PhD position, Experimental optics and Simulation for Scattered Light Metrology (M/F)

Job Description

Thesis Subject

The PhD project aims to develop and implement an instrument for identifying optical components in the Virgo gravitational wave detector benches that are responsible for stray light. This instrument, called the "Straylight Source Identifier" (SLS-Id), uses the principle of "Optical Frequency Domain Reflectometry", which is implemented in high-precision, non-contact distance measurements. The object whose distance and scattered light contribution are to be evaluated is illuminated by a continuously wavelength-swept laser. The backscattered light from the object is collected and combined with a part of the incident laser considered as a local oscillator. The interference between the reflected light and the local oscillator produces a sinusoidal temporal signal whose frequency is proportional to the distance to the object and the laser frequency sweep rate. By knowing the sweep rate, the position of the scattered light source—and thus the identification of the component—can be determined. The amplitude of the fringes provides information on the fraction of light backscattered by the object, offering an indication of the intrinsic scattering level of the component considered as a stray light source. This approach has been adopted for the LISA project (space-based gravitational wave detector) but remains unprecedented in the context of terrestrial gravitational wave detectors such as Virgo, LIGO, and KAGRA. Its remarkable feature is that it allows the optical scattering of components to be characterized through system-level measurements, enabling the identification of "pathological" components once integrated into optical benches. This contrasts with the current methodology, where component characterization requires disassembly for integration into a dedicated instrument (such as a "Scatterometer").

The advantages of this new approach are evident and will be of interest to the entire community of terrestrial gravitational wave detectors.

The PhD project is structured around three main axes:

1- Optimization of the frequency-swept laser performance and the recombination system for backscattered light and the local oscillator. Analysis and optimization of the SLS-Id's sensitivity. This experimental work involves skills in photonics, fiber optics, control systems, weak signal detection methods, and signal processing to develop the best detection strategy. Depending on the candidate's expertise, an approach using artificial intelligence or machine learning to exploit interferometric signals from the SLS-Id may be considered.

2- Analysis of the SLS-Id's sensitivity in optical configurations representative of Virgo benches. Extraction of scattering parameters specific to each component and comparison with the component's scattering indicatrix (the Bidirectional Reflectance Distribution Function, measured or provided by the manufacturer). This involves correlating measurements and simulation results. An analytical study of the electromagnetic field of backscattered light will be developed to understand the speckle phenomena inherent in coherent light interferometry. This study will be conducted in parallel with simulations using the optical design software "Zemax OpticStudio".

3- Implementation of the SLS-Id with Virgo benches. Definition, design, and integration of the optomechanical interface between the SLS-Id and the bench to be tested, along with the interferometric measurements. Analysis of the measurements in view of the characterization of optical bench components. This experimental activity will be partially conducted at the sites where the benches are assembled (Annecy, France, and the vicinity of Pisa, Italy).

Your Work Environment

This PhD is funded as part of an interdisciplinary research project between the joint research units ARTEMIS (UMR7250, Nice, France) and the Laboratoire d'Annecy de Physique des Particules (LAPP, UMR5814, Annecy, France), both under the CNRS. The PhD candidate will be co-supervised by these two teams.
The candidate will primarily work within the ARTEMIS joint research unit, based at the Observatoire de la Côte d'Azur in Nice. There, he or she will contribute to the instrumental development of the project and the analysis of interferometric signals. The application to the Virgo benches (defining strategies and/or implementing the SLS-Id) will be conducted in collaboration with LAPP. As part of this, short-term missions for meetings or integration and testing phases should be expected, both at LAPP (Annecy, France) and at the Virgo site (near Pisa, Italy).
Presentation of the teams the candidate will work with:
- ARTEMIS is the successor to the team founded in 1987 by Alain Brillet (2017 CNRS Gold Medal laureate), who initiated the Virgo gravitational wave detector project. Since then, ARTEMIS's activities have expanded to include the LISA and Einstein Telescope projects, covering experimental aspects, data analysis, and cosmology related to gravitational waves. Specifically, the unit brings together experts in laser metrology and scattered light, who have played a key role in managing the pre-stabilized laser system of Virgo and the scattered light metrology in the LISA benches.
- LAPP has extensive experience in the operation and integration of the Virgo detector. LAPP has been responsible for coordinating the commissioning of the entire detector since 2022, and since 2016, it has a major role in the study of the detector's dominant noise sources. It will provide expertise on the knowledge of Virgo benches (design, criticality of benches/components, integration schedule) and scenarios for the recombination of scattered light in the Virgo detector to design integration configurations for the SLS-Id instrument with the selected benches.
- Additionally, exchanges with the teams from the LIGO (USA) and KAGRA (Japan) projects, Virgo's counterparts, will offer opportunities for visits and/or international collaborations with these laboratories.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

The research professions