Centre National d'Etudes Spatiales
Job title:
005 Ultra-stable two-photon microcell optical frequency reference
Company:
Centre National d’Etudes Spatiales
Job description
With the contribution of atomic spectroscopy, MEMS technologies and integrated photonics, miniaturized atomic clocks, sensors and instruments have been developed for around 20 years. This field of research, initiated in 2004 with the demonstration at NIST of the first microwave chip-scale atomic clock (CSAC), has since experienced growing popularity, due to its strategic interest and the plethora of applications (GNSS, secure communications, PNT systems, etc.) it covers. Current commercial CSACs lose about 1 microsecond per day, a hundred times less than quartz oscillators, within a comparable volume-consumption budget. However, the frequency noise of their laser (VCSEL) limits their short-term frequency stability while the presence of a buffer gas pressure in their cell induces a collisional shift that compromise their long-term stability.Recent years have seen a relevant interest towards the development of new-generation miniaturized optical atomic clocks. In this domain, sub-Doppler spectroscopy techniques, based on the interaction of hot alkali atoms contained in a vapor cell with two counter-propagating laser fields obtained from a single laser, constitute an extremely attractive approach due to their simplicity and integration potential.Among various methods, the 2-photon absorption spectroscopy of the Rb atom at 778 nm offers very promising features. Using a Rb microcell and an external-cavity diode laser, NIST has demonstrated a compact optical reference with a fractional frequency stability of 1.8×10-13 at 1 s and approaching 10-14 at 100 s. This work led in the USA to the start in 2021 of the CROC (Compact Rubidium Optical Clock) project, targeting the development of deployable industrial-grade Rb cell clocks. Work has also been undertaken with this approach in Europe, in particular at FEMTO-ST, within the framework of CNES and EU-funded projects. Competitive stability results of 3×10-13 at 1 s and 3×10-14 at 100 s have been recently reported at FEMTO-ST.In this context, and based on the experience acquired at FEMTO-ST, the PhD thesis targets the upgraded development, progress and metrological characterization of an ultra-stable microcell optical reference based on two-photon transition of Rb atom at 778 nm. A fractional frequency stability in the 10-14 range at 1 s and 1 hour integration time is targeted in a very simple laser system architecture. Such an optical reference might contribute to the positioning or navigation of GNSS-denied vehicles, nano-satellites, and could find interest in the implementation of ambitious space missions that require precise timekeeping.Clock stability limitations to overcome are well-identified and suggest main research axis to be investigated by the candidate during his/her PhD work. The frequency stability of the Rb microcell reference is today limited by three major contributions: 1/ the laser frequency noise, which degrades the short-term stability of the atomic reference through an intermodulation effect, 2/ the poor signal-to-noise ratio of the atomic resonance explained by the reduced atom-field interaction length, the insufficient blue photon collection efficiency, and the limited number of Rb atoms involved in the atom-field interaction, and 3/ the presence of contaminants or residual gases in the microfabricated cell, which causes line broadening (~10-20 MHz/Torr) of the optical atomic resonance.Accordingly, the objectives of the PhD work will involve: 1/Implementation of a new ultra-low frequency noise laser to reduce the intermodulation contribution and improve the reference short-term stability, 2/ Development of original micro-fabricated cell architectures offering improved internal atmosphere purity, to access the detection of narrower optical resonances, as well as increased atomic signal and shot noise reduced photon (optimized fluorescence collection). The new advanced cell will be implemented in a dedicated thermally and magnetically optimized small-size physics package. 3/ Implementation of innovative light shift mitigation techniques to improve the reference mid- and long-term frequency stability, 4/ Short-term and long-term stability metrological characterization of the Rb microcell two-photon optical reference. A 778 nm signal generated from an optical frequency comb locked to an ultra-stable cavity will be used as a reference, for beat-note measurements.The PhD candidate will work at the interface between the OHMS and MOSAIC groups at FEMTO-ST. The candidate will interact with researchers, engineers, technicians and will benefit from the support and skills of FEMTO-ST internal services (electronics/mechanics/computing), in an environment with access to a large number of instruments dedicated to time-frequency metrology and clean-room facilities. The candidate will present his/her work in international conferences and will target high-impact publications.For more Information about the topics and the co-financial partner (found by the lab !);contact Directeur de thèse –Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online before March 14th, 2025 Midnight Paris time !ProfilMaster 2 with knowledge and competences in disciplines such as applied physics, optics, electronics, instrumentation, experiment interfacing (Python programming preferred). The PhD work will involve interdisciplinary studies with lasers/MEMS technologies/electronics/metrology, contributing to high-precision measurements. Some background with atomic/quantum physics, but also clean-room techniques and processes (lab works for example), would be clear plus-values.
Expected salary
Location
Besançon, Doubs
Job date
Wed, 05 Feb 2025 07:22:20 GMT
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