Radiation testing of thin optical coatings for space requires different approaches compared to bulk optical components or other material samples. In contrast to thicker samples, already particles of lower energy and thus lower range in the material will deposit high levels of dose in functional areas. In this paper we will discuss those differences and show ways to develop optimized test strategies.
Optical fibers are used routinely in harsh environments for signal transmission or sensing applications . Whereas the individual challenges originating from very high or very low temperatures, vacuum or ionizing radiation were extensively studied, the effects of combinations of these conditions were not investigated widely.
This paper discusses proton-induced radiation effects in vertically aligned carbon nanotubes (VA-CNT). VACNTs exhibit extremely low optical reflectivity which makes them interesting candidates for use in spacecraft stray light suppression. Investigating their behavior in space environment is a precondition for the implementation on a satellite.
Testing optical fibers for their response to ionizing radiation is unavoidable if their properties in radiation environments need to be known. So far, no model exists that would be able to predict the behavior of optical fibers in the presence of radiation, for example because too many, mostly unknown parameters influence the changes in the fiber.
To obtain reliable results from irradiation tests of optical fibers a well-defined setup and thorough experience is needed to avoid erroneous data that might lead to wrong decisions for the final application.
This presentation tries to introduce basic concepts of radiation testing of optical fibers, focusing on not so well known influences or typical errors. Focus will be laid on the measurement of radiation-induced attenuation (RIA) in optical fibers.
Ionizing radiations affect installed electronics, limit equipment lifetimes and eventually alter materials both in space applications as well as high energy accelerators and physics experiments. In order to monitor radiation levels and predict equipment and material lifetimes, an accurate radiation dosimetry is highly important and very challenging often due to two main reasons: (i) large areas and (ii) extended dose range of interest.
In this paper we present a validation of distributed Raman temperature sensing (RDTS) at the CERN high energy accelerator mixed field radiation test facility (CHARM), newly developed in order to qualify electronics for the challenging radiation environment of accelerators and connected high energy physics experiments. By investigating the effect of wavelength dependent radiation induced absorption (RIA) on the Raman Stokes and anti-Stokes light components in radiation tolerant Ge-doped multi-mode (MM) graded-index optical fibers, we demonstrate that Raman DTS used in loop configuration is robust to harsh environments in which the fiber is exposed to a mixed radiation field. The temperature profiles measured on commercial Ge-doped optical fibers is fully reliable and therefore, can be used to correct the RIA temperature dependence in distributed radiation sensing systems based on P-doped optical fibers.
HOBAN (Development of Hard Optical Fiber BrAgg GratiNgs Sensors) is an European H2020 project granted by Kic InnoEnergy and aiming the development of fiber-based temperature and strain monitoring systems that can withstand harsh nuclear environment (350°C temperature and MGy dose levels). The objective will be achieved by employing ‘ad hoc’ fiber Bragg grating (FBG) sensors and their associated instrumentation system which will bring to the market new tools for optimizing the running and the services in current and future nuclear power plants. We’ll present the challenges associated with this project and recent advances at the OFS conference.
The radiation sensitivity of Bragg gratings written with a femtosecond IR laser was measured for the first time.
Type I-IR and type II-IR gratings were written into hydrogen loaded as well as unloaded fibers of distinctly different
radiation sensitivity with the intention to find extremely radiation resistant gratings for temperature or stress
measurements in radiation environments, as well as very radiation sensitive ones for radiation dose measurements. With
a highly radiation-hard F-doped fiber we found a radiation-induced wavelength shift between about 3 and 7 pm after a
dose of 100 kGy. These are the lowest shifts observed so far. In such fibers it is very difficult to write gratings with an
UV laser. However, gratings made of the highly radiation-sensitive fibers only showed shifts of about the same size as
those made of the quite radiation-insensitive Corning SMF-28e fiber. This was already observed with UV laser gratings
written in such fibers.
Three different fibre optic radiation sensor systems are described. Two are based on the radiation-induced attenuation increase of radiation sensitive doped fibres, whereas with the third system the Cerenkov light generated by relativistic electrons in radiation hard undoped fibres is detected. All three systems are successfully used for beam optimization and dose measurement at three German electron accelerators.