Fiber-optic Radiation Research Articles

放射率の補正が不要な浸漬型光ファイバー温度計による溶接金属の温度計測

放射率の補正が不要な浸漬型光ファイバー温度計による溶接金属の温度計測

Online Temperature Detecting System in Hot Machining Process

A kind of optical fiber radiation pyrometer based on the theory of color comparison temperature measurement is designed in order to get the precise temperature on the appearance of work pieces during the process of plasma hot machining. In this article, the advantage of temperature measurement by optical fiber, the building of mathematic module for colorimetric temperature measurement, the application of key technology during the process of system building and the methods of reducing the interference is described in detail. The data calibrated and tested in blackbody furnace is given out. The results show that the precision of temperature measurement could reach to 0.5%. It is repetitiveness is well enough.

Experimental Study of Simultaneous Transmission of Ultrasonic Waves and Optical Radiation via Optical Fiber Couplers

This article presents the results of experimental studies of simultaneous transmission of ultrasonic waves and laser signals in optical fibers by the use of both the optical single mode and multimode fiber couplers. This work was aimed, among other things, at the study of the way the acoustic energy affects a laser beam. The light wave was guided into one of the coupler's arms. The optical power applied to one input of the coupler is separated into two coupler outputs according to the rate determined by the coupling coefficient. Only an ultrasonic wave generated by a sandwich type transducer is applied to the other arm of the coupler. In this experiment, as in case of the light wave, the acoustic power is separated into both the outputs. One can observe the interaction of both the waves on the two outputs - a modulation of the light wave by means of the ultrasonic wave is possible. The output signal was detected using a PIN diode and an optical power meter (OPM). Temporary courses were observed on an oscilloscope screen. The simultaneous transmission of ultrasounds and optical radiation in optical fibers can be used in the construction of medical equipment.

Poster - Wed Eve-53: Characteristics of Radiation Induced Light in Optical Fibers

Most electronic portal imaging devices (EPIDs) developed so far use a Cu plate/phosphor screen to absorb x rays. This approach uses a thin screen (∼ 2 mm) to obtain a high spatial resolution, however this results in a low quantum efficiency (QE) for megavoltage (MV) x rays (typically 2–4%). The phosphor screen also contains high atomic number (high‐Z) materials, resulting in an over‐response of the detector to low energy x rays in dosimetric verification. Our overall goal is to develop a new high QE MV x‐ray detector made of a low‐Z material for both geometric and dosimetric verification in radiotherapy. The approach is based on converting x‐ray energy into Cherenkov radiation in optical fibers. The design uses a thick (∼ 10–30 cm) matrix of optical fibres (to dramatically improve the QE) aligned with the incident x rays. This work investigates the characteristics of radiation‐induced light in optical fibers and demonstrates that the predominant light source in optical fibers under high energy irradiation is indeed Cherenkov radiation. Thus, the feasibility of using Cherenkov radiation as the primary light source in the proposed Cherenkov detector is validated. This work was supported by the National Sciences and Engineering Research Council of Canada (NSERC).

Paramagnetic germanium-related centers induced by energetic radiation in optical fibers and preforms

We investigated the creation processes of Ge-related paramagnetic point defects in silica fibers and preforms, doped with different amounts of germanium, and X-ray irradiated at several radiation doses. Different paramagnetic defect species, like GeE′, Ge(1) and Ge(2), were revealed by electron paramagnetic resonance measurements and their concentration was studied as a function of the irradiation dose. The comparison with the optical absorption spectra points out the main role of Ge(1) on the optical transmission loss of fibers in the UV region.

Mathematical modeling of random coupling between polarization modes in single-mode optical fibers: XVI. Depolarization and repolarization of polychromatic radiation in single-mode optical fibers with random inhomogeneities

The dependences of the degree of polarization of polychromatic radiation on the length of a single-mode optical fiber (SMF) with random inhomogeneities have been obtained by mathematical modeling. The case is considered where radiation having both polarization modes excited with equal weights of linear polarization is first introduced into a depolarizer of polychromatic radiation (a SMF segment with high linear birefringence) and arrives at an SMF with low linear birefringence. It is shown that the degree of polarization of radiation after transmission through the first segment becomes significantly suppressed and remains almost constant upon propagation through the second segment, after which it begins to sharply increase at some length; i.e., repolarization of radiation occurs. It is shown that repolarization of radiation depends weakly on the angle made by the axes of unperturbed linear birefringence of the first and second segments. The conditions for the length of the first segment (depolarizer) under which the degree of polarization remains minimum throughout the second segment are determined.

Radiation response behaviour of Al codoped germano-silicate SM fiber at high radiation dose

Radiation response behaviour of Ge+Al doped SM fiber fabricated by the solution doping process has been studied at room temperature with respect to 1310nm transmission wavelength under three different dose rates of 200, 400 and 600Rad/min to compare with that of standard Er doped as well as Ge doped SM fibers. Their radiation sensitivity has been observed with variation of dose rates, transmission wavelength along with their recovery nature. Radiation response behaviour of Al doped SM fiber is found to be slightly non-linear in nature with very low dose rate dependency. No saturation level was found upto 13Krad cumulative dose. Thermobleaching as well as photobleaching phenomena have also been studied. Gamma irradiated Al doped preform shows an absorption peak at around 300nm due to generation of Al (E′) defect center and gets annihilated after thermobleaching process. Gamma irradiated Al doped SM fiber shows prominent photobleaching effect on their optical attenuation with respect to the 850nm transmission wavelength. From ESR study resonance signals for Al3+ related radiation-induced defect centers are not clearly observed in this study. A very weak hyperfine pattern has been observed for gamma irradiated Al doped preform sample. The high radiation sensitivity along with linear response behaviour, low recovery and almost dose rate independence behaviour of the material system of Ge+Al codoped SM core optical fiber under gamma radiation shows their potential for application as fiber optic radiation sensor in comparison to the universal standard erbium doped SM fiber.

Depolarization of broadband radiation in optical fibers with the twisted structure of birefringence

The depolarization of broadband linearly polarized radiation that propagates in optical fibers with the twisted structure of birefringence is investigated. The basic relationships for calculating the degree of radiation polarization at the fiber output at arbitrary fiber lengths and arbitrary azimuths of the input linear polarization are obtained. The depolarization length (on the order of several meters) at which the degree of polarization decreases from unity to a certain residual level is found. It is shown that the depolarization length depends on the width of the spectrum of a radiation source, the magnitude of the fiber’s built-in linear birefringence, and the twist pitch. For long fibers (of a length exceeding 50 m), the residual degree of polarization depends on the azimuth of the input linear polarization.

Classical radiation in optical fibers as model for quantum entanglement

Using known description of the classical electromagnetic radiation propagating in optical fibers by the Schrodinger-like equation (Fock–Leontovich paraxial approximation), the model of entanglement phenomenon is considered. Gaussian light beams in optical fibers demonstrate a formal mathematical identity to Gaussian two-mode quantum fields. In view of this, the criterion of separability and entanglement of Gaussian light beams is implemented in fiber optics.

A study on the real-time radiation dosimetry measurement system based on optically stimulated luminescence**Supported by National Natural Science Foundation of China (10475112), Western Light Foundation of Chinese Academy of Sciences of 2005 Years

The optically stimulated luminescent (OSL) radiation dosimeter technically surveys a wide dynamic measurement range and a high sensitivity. Optical fiber dosimeters provide capability for remote monitoring of the radiation in the locations which are difficult-to-access and hazardous. In addition, optical fiber dosimeters are immune to electrical and radio-frequency interference. In this paper, a novel remote optical fiber radiation dosimeter is described. The optical fiber dosimeter takes advantage of the charge trapping materials CaS:Ce, Sm that exhibit OSL. The measuring range of the dosimeter is from 0.1 to 100 Gy. The equipment is relatively simple and small in size, and has low power consumption. This device is suitable for measuring the space radiation dose and also can be used in high radiation dose condition and other dangerous radiation occasions.

Real-time fibre optic radiation dosimeters for nuclear environment monitoring around thermonuclear reactors

The ability of fibre optic sensors to operate in hazardous nuclear environments and their intrinsic immunity to electro-magnetic interference make fibre optic sensing a very promising technology for the future ITER thermonuclear fusion reactor. In this paper, we evaluate fibre optic sensing technology for monitoring radiation dose in the vicinity of ITER during its operation and during the maintenance periods. First, the performance of an OSL dosimeter interrogated remotely using radiation tolerant optical fibres is evaluated both for real-time and integrating measurements for doses exceeding 100 Gy. We demonstrate its satisfactory operation in a mixed gamma neutron field. Second, we discuss the successful calibration of a new scintillating fibre optic radiation probe based on CsI(TI) crystals for operation in the dose-rate range 0.3–3000 mGy/h. The CsI(TI) crystal scintillator is mounted at the end of a 10-m long multimode fibre transceiver link to allow for remote deployment. The probes can detect and measure gamma dose rates ranging from 1 to 1000 mGy/h. Finally, we investigate the possible use of commercially available PMMA plastic optical fibres as on-line dosimeters up to 34 kGy. The dose measurement is derived from the radiation-induced attenuation in the optical fibre itself. A novel interrogation scheme based on a ratiometric technique is proposed for real-time dosimetry.

Thermal focusing of radiation in optical fibers

The influence of external thermal factors on optical fibers is considered. The phenomenon of periodic breakdown observed in gradient-index fibers can be explained by radiation focusing, by which the intensity can grow up to a level sufficient to produce damage of the core material.

MO‐E‐L100J‐03: Development of a Novel Electronic Portal Imaging Device Based On Cherenkov Radiation

Purpose: Most electronic portal imaging devices (EPIDs) developed so far use a Cu plate/phosphor screen to absorb x rays. The main problem with this approach is that the Cu plate/phosphor screen must be thin (∼ 2 mm) in order to obtain a high spatial resolution, resulting in a low quantum efficiency (QE) for megavoltage (MV) x rays (typically 2–4%). In addition, the phosphor screen contains high atomic number (high‐Z) materials, resulting in an over‐response of the detector to low energy x rays in dosimetric verification. Our goal is to develop a new high QE MV x‐ray detector made of a low‐Z material for both geometrical and dosimetric verification in radiotherapy. Method and Materials: Our approach uses radiation‐induced light (Cherenkov radiation) in optical fibers that are made of low‐Z materials. With our approach, a thick (∼ 10–30 cm) fiber‐optic taper consisting of a matrix of optical fibers aligned with the incident x rays is used to replace the thin Cu plate/phosphor screen to dramatically increase the QE. The feasibility of this approach has been investigated using a single optical fiber embedded in a solid material. The spatial resolution expressed by the modulation transfer function (MTF) and the signal‐to‐noise ratio of the proposed detector at low doses (∼ one Linac pulse) have been measured. Results: It is predicted that, using this approach, a detective quantum efficiency (DQE) of an order of magnitude higher at zero frequency can be obtained while maintaining a reasonable MTF, as compared to current EPIDs. Conclusion: This work demonstrated the feasibility of using Cherenkov radiation for portal imaging applications [Work supported by the Individual Discovery Grant Program awarded by National Sciences and Engineering Research Council of Canada (NSERC)].

Transmission of Čerenkov radiation in optical fibers

Cerenkov radiation is generated as an unwanted background when optical fibers carrying signals pass through radiation fields. The angular dependence of the intensity of ? Cerenkov radiation transmitted in silica-core fibers was measured using 6 and 12 MeV electron beams from a Varian Clinic accelerator. These confirmed theoretical predictions that the angular variation of ? Cerenkov radiation transmitted along optical fibers depends only on the refractive index difference Dn between the core and the cladding, and that the peak intensity is proportional to the cube of the fiber core radius.

Far-field radiation of optical fibers with tapered end

In this paper, an accurate model of the far-field radiation of a tapered optical fiber, which is widely used in communication optics and biomedical tomography, is presented. The authors first analyze the far field that is radiated from the normally cut fiber then extend the model to a fiber with a tapered end by considering the different phase contributions of the emitted rays. The proposed technique shows the effects of the cut with a view of obtaining a high efficiency both in coupling and radiation pattern characteristics

Gamma ray radiation induced absorption in Ti doped single mode optical fibres at low dose levels

Induced loss due to optical absorption of single mode optical fibres doped with TiO 2 and GeO 2 + TiO 2 in the silica core glass matrix under 60Co gamma radiation has been studied at different dose rates in the range of 5–10 Gy/h at 1310 nm transmission wavelength for evaluation of their radiation response behaviour. The radiation sensitivity of the fibres due to induced optical absorption of Ti 3+ related colour centers shows considerable variation with Ti content in SiO 2 and SiO 2 + GeO 2 host glass matrix of the core, fibre design and operating wavelength. The maximum sensitivity in visible region was observed at 540 nm absorption wavelength. The recovery nature as well as the effect of photobleaching and thermobleaching phenomena have also been investigated. The high radiation sensitivity along with linear response behaviour, low recovery and almost dose rate independent behaviour of the material system of TiO 2 doped SiO 2 and TiO 2 doped SiO 2–GeO 2 core optical fibres under gamma radiation show their capability for application as fibre optic radiation sensor.

Origin of temporally stable continuous-wave Stokes emission in stimulated Brillouin scattering: evidence of spectral self-phase conjugation

We report results on the appearance of temporally stable Stokes emission in stimulated Brillouin scattering (SBS) excited by continuous-wave pump radiation in optical fiber. With increasing pump strength the stable component emerges from stochastic emission slightly above the SBS threshold to become the dominant contribution, independent of fiber characteristics. These findings are shown to be a manifestation of spectral self-phase conjugation, providing what is to our knowledge the first experimental evidence of this phenomenon in optics.

Dynamics of radiation in optical fibers with a dispersive effective cross-section area of the mode

By using a graded-index optical fiber with a parabolic distribution of the refractive index as an example, it is shown that shock waves of envelopes can arise in optical fibers with a significantly dispersive (frequency-dependent) effective cross-section area of the mode. In principle, the shock wave caused by this dispersion can appear at the leading edge of the wave packet. The possibility of forming soliton pulses in media with a dispersive area of the mode is considered.

An optical fiber radiation sensor for remote detection of radiological materials

This paper demonstrates the feasibility of a portable radiation sensor system that uses the pulsed optically stimulated luminescence technique to remotely interrogate an aluminum oxide (Al/sub 2/O/sub 3/:C) radiation sensor via an optical fiber. The objective is to develop a system for applications requiring simple and inexpensive sensors for widespread monitoring of ionizing radiation levels, which can be remotely interrogated at regular periods with little or no human intervention and are easy to install, operate, and maintain. Results on the optimization and performance of the system are presented. The current minimum detectable dose is of the order of 5 /spl mu/Gy, which is already satisfactory for applications such as the monitoring of radioactive plumes from radioactive waste sites. We also discuss potential developments that could decrease the minimum detectable dose to allow radiation doses as low as the background level to be measured over short time intervals, making the system more versatile for detecting radiological materials.

Sensitivity of plastic scintillating fiber optic for X and γ radiation, a simulation study

This article introduces and gives the basic performance characteristics of an optical fiber radiation sensing system. Some fundamental characteristics of plastic scintillating fiber (PSF) for electromagnetic radiation (X- and γ-ray) in the energy range of 10–400 keV, are studied by using Geant4 simulation package. The main advantages of PSFs are their fast response, flexibility, and electromagnetic immunity. The PSF could be used as a nuclear radiation sensor or a detector for monitoring and imaging purposes. It is shown that the sensitivity of the PSF in low energy is good enough to use it as a pixel of imaging detector. In order to find quantum efficiency (QE), the energy deposition in fiber, the absorption, conversion, as well as the transfer efficiency is simulated.