Assessment of Ge-doped optical fibres as a TSL-mode detector

International audienceThis study analyses the thermally stimulated luminescence or thermoluminescence (TL) glow curve between 300 and 773 K of germanium-doped silica optical fibre. A main glow peak at 530 K with a characteristic spectral emission centred at 400 nm is found. Both features are particularly suitable for dosimetry. Thus, an investigation by the TL technique of some first clinically relevant features of a TL sensor like the dose- and dose rate-responses is examined. The presented studies show that germanium doped silica fibres have potential dosimetric properties and should be excellent TL-mode detectors in instances of radiotherapy (clinical dosimetry) and in-vivo radiation dosimetry as well in the field of nuclear facilities

Dimensionless study of the total response of thermally stimulated luminescence

The response of thermally stimulated luminescence (TSL) is investigated theoretically. An original dimensionless treatment is proposed, first to highlight the key dimensionless factors rationalizing the competition between the mechanisms at play during the TSL readout, and second to clean up the approach from any particular values of the relevant physical parameters. The approach holds for an unlimited number of interactive traps. The total response from a current trap is derived and cast into simple formal expressions as a function of the recombination cross-section, the set of trapping cross-sections and of initial trap occupancies (i.e. those existing before the readout of the current peak). This allows one to calculate each peak response by taking proper account of carrier transfers accompanying the successive peak readouts

A physical model of the photo- and radiation-induced degradation of ytterbium-doped silica optical fibres

International audienceWe propose a model to describe the photo-or/and the radiation-induced darkening of ytterbium-doped silica optical fibers. This model accounts for the well-established experimental features of photo-darkening. Degradation behaviors predicted for fibers pumped in harsh environments are also fully confirmed by experimental data reported in the work by Duchez et al. (this proceeding), which gives a detailed characterization of the interplay between the effects of the pump and those of a superimposed ionizing irradiation (actual operation conditions in space-based applications for instance). In particular, dependences of the darkening build-up on the pump power, the total ionizing dose and the dose rate are all correctly reproduced. The presented model is a 'sufficient' one, including the minimal physical ingredients required to reproduce experimental features. Refinements could be proposed to improve, e.g., quantitative kinetics

The interplay between photo-and radiation-induced darkening in ytterbium-doped fibres

International audienceThis letter demonstrates a remarkable interplay between photo-and radiation-induced darkening of ytterbium-doped alumino-silica optical fibres operated in amplifying conditions and harsh environments (as e.g. in space-based applications). Influences of the pump power, ionizing dose and dose rate on this interaction are characterized. The pump is capable of accelerating or slowing-down the radiation-induced darkening build-up depending on the ionizing dose. The steady state photo-radio-darkening level is independent of the dose and at least equal to the equilibrium level of pure photo-darkening. This lower limit is notably reached at low dose rates, including those encountered in space. We therefore argue that photo-resistant ytterbium-doped fibres will resist against a space mission, whatever the dose

All-fiber sensors for radiation measurements in radiotherapy

The paper presents the development and investigation of distributed and a quasi-distributed fiber optic sensors for the real-time monitoring of radiations during cancer treatments. Both sensors rely on ad-hoc developed nanoparticle-doped optical fibers with enhanced sensitivity to radiation. The distributed sensor is interrogated with an OFDR-based instrument and allows the reconstruction of the spatial dose distribution along the fiber. The quasi-distributed sensor is implemented through fiber Bragg gratings inscribed with a femtosecond laser in the few-mode section of a single mode-multi mode-single mode interferometer

Ionizing radiation profiling through the induced refractive index change in backscattering-enhanced optical fibers

Enhanced Rayleigh backscattering optical fibers, interrogated by an optical frequency domain reflectometer, are used to perform remote real-time measurements of X-ray irradiation profiles, with possible application as dosimeters in radiotherapy treatments. The enhanced Rayleigh backscattering is obtained by proper engineering of the composition of fiber core, either by introduction of Aluminum or Magnesium silicate nanoparticles as radiation-sensitive dopants. A detectable radiation-induced refractive index change can be spatially resolved through the measurement of the frequency shift of the Rayleigh backscattering along the fiber. It is experimentally demonstrated that two mechanisms of radiation-induced refractive index change take place. At doses nearly compatible with those delivered in radiotherapy, a negative refractive index is induced, whereas at high doses the change is positive. This behavior is also confirmed by the shift of Bragg wavelength of a fiber Bragg grating inscribed in the nanoparticles-doped fiber and used as a reference

RÉDUCTION DU PHOTO-NOIRCISSEMENT PAR UN CO-DOPAGE AU LANTHANE OU AU CÉRIUM DES FIBRES OPTIQUES DOPÉES AU THULIUM POMPÉES À 1070 NM

National audienceRÉSUMÉ Les fibres optiques dopées au thulium pompées à 1,07 µm offrent la perspective de lasers et amplificateurs fonctionnant à de nouvelles longueurs d'onde. Ce système permet d'envisager de nombreuses transitions optiques encore inexploitées dans des fibres à base de silice. Le principal verrou technologique de ce système est le photo-noircissement. Nous présentons ici la réduction du photo-noircissement en co-dopant la silice avec du cérium ou du lanthane. Un modèle pour le photo-noircissement est proposé. Ce modèle implique un processus séquentiel faisant intervenir un défaut et un changement de valence de Tm 3+ en Tm 2+. Les effets bénéfiques du co-dopant sont aussi expliqués grâce à ce modèle

Distributed X-ray dosimetry with optical fibers by Optical Frequency Domain Interferometry

This article reports on the first demonstration of in situ, real-time dosimetry realized with an enhanced backscatttering optical fiber, and a high resolution optical backscattering reflectometry measurement. This work is devised to overcome the current problems in monitoring radiotherapy treatments, in particular, the difficult evaluation of not only the actual X-ray dose that is accumulated on the target volume but also the distribution profile of the ionizing radiation beam. Overall, the research aims at developing a dose sensor with the most demanding features of small form factor, spatial profiling, and remote interrogation. The experiments have been conducted by evaluating the spatial profile of radiation-induced spectral shift of the Rayleigh backscattering along an optical fiber exposed to X-rays. The sensing element is a section of specialty optical fiber whose Rayleigh backscattering signature changes under ionizing radiation. The specialty fiber is designed to exhibit an enhanced backscattering, in order to overcome the poor sensitivity to radiation of standard optical fibers that are normally, used in telecommunications. The enhanced sensitivity is achieved by doping the core with either aluminum or magnesium nanoparticles, and two different fibers have been fabricated and tested. The experimental results show the capability of real time detection of the radiation profile from high-dose rates (700 Gy/min) to low-dose rates (2 Gy/min). Moreover, different sensing mechanisms and responses to high- and low-dose rates are evidenced. A comparison with a quasi-distributed sensing system based on an array of fiber Bragg gratings (FBGs) is discussed, highlighting the superior performance of the backscattering approach in terms of sensitivity and spatial resolution, whereas the array of FBGs exhibits an advantage in terms of sampling speed

Preliminary investigation of radiation dose sensors based on aluminum-doped silicate optical fibers

The paper reports on the first demonstration of in-situ, real-time dosimetry realized with an enhanced back-scattering optical fiber and a high-resolution optical back-scattering reflectometry measurement. This work is devised to overcome the current problems in monitoring radiotherapy treatments, in particular the difficult evaluation of not only the actual x-ray dose that is accumulated on the target volume, but also the distribution profile of the ionizing radiation beam. The experiments have been conducted by evaluating the radiation-induced spectral shift of the Rayleigh back-scattering along the fiber under test during x-ray exposure, in a radiation chamber. The sensing region is a section of aluminum-doped silicate fiber, that overcomes the poor sensitivity to radiation of standard, germanium-doped, silicate fibers for telecom applications. The preliminary results show that it is possible to remotely track the x-ray dose at high dose rates (700 Gy/min) and at rates closer to therapeutic values (22 Gy/min). A linear relationship between accumulated dose and spectral shift has been found. This research aims at developing a dose sensor with the most demanding features of small form factor, spatial profiling and remote interrogation