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Portail > Offres > Offre UMR6174-SARDJA-008 - H/F Chercheur Post-Doctorant

M/FDevelopment of an ultra-stable cryogenic silicon cavity below 1 K

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Français - Anglais

Date Limite Candidature : mardi 19 octobre 2021

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General information

Reference : UMR6174-SARDJA-008
Workplace : BESANCON
Date of publication : Tuesday, September 7, 2021
Type of Contract : FTC Scientist
Contract Period : 18 months
Expected date of employment : 15 October 2021
Proportion of work : Full time
Remuneration : From 2100€ To 3000€ to be defined
Desired level of education : PhD
Experience required : 1 to 4 years


The aim of this work is to study a new generation of ultra-stable optical Fabry-Perot cavity. Such a cavity, made from single crystal silicon maintained below 1 K, will be used as the frequency reference for an ultra-stable laser. It will pave the way for the next generation of ultra-stable lasers with fractional frequency stability lower than 10-17.
As a first step, the Fabry-Perot cavity will be placed and cooled down in a dilution cryostat. A laser source will be frequency-locked to the cavity in order to access its optical properties. Refine measurement of those properties is the second step. The last step will focus on performances characterization to demonstrate the potential of this ultra-low temperature reference.


The post-doctoral researcher will carry out the experimental work according to the mission within a Time-Frequency metrology laboratory. The main identified activities are:
- Scientific and technical duties: installation of the cavity mount, the optical setup, and the locking electronics; laser frequency stabilization; characterization.
- Project management.
- Supervision of doctoral students, technicians …
- Communication of the project results (writing of peer-reviewed articles and presentations at international conferences).

Within the scientific and technical activities, we identify the following tasks:
- Detection of the error signal (Pound-Drever-Hall).
- Measurement and optimization of the cavity vibration sensitivity in the cryostat.
- Management and measurement of the thermal perturbations acting on the cavity.
- Study of the motion of the cavity housed in the cryostat (inducing Doppler effect) and implementation of compensation techniques.
- Laser power stabilization.
- Characterization of the cavity parameters, such as finesse or optical power sensitivity, at various cryogenic temperatures; measurement of the minimum achievable operating temperature.
- Implementation of a dedicated measurement setup to characterize the laser locked to the cavity.


The required skills are those of an experimental scientist in optical frequency metrology: lasers frequency lock, lasers characterization (intensity and phase noise measurements). Given the project objectives, an experience with ultra-stable cavities and / or cryogenic systems will be an asset.
The list of expected experimental skills for an experimental scientist in optical frequency metrology are the following:
- free space and guided Gaussian optics (coupling the laser to the cavity, noise-compensated fiber links).
- Basic knowledge of control theory (mandatory to implement and tune the various locks).
- Low frequency analog electronic for understanding, debugging and optionally designing some electronic functionalities (photodetector circuits, loop filters …).
- Temperature control.

The following additional skills will be welcome:
- Instrumentation and low noise electronics.
- Programming in Python, C/C++ for data processing, device interfacing.
- Use of Linux operating system (Debian).
- Digital electronic and FPGA .
- Ultra-high vacuum.

Work Context

The candidate will integrate the OHMS team (about 25 people, http://teams.femto-st.fr/equipe-ohms/) in the time and frequency department of FEMTO-ST (www.femto-st.fr). An important activity is the development of optical references such as cavity-stabilized lasers, a single-ion optical clock (Yb+), a Supperradiant ultra-stable laser and cesium-cell stabilized lasers. The candidate will benefit from the support of the electronic, IT and mechanical workshops of FEMTO-ST. A measurement platform dedicated to the short-term frequency stability and ultra-low phase noise will be also available (http://oscillator-imp.com/dokuwiki/doku.php).
The project (including this post-doctoral position) is founded by the European Union (JRP NEXTLASERS from the EMPIR program of EURAMET). The future ultra-stable lasers that will be used in the next generation of atomic clocks are studied in the frame of this project by partners of the consortium (PTB, SYRTE, INRIM, RISE...). The OHMS team focuses the realization of a frequency-stabilized laser based on a single crystal silicon Fabry-Perot cavity operated bellow 1 K. The material and the cryogenic temperature induce a strong reduction of the cavity thermal noise compared with room temperature and ULE-made cavity (factor higher than 2500). Thus, the improvement may allow fractional frequency stability better than 10-17.

Constraints and risks

Laser radiation exposure

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