This thesis addresses the critical requirement for pressure monitoring in proximity to sensitive instrumentation within confined space environments. The study specifically targets the challenges posed by high-orbit conditions, including elevated radiation exposure, to accurately characterize and evaluate degassing phenomena. This measurement is particularly critical given the influence of out gassing on the pressurization of satellite cavities, the associated risks, and the design constraints and operational procedures (such as decontamination and startup procedure) of satellites. Currently, there are no solutions to address this measurement.

This subject was study during a R&T project (DTN/QE/LE.2023-0011105) involving the Contamination Department (D. Faye) and FEMTO-ST (J.-C. Beugnot). We also demonstrate an optical fiber Pirani gauge sensor. During this project, the design of the sensor was optimized for space applications. It has shown that a 25 mm long thinned optical fibre (i.e. a single glass thread) can be heated by a laser with a power of a few mW and working in the same way as a Pirani gauge. Several tests campaign was conduct at CNES Toulouse (2024-2025) to validate the sensor.

Fibre optic sensors exploit the properties of light guided in a fibre to measure various physical parameters, such as temperature, pressure, stress and strain. Their immunity to electromagnetic fields, long-term stability and compatibility with extreme environments make them a reliable solution for precision thermometry. They operate via changes in the intensity, phase, polarisation or frequency of the optical signal induced by the external environment. In our case of optical fiber Pirani gauge, a variation of pressure is link to a variation of temperature. During the R&T project, laboratory systems that were incompatible with those used in space were employed to demonstrate the sensor's proof of concept.

Today, we are proposing a thesis project for the design, creation, test and characterize of a temperature fiber interrogator compatible with space environment. 

The interferometric method, and specifically the multimode interferometric method obtained by thinning an optical fibre, is the simplest solution for measuring temperature variations in a space environment as it does not require complex optoelectronic components. However, interferometric methods measure the combined effects of stress and temperature. In our case, thinned optical fibres are highly sensitive to mechanical deformation. This was observed during the R&T project.

We propose to use a distributed temperature sensor (DTS) based on Raman scattering for depressurization measurement.

The principle of Raman scattering temperature measurement is based on Raman spectroscopy combined with optical reflectometry in the time domain. A light pulse is sent into the optical fiber. The light propagating forward generates backscattered Raman light at two distinct wavelengths. (+/-13.2 THz in silica) from all points of the fiber. The amplitude of the anti-Stokes light depends heavily on temperature and provides a relative measurement along the optical fiber. In fact, it is necessary to have a known temperature reference during the measurement. The temperature profile inside the optical fiber is calculated by taking the ratio of the amplitude of the Stokes light to the anti-Stokes light.

The Raman scattering method has the advantage of being sensitive only to temperature. There is currently no instrument or proof of concept for measurements of a few centimeters. In the state of the art, spatial resolution of Raman scattering instruments is limited to a few tens of centimeters because the Raman efficiency in silica is very weak (60 dB lower than incident light). To detect a very weak signal coming from a small part of fiber (i.e. 25mm for fiber Pirani gauge), we propose to use single photon avalanche detection systems (SPAD), which have a very weak detection level. AUREA technology (France) develops SPAD for space telecommunications.  Consequently, all components of DTS for space (this project) can be compatible with space environments.

Developing a Raman interrogator capable of measuring temperature over a 2 cm fiber section would be fully compatible with Pirani gauges in space environments. More generally, this system would enhance the spatial resolution of distributed fiber optic temperature sensors by a factor of 10, representing a significant advancement.

During this Phd, two test campaigns every year will be carried out at CNES in Toulouse. 

The FEMTO-ST (J-C. Beugnot)/CNES(D. Faye)/AUREA technology (J. Cussey) consortium. FEMTO-ST is an expert in fiber optic sensors. AUREA technology a Besancon provides single photon avalanche and is present in R&T program for space telecommunication.

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For more Information about the topics and the co-financial partner (found by the lab!); contact Directeur de thèse - jc.beugnot@femto-st.fr

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 13th, 2026 Midnight Paris time!