François-Xavier Esnault

PHARAO laser source flight model: Design and performances

In this paper, we describe the design and the main performances of the PHARAO laser source flight model. PHARAO is a laser cooled cesium clock specially designed for operation in space and the laser source is one of the main sub-systems. The flight model presented in this work is the first remote-controlled laser system designed for spaceborne cold atom manipulation. The main challenges arise from mechanical compatibility with space constraints, which impose a high level of compactness, a low electric power consumption, a wide range of operating temperature, and a vacuum environment. We describe the main functions of the laser source and give an overview of the main technologies developed for this instrument. We present some results of the qualification process. The characteristics of the laser source flight model, and their impact on the clock performances, have been verified in operational conditions.

Stability of the compact cold atom clock HORACE

HORACE is a compact cold cesium atom clock which is being developed in LNE-SYRTE for space applications and onboard systems. The operation of this clock is different from fountains since the laser cooling, the microwave interrogation and the detection are sequentially performed inside the spherical microwave cavity. We recently achieved short term stability of 5.5 10-13 tau-0.5 reaching the 10-14 level at 3000 sec. We report in this paper recent developments and improvements, particularly on the cooling sequence. We also study the main limitations.

Reaching a few 10 −13 τ −1/2 stability level with the compact cold atom clock HORACE

HORACE is a compact cold cesium atom clock which is being developed in LNE-SYRTE for space applications and onboard systems. The operation of this clock is different from fountains since the laser cooling, the microwave interrogation and the detection are sequentially performed inside the spherical microwave cavity. The entire simplified operation sequence is described. A short term relative frequency stability of 2.2 10-13 tau-1/2 is achieved. Preliminary results on mid term show that a level of 4 10-15 is reached after 5 103s of integration. Limitations are investigated.

A new design of ECLD for compact atomic clocks

Cold atom clocks would take great benefits of microgravity environment. In Relation with the clock developments, we work on miniature laser-cooling optical benches. In this article we describe a new design of compact external cavity laser diode, which exhibits up to 80 mW at the output of the ECLD for a diode current of 100 mA and a line width of about 150 kHz.

Frequency synthesis from Cryogenic Sapphire Oscillator

In this paper we present several configurations enabling to obtain a low-noise 5 MHz signal from the 100 MHz delivered by the frequency synthesis of a Cryogenic Sapphire Oscillator. The residual single-sideband phase noise of several dividers is reported. Especially the noise of a custom built regenerative divider has been measured to be around ℒ5MHz(1 Hz) = -145 dBc/Hz. This performance is sufficient to measure the residual phase noise of an ultra-stable quartz crystal resonator using a carrier suppression system.

Phase noise measurements of AlN contour-mode resonators

In this paper, the phase noise of aluminum nitride (AlN) contour-mode resonators is investigated using a passive measurement system with carrier suppression. The purpose is to make careful measurements of the performance of AlN resonators in order to better understand and clarify previously reported frequency instability in these devices. The resonant frequencies of the resonators are around 220 MHz. The motional parameters, the thermal behavior, and the nonlinear power effect of these resonators have been evaluated. Then, the principle of the noise measurement system is reviewed, and the resonator conditioning is shown. Finally, the noise measurements of the resonators are presented and discussed.

A compact optical bench for laser cooling

We present the architecture of a A4 size optical bench developed for the compact cold atom clock HORACE. This proceeding focuses on two original sub systems as compact extended cavity laser diode with optical isolator places inside the laser cavity, and very compact saturated absorption systems.