reports theoretical and experimental studies on the beneficial use of the Vernier effect together with the spectral selective filtering in a double directional coupler add-drop optical fibre ring resonator to increase the comb repetition rate and generate high power microwaves. The studies are focused on two selective filtering aspects: the high rejection of undesirable optical modes of the frequency comb and the transmission of the desirable modes with the lowest possible loss. Moreover, the conservation of the frequency comb stability and linewidth at the resonator output is particularly considered. Accordingly, a fibre ring resonator is designed, fabricated, and characterized, and a technique to stabilize the resonator’s resonance comb is proposed. A significant power gain is achieved for the photonically generated beat note at 10 GHz. Routes to highly improve the performances of such proof-of-concept device are also discussed.

Author Correction: Photonic Generation of High Power, Ultrastable Microwave Signals by Vernier Effect in a Femtosecond Laser Frequency Comb

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Single-ion, transportable optical atomic clocks

For the past 15 years, tremendous progress within the fields of laser stabilization, optical frequency combs and atom cooling and trapping have allowed the realization of optical atomic clocks with unrivaled performances. These instruments can perform frequency comparisons with fractional uncertainties well below , finding applications in fundamental physics tests, relativistic geodesy and time and frequency metrology. Even though most optical clocks are currently laboratory setups, several proposals for using these clocks for field measurements or within an optical clock network have been published, and most of time and frequency metrology institutes have started to develop transportable optical clocks. For the purpose of this special issue, we chose to focus on trapped-ion optical clocks. Even though their short-term fractional frequency stability is impaired by a lower signal-to-noise ratio, they offer a high potential for compactness: trapped ions demand low optical powers and simple loading schemes, and can be trapped in small vacuum chambers. We review recent advances on the clock key components, including ion trap and ultra-stable optical cavity, as well as existing projects and experiments which draw the picture of what future transportable, single-ion optical clocks may resemble.

Toward an ultra-stable laser based on cryogenic silicon cavity

We present the development of an ultra-stable laser based on a Fabry-Perot cavity made from single crystal silicon. This cavity is cooled down to 17 K to reach a nulling of the thermal expansion. Thanks to the high mechanical quality factor of silicon and to the low temperature, the expected thermal noise limited fractional frequency instability is 3 × 10−17.

Compact ultra-stable laser

We present an ultra-stable laser based on a compact Fabry-Perot cavity with a thermal noise limit expected at 2 × 10 15 in trems of fractional frequency stability. The 25 mm long cavity is housed in a cubic vacuum chamber with a volume of about 2.2 L. The measured phase noise is 3 dBrad2/Hz at 1 Hz with a simple optical set-up at 1542 nm.

Characterization of the phase-noise induced by an optical frequency doubler

We report on the characterization, including residual phase noise and fractional frequency instability, of second harmonic generation fiber-coupled periodically poled LiNbO3 (PPLN) waveguides. We observe a residual phase noise as low as −35 dBrad2/Hz at 1 Hz, which makes them compatible with the best up-to-date optical clocks and ultra-stable cavities.