We report the main characteristics and performances of the first – to our knowledge – prototype of an ultra-stable cavity designed and produced by industry with the aim of space missions. The cavity is a 100 mm long cylinder rigidly held at its midplane by an engineered mechanical interface providing an efficient decoupling from thermal and vibration perturbations. The spacer is made from Ultra-Low Expansion (ULE) glass and mirrors substrate from fused silica to reduce the thermal noise limit to 4x10-16. Finite element modeling was performed in order to minimize thermal and vibration sensitivities while getting a high fundamental resonance frequency. The system was designed to be transportable, acceleration tolerant (up to several g) and temperature range compliant [-33°C; +73°C]. The axial vibration sensitivity was evaluated at 4x10-11 /(ms-2), while the transverse one is < 1x10-11 /(ms-2). The fractional frequency instability is < 1x10-15 from 0.1 to few seconds and reaches 5-6x10-16 at 1s.
The ESA mission “Space Optical Clock” project aims at operating an optical lattice clock on the ISS in approximately 2023. The scientific goals of the mission are to perform tests of fundamental physics, to enable space-assisted relativistic geodesy and to intercompare optical clocks on the ground using microwave and optical links. The performance goal of the space clock is less than 1 × 10-17 uncertainty and 1 × 10-15 τ-1/2 instability. Within an EU-FP7-funded project, a strontium optical lattice clock demonstrator has been developed. Goal performances are instability below 1 × 10-15 τ-1/2 and fractional inaccuracy 5 × 10-17. For the design of the clock, techniques and approaches suitable for later space application are used, such as modular design, diode lasers, low power consumption subunits, and compact dimensions. The Sr clock apparatus is fully operational, and the clock transition in 88Sr was observed with linewidth as small as 9 Hz.
Comparisons between three Cs fountains are described. All three LNE-SYRTE
fountain clocks are now using a cryogenic sapphire oscillator as
a starting point to generate the microwave probe signal. As a result, all
three fountains have a fractional frequency instability in the 10-14 range
at 1 s. All three fountains are also using a recently developed generation
of microwave synthesizers allowing to switch the microwave probe signal
without introducing detrimental phase transient. Several series of measurements
have been made totalizing more than 80 days of simultaneous
operation under optimized conditions of a pair of either fountains. Results
of these measurements are presented. Finally, modifications of the
FO2 fountain has been completed to allow simultaneous operation with
Rb and Cs. Operation with Rb leads to a fractional frequency instability
of 6.3 × 10-14τ-1/2.
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.
The new atomic Rb-Cs fountain should confirm the recent theoretical calculations relating to the collisions of rubidium atoms. According to this theory, the displacement of the frequency of clock due to the collisional shift was predicted to be 15 times lower for 87Rb than for 133Cs at equal density. Using Rb instead of Cs in a foundation standard may lead to an order of magnitude improvement in frequency stability together with an excellent accuracy. In this paper we describe the operation of a laser cooled 87 frequency standard and present a new measurement of the 87Rb ground state hyperfine frequency with a relative accuracy of 2.4 10-15 by comparison with a Cs fountain atomic standard. In order to measure this, first we determined the absolute frequency of the reference H-maser by comparison with the LPTFs Cs fountain. Second, we corrected the measured frequency to take into account different systematic shifts: magnetic field, black body, microwave leakage, collisions. The measured frequency is 6 834 682 610.904 333 Hz. This value differs form previously published values1,2 by about 2-3 Hz and is 104 times more accurate.