Rodolphe Le Targat

Optical to microwave clock frequency ratios with a nearly continuous strontium optical lattice clock

Optical lattice clocks are at the forefront of frequency metrology. Both the instability and systematic uncertainty of these clocks have been reported to be two orders of magnitude smaller than the best microwave clocks. For this reason, a redefinition of the SI second based on optical clocks seems possible in the near future. However, the operation of optical lattice clocks has not yet reached the reliability that microwave clocks have achieved so far. In this paper, we report on the operation of a strontium optical lattice clock that spans several weeks, with more than 80% uptime. We make use of this long integration time to demonstrate a reproducible measurement of frequency ratios between the strontium clock transition and microwave Cs primary and Rb secondary frequency standards.

Accurate optical lattice clock with 87Sr atoms.

We report a frequency measurement of the 1S0-3P0 transition of 87Sr atoms in an optical lattice clock. The frequency is determined to be 429 228 004 229 879(5) Hz with a fractional uncertainty that is comparable to state-of-the-art optical clocks with neutral atoms in free fall. The two previous measurements of this transition were found to disagree by about 2 x 10(-13), i.e., almost 4 times the combined error bar and 4 to 5 orders of magnitude larger than the claimed ultimate accuracy of this new type of clocks. Our measurement is in agreement with one of these two values and essentially resolves this discrepancy.

Hyperpolarizability Effects in a Sr Optical Lattice Clock

We report the observation of a higher-order frequency shift due to the trapping field in a (87)Sr optical lattice clock. We show that, at the magic wavelength of the lattice, where the first-order term cancels, the higher-order shift will not constitute a limitation to the fractional accuracy of the clock at a level of 10(-18). This result is achieved by operating the clock at very high trapping intensity up to 400 kW/cm(2) and by a specific study of the effect of the two two-photon transitions near the magic wavelength.

Accuracy evaluation of an optical lattice clock with bosonic atoms

We report what we believe to be the first accuracy evaluation of an optical lattice clock based on the S01-->P03 transition of an alkaline earth boson, namely, Sr88 atoms. This transition has been enabled by using a static coupling magnetic field. The clock frequency is determined to be 429228066418009(32)Hz. The isotopic shift between Sr87 and Sr88 is 62188135Hz with fractional uncertainty 5x10(-7). We discuss the necessary conditions to reach a clock accuracy of 10(-17) or less by using this scheme.

Optical Lattice Clock with Spin-polarized 87Sr Atoms

We report on the evaluation of an optical lattice clock using fermionic 87Sr. The measured frequency of the 1S0 → 3P0 clock transition is 429 228 004 229 873.7Hz with a fractional acuracy of 2.6 × 10-15. This evaluation is performed on mF = ±9/2 spin-polarized atoms. This technique also enables to evaluate the value of the differential Landé factor, 110.6Hz/G. by probing symmetrical σ-transitions.

Ultra-stable clock laser system development towards space applications.

The increasing performance of optical lattice clocks has made them attractive for scientific applications in space and thus has pushed the development of their components including the interrogation lasers of the clock transitions towards being suitable for space, which amongst others requires making them more power efficient, radiation hardened, smaller, lighter as well as more mechanically stable. Here we present the development towards a space-compatible interrogation laser system for a strontium lattice clock constructed within the Space Optical Clock (SOC2) project where we have concentrated on mechanical rigidity and size. The laser reaches a fractional frequency instability of 7.9 × 10−16 at 300 ms averaging time. The laser system uses a single extended cavity diode laser that gives enough power for interrogating the atoms, frequency comparison by a frequency comb and diagnostics. It includes fibre link stabilisation to the atomic package and to the comb. The optics module containing the laser has dimensions 60 × 45 × 8 cm3; and the ultra-stable reference cavity used for frequency stabilisation with its vacuum system takes 30 × 30 × 30 cm3. The acceleration sensitivities in three orthogonal directions of the cavity are 3.6 × 10−10/g, 5.8 × 10−10/g and 3.1 × 10−10/g, where g ≈ 9.8 m/s2 is the standard gravitational acceleration.

Comparison of two Strontium optical lattice clocks in agreement at the 10 −16 level

Two optical lattice clocks operated on the transition 1S0-3P0 of the 87Sr atom are now operational at the LNE-SYRTE laboratory, their comparison aims at demonstrating that no systematic effect has been overlooked in their respective accuracy budgets. In this proceeding we focus only on trapping effects, we discuss technical aspects of the calibration of the lattice induced light shifts, and we show the observation of the second order light shift. Data resulting from the comparisons are reported and discussed.

Frequency tripled 1.5 µm telecom laser diode stabilized to iodine hyperfine line in the 10−15 range

We report on telecom laser frequency stabilization to narrow iodine hyperfine line in the green range of the optical domain, after a frequency tripling process using two nonlinear PPLN crystals. We have generated up to 300 mW optical power in the green (P_3ω), from 800 mW of infrared power (P_ω). This result corresponds to an optical conversion efficiency η = P_3ω/P_ω ~ 36 %. To our knowledge, this is the best value ever demonstrated for a CW frequency tripling process. We have used a narrow linewidth iodine hyperfine line (component a₁ of the ¹²⁷I₂ R 35 (44-0) line) to stabilize the IR laser yielding to frequency stability of 4.8×10^-14τ^-1/2 with a minimum value of 6×10^-15 reached after 50 s of integration time. The whole optical setup is very compact and mostly optically fibered. This approach opens the way for efficient and elegant architecture development for space applications as one of several potential uses.

Contributing to TAI with Sr optical lattice clocks

In this paper, we present recent experiments conducted with two 87Sr optical lattice clocks operated at LNE-SYRTE. We report on the first calibrations of TAI with optical clocks, a necessary step towards the redefinition of the SI second. Additionally, we report on the experimental realization of a cavity-assisted non-destructive detection whose improved signal-to-noise ratio can improve the stability of optical clocks by reducing the Dick effect instability contribution, possibly beyond the quantum projection noise. Finally, we discuss the possibility to operate lattice clocks with semi-conductor sources as a lattice trap laser, by evaluating the frequency shift induced by their incoherent background light.