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Abstract: An efficient erbium–ytterbium-doped fiber amplifier (EYDFA) is demonstrated by forward and backward pumping a 3m erbium/ytterbium co-doped fibers (EYDF) in single- and double-pass configurations using a 20mW pump. At the input signal wavelength of 1536nm, the forward- and backward-pumped double-pass amplifiers achieved a maximum low-signal gain of 37.2 and 28.6dB and a corresponding noise figure of 5.4 and 10.8dB, respectively. Whereas, the forward- and backward-pumped single-pass amplifiers (at the same wavelength) achieved a maximum low-signal gain of 20.0 and 22.2dB and a corresponding noise figure of 4.6 and 10.3dB, respectively. The double-pass design offers an economical solution to high-efficiency and high-gain optical amplifiers. [Copyright &y& Elsevier]

The thermoluminescence (TL) response of Germanium Flat Fiber (GFF) and TLD-100 irradiated with 2.5 MeV electrons for the doses up to 1 MGy were studied and compared. The aim was to evaluate the TL supralinearity response at an ultra-high dose (UHD) range and to investigate the change in kinetic parameters of the glow peaks, as the doses increases up to 1 MGy. It is found that the critical dose limit (CDL) of GFF is 5 times higher as compared to TLD-100. CDL is determined by the dose at the maximum supralinearity, f(D) max . It is also found that annealing the TLD-100 and GFF with temperature more than 400 °C is required to reset it back to its original condition, following radiation doses up to 1 MGy. It is also noticed the strange behavior of Peak 4 (TLD-100), which tends to be invisible at the lower dose (<10 kGy) and starts to be appeared at the critical dose limit of 10 kGy. This result might be an important clue to understand the behavior of TLD-100 at extremely high dose range. For both samples, it is observed that the TL intensity is not saturated within the UHD range studied. [ABSTRACT FROM AUTHOR]

Prime dosimetric properties, including dose–response, linearity with dose, energy response, fading and threshold doses were investigated for three different dimension Ge-doped flat fibers. The results of measurement were also compared with two of the more commonly used standard TLD media, TLD-100 (LiF:Mg,Ti−7.5% 6 LiF) and TLD−700 ( 7 LiF:Mg,Ti−99.9% 7 LiF) chips. The flat cross-section samples (60×180) µm 2 , (100×350) µm 2 and (200×750) µm 2 were fabricated using the Modified Chemical Vapor Deposition (MCVD) process and pulled from the same “preform.” In the study, all flat fiber samples provided good linear dose–response for the photon and electron beams generated using a medical linear accelerator (LINAC), for doses in the range 0.5–8 Gy. Among the samples, the smallest dimension flat fiber provided the best response, with a sensitivity of some 61% and 54%, respectively of that of the TLD-100 and TLD-700 chips. The energy responses of the samples were studied for various photon (6 MV, 10 MV) and electron (6 MeV, 9 MeV) beam energies. TL fading of around 20% was observed over a period of thirty (30) days. These favorable TL characteristics point towards promising development of Ge-doped flat fibers for use in radiotherapy dosimetry. [ABSTRACT FROM AUTHOR]

Important thermoluminescence (TL) properties of five (5) different core sizes Ge-doped optical fibers have been studied to develop new TL material with better response. These are drawn from same preform applying different speed and tension during drawing phase to produce Ge-doped optical fibers with five (5) different core sizes. The results of the investigations are also compared with most commonly used standard TLD-100 chips (LiF:Mg,Ti) and commercial multimode Ge-doped optical fiber (Yangtze Optical Fiber, China). Scanning Electron Microscope (SEM) and EDX analysis of the fibers are also performed to map Ge distribution across the deposited region. Standard Gamma radiation source in Secondary Standard Dosimetry Lab (SSDL) was used for irradiation covering dose range from 1 Gy to 10 Gy. The essential dosimetric parameters that have been studied are TL linearity, reproducibility and fading. Prior to irradiation all samples ∼0.5 cm length are annealed at temperature of 400 °C for 1 h period to standardize their sensitivities and background. Standard TLD-100 chips are also annealed for 1 h at 400 °C and subsequently 2 h at 100 °C to yield the highest sensitivity. TL responses of these fibers show linearity over a wide gamma radiation dose that is an important property for radiation dosimetry. Among all fibers used in this study, 100 μm core diameter fiber provides highest response that is 2.6 times than that of smallest core (20 μm core) optical fiber. These fiber-samples demonstrate better response than commercial multi-mode optical fiber and also provide low degree of fading about 20% over a period of fifteen days for gamma radiation. Effective atomic number ( Z eff ) is found in the range (13.25–13.69) which is higher than soft tissue (7.5) however within the range of human-bone (11.6–13.8). All the fibers can also be re-used several times as a detector after annealing. TL properties of the Ge-doped optical fibers indicate promising applications in ionizing radiation dosimetry. [ABSTRACT FROM AUTHOR]

Pure silica optical flat fibers (FF) have been proposed as the basis for a novel radiation sensor by the measurement of the thermoluminescence (TL) produced. In this paper the TL performance of the FFs were studied. Using a linear accelerator (LINAC) delivering doses in the range 0.2–10.0 Gy, the TL dosimetric glow curves of the FFs were studied with respect to 6 MeV electron and 6 MV photon beams. When exposed to 6 MeV electron irradiation, the pure silica FFs displayed a supralinear response starting from 2 Gy up to 10.0 Gy. While for 6 MV photon irradiation, the FFs shows linear characteristic ( f ( D ) = 1 ) nearly up to 2 Gy. The TL intensity ( I m ) of the main peak of FFs is 1.5 times higher for 6 MeV electron beams than for 6 MV photon beams. The maximum peak temperature ( T m ) it is not affected by the type of irradiation used at the same dose while the maximum TL intensity ( I m ) was found to be dependent on the type of radiation used. Overall results indicate that the pure silica FFs can be used as radiation sensors in the high-dose therapy dosimetry. [ABSTRACT FROM AUTHOR]

The pulse-by-pulse characteristics of electron beams from a clinical linear accelerator (linac) at high dose rates are crucial for ensuring precise dose delivery in radiation therapy. In this research, we employ a radioluminescence scintillator made from Ge-doped silica optical fiber to analyse electron beams at standard therapy dose rates 600 cGy/min with energy of 15 MeV. The scintillator is combined with a photomultiplier tube (PMT) and a photon-counting setup to achieve microsecond (μs) gating times, providing high temporal resolution. For sub-microsecond (sub-μs) temporal resolution, we utilize a multi-pixel photon counter and a rapid digital oscilloscope. Our study examines the peak time and the time it takes for pulses to return to baseline, uncovering the effects of afterglow at elevated dose rates and its potential implications for dosimetry precision. Our results indicate that monitor chambers, which have lower temporal resolution than the radioluminescence system outlined in this study, may struggle to accurately track high-rate dose delivery, emphasizing the necessity for advanced monitoring methods in FLASH radiotherapy. The dosimetric data was further analysed for deeper analytics on a cloud-based system. The dosimetric data underwent advanced analysis on a cloud-based platform, employing a prototype analytics software system comprised of Dosi-Client and Dosi-Cloud Backend components for real-time data acquisition and processing. This innovative approach revealed significant insights into radiation dosimetry, including the detection of anomalies through a reconstruction convolutional autoencoder, enhancing the precision and reliability of dosimetric measurements. • Introduces a radioluminescence optical fiber-based dosimetry system. • It is designed for real-time detection of dose-rate errors. • Ge-doped silica optical fiber scintillator showed successful measurements. • An embedded computer is used for measurement and storage of dosimetry data. • Cloud system provides storage and analysis of the data. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the comparison of using least mean square time-domain equalizer (LMS-TEQ) and decision feedback time-domain equalizer (DF-TEQ) to reduce cyclic prefix (CP) length for direct-detection of optical orthogonal frequency division multiplexing (O-OFDM) over 6960km of single mode fiber (SMF). Both TEQs are used immediately after the channel. Numerical modeling results show that they can cancel the residual inter symbol interference (ISI) and inter carrier interference (ICI) caused by both the group velocity dispersion (GVD) and the CP length being shorter than the channel impulse response (CIR). Using these TEQs allow the reduction of CP length, and consequently leading to system performance improvement. On the other hand, each of TEQs adds complexity to the system. Therefore, the aim of this paper is to analyze and compare the performance of LMS-TEQ and DF-TEQ while considering different CP length and complexity. [Copyright &y& Elsevier]

Abstract: The paper presents an experimental investigation of the gain spectrum of an erbium-doped fiber amplifier (EDFA) considering different system configurations, which include single-pass, double-pass, and double-pass with tunable band-pass filter (TBF). The role of TBF is to suppress the undesired amplified spontaneous emission (ASE). Both co- and counter-pumping schemes are considered with a 1480nm laser diode as the pump and a suitable tunable laser source as the signal source. The results indicate that the signal achieves an average of 14dB higher gain in the case of double-pass amplification with the implementation of a TBF. However, the pumping scheme hardly becomes of much importance in influencing the gain characteristics. [Copyright &y& Elsevier]

Present study concerns the key thermoluminescence (TL) properties of photonic crystal fibres (PCFs), seeking development of alternatively structured TL materials that are able to offer a advantages over existing passive dosimeters. In terms of their internal structure and light guiding properties the PCFs, collapsed and structured, differ significantly from that of conventional optical fibres. To investigate the dosimetric parameters of the PCFs use was made of a linear accelerator producing a 6 MV photon beam, delivering doses ranging from 0.5 Gy to 8 Gy. The parameters studied included TL response, linearity index, glow curves, relative sensitivity and TL signal fading, the results being compared against those obtained using TLD-100 chips. At 4 Gy photon dose the Ge-doped collapsed PCFs were found to provide a response 27 × that of structured PCF, also giving a TL yield similar to that of standard TLD-100 chips. Over post-irradiation periods of 15 and 30 days collapsed PCF TL signal fading were 8% and 17% respectively, with corresponding values of 37% and 64% for the structured PCF. Trapping parameters including the order of kinetics (b), activation energy (E) and frequency factor (s-1) were assessed with Chen's peak shape method. Lifetime of trapping centre was found to be (2.36 E+03) s and (9.03 E +01) s regarding the collapsed and structured PCF respectively with 6 Gy of photon beam. For the Ge-doped collapsed PCF, the high TL yield, sensitivity and low fading provide the basis of a highly promising system of TLD for radiotherapy applications. [Display omitted] • Life time of trapping centre was found to be 2.36E+03 and 9.03E +01 regarding the collapsed and structured PCF respectively. • Collapsed PCF gives rise by far to the greatest TL response, at some 27 × that of the structured PCF. • The relative sensitivity of the Ge-doped collapsed and structured PCF with respect to standard TLD-100 were 0.94 and 0.03 respectively. • During thirty days post irradiation, the Ge-doped collapsed PCF provides minimal fading 17% compared to the 64% loss of the structured PCF. • The respective mean daily losses were 0.6% and 2%. [ABSTRACT FROM AUTHOR]

This study explores the dosimetric potentials of pristine lithium zinc borate, LiZnBO 3 , (LZB) phosphor for medical application. The pristine LZB was synthesized by the solid-state reaction (SSR) technique. The structural properties of the synthesized composites were investigated by X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) measurements. The FT-IR data shows that the functional groups are responsible for the peak intensity of LZB. The magnetic hysteresis (M-H) loop was characterized using Vibrating Sample Magnetometry (VSM) to distinguish its magnetic characteristics and alterations. From the M-H loop, it behaves as a superparamagnetic material. A clinical Linear Accelerator (LINAC) was used to irradiate the samples with both electron (6 MeV) and X-ray photon beam (6 MV), with a dose range of 0.5 Gy–8 Gy for both beams. The experiment was designed to study low to medium-dose TL response for LZB. The irradiated samples were readout for thermoluminescence (TL) signal using a Harshaw-3500 TL reader with a fixed heating rate of 10 °C/s. The TL kinetic parameters of the composites were studied by analysing the glow curves using the peak-shape method. The geometric factor (μ g) is found to be within the range of 0.42–0.52, which indicates the suitability of applying Chen's general-order formula to calculate kinetic parameters. The activation energy (E) is found in the range of 1.13–3.14 eV for 4 deconvoluted peaks of 6 MeV electron beam irradiation and 1.82–2.16 eV for 3 deconvoluted peaks of 6 MV X-ray photon beam irradiation. The frequency factor (s) also increases while activation energy increases for both electron and X-ray photon beams. All the obtained results confirm the suitability of LZB phosphor to develop a viable radiation dosimeter. • This work synthesized LiZnBO3 phosphor by solid state reaction method. • Structural, crystalline and magnetic properties are studied using state-of-the-art techniques. • The phosphor was irradiated by 6 MV and 6 MeV X-ray beam and electron beam, respectively. • TL features and kinetic parameters of this phosphor are studied for dosimetry applications. • Our findings reveal the suitability of using LZB as a passive dosimeter in medical field. [ABSTRACT FROM AUTHOR]

• P-doped silica optical fiber produces radioluminescence under MV X-ray exposure. • Real-time, remote reading achieved through fiber-optic coupled configuration. • Emission is consistent for a particular dose-rate producing flat top response. • Absence of memory effect makes possible successive measurement without annealing. • Integration of radioluminescence photon counts provides reliable estimate of dose. Radiation dosimetry applications related to radiotherapy have clear importance in determining the accurate and safe delivery of patient prescribed doses. Versatile yet robust, high spatial resolutions, wide dynamic range real-time forms of dosimetry are called for. Doped silica optical fibers of sub-mm spatial resolution exhibit useful radioluminescence (RL) properties when exposed to ionizing radiation. In this study, primary investigations have been carried out on phosphorus-doped silica optical-fiber. High-energy clinical X-ray beams (6 MV and 10 MV) were used to irradiate the optical fiber, RL response being recorded for six dose-rates (between 100 MU/min and 600 MU/min) delivered by a Varian 2100 C/D linear accelerator. The P-doped optical-fiber showed linear RL response, with minimal observable memory and afterglow and plateau effects. The results indicate the P-doped optical-fiber dosimeter to have strong potential for use in radiotherapy applications. [ABSTRACT FROM AUTHOR]

Many minerals and compounds show thermoluminescence (TL) properties but only a few of them can meet the requirements of an ideal dosimeter. Several phosphate materials have been studied for low-dose dosimetryin recent times. Among the various phosphates, ABPO 4 -type material shows interesting TL properties. In this study, an ABPO 4 -type (A = Lithium, B=Calcium) phosphor is synthesized using a modified solid-state diffusion method. Temperature is maintained below 800 °C in every step of phosphor preparation to obtain the pure phase of Lithium calcium phosphate (LiCaPO 4). The purpose of this work is to synthesize LiCaPO 4 using a simple method, examine its structural and luminescence properties in order to gain a deeper understanding of its TL characteristics. The general TL properties, such as TL glow curve, dose linearity, sensitivity, and fading, are investigated. Additionally, this study aims to determine various kinetic parameters through Glow Curve Deconvolution (GCD) method using the Origin Lab software together with the Chen model. XRD analysis confirmed the phase purity of the phosphor with a rhombohedral structure. Lattice parameters, unit cell volume, grain size, dislocated density, and microstrain were also calculated from XRD data. Raman analysis and Fourier Transform Infrared analysis were used to collect information about molecular bonds, vibrations, identity, and structure of the phosphor. To investigate TL properties and associated kinetic parameters, the phosphor was irradiated with 6.0 MV (photon energy) and 6.0 MeV (electron energy) from a linear accelerator for doses ranging from 0.5 Gy to 6.0 Gy. For both photon and electron energy, TL glow curves have two identical peaks near 200 °C and 240 °C.The TL glow curves for 0.5 Gy–6 Gy are deconvoluted, then fitted with the appropriate model and then calculated the kinetic parameters. Kinetic parameters such as geometric factor (μ g), order of kinetics, activation energy (E), and frequency factor (s) are obtained from Chen's peak shape method. The dose against the TL intensity curve shows that the response is almost linear in the investigated dose range. For photon and electron energy, the phosphor is found to be the most sensitive at 2.0 Gy and 4.0 Gy, respectively. The phosphor shows a low fading and after 28 days of exposure, it shows a signal loss of better than 3%. The studied TL properties suggest the suitability of LiCaPO 4 in radiation dosimetry and associated fields. • XRD analysis revealed the phase purity of the phosphor (LiCaPO4) with a rhombohedral structure. • TL glow curve of the material showed two identical peaks near 200 °C and 240 °C. • Fading of TL signal of the material was less than 3% for the period of 28 days. • TL intensity provided almost linear response over the dose range from 0.5 Gy to 6 Gy. [ABSTRACT FROM AUTHOR]

Abstract We discuss recent investigations by members of this group concerning the performance of P-doped silica for radioluminescence-based dosimetry. Comparisons are made against that of an in-house developed Ge-doped silica system and carbon-doped alumina (Al 2 O 3 :C). The readout obtained for dose-rate evaluations herein make use of the phenomena of radioluminescence (RL), which is enabled by defects giving rise to electron trapping. We have compared the RL signal originating from our Ge- and P-doped silica optical fibres (doping of Ge and P being the primary sources of defects in the silica media) and commercial nanoDot Al 2 O 3 :C dosimeters, the RL signal being guided through PMMA optical fibres to obtain real-time measurements. In regard to afterglow, the P-doped fibre retains the least memory of prior irradiation, favouring its use in real-time evaluations in the use of pulsed beams, improving upon the performance of the Ge-doped fibre. Highlights • In radioluminescence mode P-doped silica fibres applied in radiotherapy and radiology dosimetry. • Performance compared against Ge-doped silica and Al 2 O 3 :C media. • Build-up and afterglow less than that of Ge-doped and nanoDot Al2O3:C dosimeters. • A range of exposure durations studied, from ns to tens of seconds and beyond. [ABSTRACT FROM AUTHOR]

Abstract In previous work we investigated the real-time radioluminescence (RL) yield of Ge-doped silica fibres and Al 2 O 3 nanodot media, sensing electron- and x-ray energies and intensities at values familiarly obtained in external beam radiotherapy. The observation of an appreciable low-dose sensitivity has given rise to the realisation that there is strong potential for use of RL dosimetry in diagnostic radiology. Herein use has been made of P-doped silica optical fibre, 2 mm diameter, also including a 271 µm cylindrical doped core. With developing needs for versatile x-ray imaging dosimetry, preliminary investigations have been made covering the range of diagnostic x-ray tube potentials 30 kVp to 120 kVp, demonstrating linearity of RL with kVp as well as in terms of the current-time (mAs) product. RL yields also accord with the inverse-square law. Given typical radiographic-examination exposure durations from tens- to a few hundred milliseconds, particular value is found in the ability to record the influence of x-ray generator performance on the growth and decay of beam intensity, from initiation to termination. Highlights • First use is made of radioluminescence (RL) from P-doped silica fibre in tracking the energising of a diagnostic x-ray tube. • Real-time, sensitive detection at sub millisecond temporal resolution obtained. • RL from this small volume sensor has demonstrable potential for use in patient dosimetry and generator performance analysis. [ABSTRACT FROM AUTHOR]

A tunable ring cavity single longitudinal mode (SLM) fiber laser incorporating Gallium-Erbium co-doped fiber (Ga-EDF) gain medium and several mode filtration techniques is demonstrated. With Ga-EDF, high emission power was accorded in short fiber length, allowing shorter overall cavity length and wider free spectral range. Tunable bandpass filter, sub-ring structure, and cascaded dissimilar fiber taper were utilized to filter multi-longitudinal modes. Each of the filter mechanism was tested individually within the laser cavity to assess its performance. Once the performance of each filter was obtained, all of them were deployed into the laser system. Ultimately, the 1561.47 nm SLM laser achieved a narrow linewidth laser, optical signal-to-noise ratio, and power fluctuation of 1.19 kHz, 61.52 dB and 0.16 dB, respectively. This work validates the feasibility of Ga-EDF to attain a stable SLM output in simple laser configuration. [ABSTRACT FROM AUTHOR]

Geant4 is a versatile simulation platform for numerous applications involving transport of ionizing radiation, including ionizing photons. Moreover, the physics needed for tracking optical photons is also embedded in the Geant4 simulation toolkit. From its introduction two decades ago there have been a variety of reports concerning the use of the Geant4 code in optical photons transport applications. Further to this, in particular for the interests herein, characterizations of radioluminescence radiation detectors have also been conducted. Noting the rapid development of such detectors, reliant on light collection and detection, there has been an implicit need for optimization of the different components forming the respective optical devices. Compared to ionizing radiation transport modeling less attention has been paid to this capability among the radiation physics community and Geant4 users. This review first describes in brief terms the physics built into Geant4 to provide for the transport of optical photons. This is followed by a retrospective on reported applications, discussion of the strengths and deficiencies of optical transport analyses by Geant4 and contemplation of possible future applications. • Geant4 simulation platform also has the capability to simulate optical photons besides simulating the ionizing photons. • Description of Geant4 physics for transport of optical photons and ionizing photons. • Current and potential applications simulated using Geant4 for tracking optical photons. • Strengths and deficiencies of optical transport analyses by Geant4. [ABSTRACT FROM AUTHOR]

In thermoluminescence (TL) material dopant concentration has an important effect on their characteristics as a “radiation-sensor”. The study investigates dosimetric properties of four different concentration (4 mol%, 5 mol%, 7 mol% and 25 mol%) tailor-made Ge-doped silica fibers. The intention is to seek development of alternative TL materials that offer exceptional advantages over existing passive systems of dosimetry, including improved spatial resolution, a water impervious nature and low cost. Photon beams (6 MV and 10 MV) from a clinical linear accelerator were used for irradiation of the fiber samples over radiation therapy doses, ranging from 0.5 Gy to 8 Gy. SEM-EDX analysis was also performed to investigate the homogeneity of distribution of Ge dopant concentration from the fiber samples. The results of measurement were also compared with two of the more commonly used standard TLDs, TLD-100 (LiF: Mg,Ti-7.5% 6 LiF) and TLD-700 (( 7 LiF: Mg,Ti-99.9% 7 LiF) chips respectively. The TL intensity of the fiber samples was found to strongly depend on Ge dopant concentration, with samples showing enhanced TL yields with decreasing Ge dopant concentration. 4 mol% Ge-doped silica fiber provided the greatest response whereas the 25 mol% samples showed the least, indicative of the well-known concentration quenching effects All fiber TLDs provided linear dose response over the delivered radiotherapy dose-range, the fibers also showing a weak dependence on photon beam energies in comparing the TL yields at 6 and 10 MV. The fading behavior of the different concentration Ge doped TLD-materials were also measured over a period of thirty (30) days subsequent to irradiation. The relative sensitivity of the samples with respect to standard TLD-100 were found to be 0.37, 0.26, 0.13 and 0.02 in respect of the 4, 5, 7 and 25 mol% fibers. The primary dosimetry peak, which was by far the most prominent of any other feature covered by the glow curve, was found to be around 244 °C using the most sensitive silica fiber. The study is expected to pave the way in making more comprehensive investigations aimed at defining improved TL response fiber samples. [ABSTRACT FROM AUTHOR]

Various tailor-made doped-silica optical fibres are investigated as dosimeters in support of radiotherapy, based on radioluminescence (RL) and optically stimulated luminescence (OSL) technology. Investigations focus on the development of these glassy dosimetric media, offering a number of advantages going well beyond their water impervious nature and excellent spatial resolution (∼few microns). An RL/OSL photomultiplier-tube (PMT)-based reader was assembled, providing for study of the influence on the RL/OSL signal of different Ge-dopant concentrations (3.59, 4.74 and 7.03 wt%) in silica fibres exposed to medical LINAC photon beams. Among the three arbitrary choices of dopant concentration, those fibres containing the least concentration of Ge (3.59 wt%), denoted as Ge-1, gave rise to the greatest RL yield, at 1.67 and 2.34 times that of Ge-2 (fibres Ge-doped at 4.74 wt%) and Ge-3 (fibres Ge-doped at 7.03 wt%) respectively, reducing in yield with increasing Ge-dopant concentration. At 7.3 × 10 3 counts Gy −1 min at 22 °C, the Ge-1fibres provided the superior sensitivity, also being found to be reusable without noticeable variation in RL signal (<1%; 1 SD) for X-ray exposures delivered at a dose-rate of 600 cGy/min. The RL signal was found to be free from spectral superposition or noise, also exhibiting energy independence in the use of X-rays generated at 6- and 10 MV. In regard to percentage depth-dose (PDD), in measurements made using optical fibre dosimeters and 6 MV X-ray photon beams, the maximum value of PDD, d max , was obtained at a depth of 1.5 cm, in accord with ionization chamber measurements. Using green stimulation light, for all three concentrations of Ge-dopant, linearity between the OSL signal and dose was observed across the 0.5- to 8 Gy dose range investigated. Results from this ongoing study are intended to assist in efforts towards improving the performance of RL/OSL fibre sensors for radiotherapy dosimetry. [ABSTRACT FROM AUTHOR]

This work addresses purpose-made thermoluminescence dosimeters (TLD) based on doped silica fibres and sol–gel nanoparticles, produced via Modified Chemical Vapour Deposition (MCVD) and wet chemistry techniques respectively. These seek to improve upon the versatility offered by conventional phosphor-based TLD forms such as that of doped LiF. Fabrication and irradiation-dependent factors are seen to produce defects of differing origin, influencing the luminescence of the media. In coming to a close, we illustrate the utility of Ge-doped silica media for ionizing radiation dosimetry, first showing results from gamma-irradiated Ag-decorated nanoparticles, in the particular instance pointing to an extended dynamic range of dose. For the fibres, at radiotherapy dose levels, we show high spatial resolution (0.1 mm) depth-dose results for proton irradiations. For novel microstructured fibres (photonic crystal fibres, PCFs) we show first results from a study of undisturbed and technologically modified naturally occurring radioactivity environments, measuring doses of some 10 s of μGy over a period of several months. [ABSTRACT FROM AUTHOR]

Using six types of tailor-made doped optical fibres, we carry out thermoluminescent (TL) studies of X-rays, investigating the TL yield for doses from 20 mGy through to 50 Gy. Dosimetric parameters were investigated for nominal 8 wt% Ge doped fibres that in two cases were co-doped, using B in one case and Br in the other. A comparative measurement of surface analysis has also been made for non-annealed and annealed capillary fibres, use being made of X-ray Photoelectron Spectroscopy (XPS) analysis. Comparison was made with the conventional TL phosphor LiF in the form of the proprietary product TLD-100, including dose response and glow curves investigated for X-rays generated at 60 kVp over a dose range from 2 cGy to 50 Gy. The energy response of the fibres was also performed for X-rays generated at peak accelerating potentials of 80 kVp, 140 kVp, 250 kVp and 6 MV photons for an absorbed dose of 2 Gy. Present results show the samples to be suitable for use as TL dosimeters, with good linearity of response and a simple glow curve (simple trap) distribution. It has been established that the TL performance of an irradiated fibre is not only influenced by radiation parameters such as energy, dose-rate and total dose but also the type of fibre. [ABSTRACT FROM AUTHOR]

In studies focusing on the practice of clinical computed tomography (CT) a particular concern has been that of delivering unnecessary dose to patients and with it the added risk for radiation-induced cancers. For a CT system, present work has investigated the dosimetric characteristics of a Ge-doped optical fiber real-time dosimetry system (model LS-2000, Lumisyns), measuring beam quality, exposure linearity and exposure duration accuracy. For comparison, the study has used a RaySafe X2 test device (Unfors RaySafe) and a Black Piranha (RTI) QA meter. Irradiations were made using a Somatom Definition Flash dual-source 128-slice CT scanner (Siemens Healthcare). The LS-2000, RaySafe X2, and Black Piranha sensors were exposed to beams energized at accelerating potentials ranging from 80 to 140 kVp, with tube current-time products from 50 to 300 mA, and exposure durations from 750 to 2000 ms. Constant signal responses from the LS-2000 have been obtained, measured in respect of beam quality, exposure linearity, and time accuracy. In respect of accuracy of beam quality, the RaySafe X2 and Black Piranha maximum deviations were 1% and 5%, respectively; the coefficients of linearity of RaySafe, Black Piranha and LS-2000 are 1%, 0.4% and 1.4%, respectively; the maximum deviation for the time accuracy test for the three sensors are 0.5%, 2% and 1.3%, respectively. Evaluation of the LS-2000 real-time dosimetry system with a Ge-doped optical fiber scintillator points to potential for its use in clinical CT dosimetry. • We investigate the real-time Ge-doped for clinical computed tomography (CT). • The comparison has been made used of Unfors and RTI QA meters. • The beam quality, exposure linearity and exposure duration accuracy were established. • The LS-2000 shows good potential for use in Clinical CT dosimetry. [ABSTRACT FROM AUTHOR]

Time-resolved radiation dosimetry is an important factor in ensuring dose delivery during radiotherapy is within the prescribed doses for treatment. One method for time-resolved radiation dosimetry is by radioluminescence (RL) measurement technique using doped-silica optical fibre scintillators. The benefits of RL measurement technique include the capability to measure in real-time, high spatial resolution, and greater adaptability. Additionally, time-resolved dosimetry can be achieved by employing suitable scintillators with short rise and decay time. Silica optical fibre scintillators when doped with suitable dopants, provides the temporal resolution required for pulse-by-pulse dosimetry. Yttrium Aluminium Garnet (YAG) crystal optical fiber doped with Cerium and Terbium are discussed as a possible scintillator for time-resolved radiation dosimetry. The Cerium and Terbium co-doped YAG crystal scintillator samples are irradiated under a 6 MV photon beam from a Elekta Synergy® LINAC. The irradiation doses ranged from 100 cGy/min to 600 cGy/min. The measurements were made using an RL system with a gating time of 1μs. Linear RL response to dose of the irradiated scintillator samples was shown with minimal detectable memory, no afterglow or plateau effects. A rise time of 189.3 ns and a decay time of 260 ns were recorded, indicating promising potential for time-resolved radiation dosimetry. • Investigation is made of time-resolved radiation dosimetry using Ce/Tb:YAG fibre. • Linear Radioluminescence response to doses ranging from 100 cGy to 600 cGy. • Good temporal resolution with rise time of 189.3 ns and a decay time of 260 ns. [ABSTRACT FROM AUTHOR]

Using irradiated doped-silica preforms from which fibres for thermoluminescence dosimetry applications can be fabricated we have carried out a range of luminescence studies, the TL yield of the fibre systems offering many advantages over conventional passive dosimetry types. In this paper we investigate such media, showing emission spectra for irradiated preforms and the TL response of glass beads following irradiation to an 241 Am–Be neutron source located in a tank of water, the glass fibres and beads offering the advantage of being able to be placed directly into liquid. The outcomes from these and other lines of research are intended to inform development of doped silica radiation dosimeters of versatile utility, extending from environmental evaluations through to clinical and industrial applications. [ABSTRACT FROM AUTHOR]

We examine the influence of elevated dopant concentration on the thermoluminescence characteristics of novel Ge-doped silica fibres. Basic dosimetric characteristics of the TL media were obtained, including linearity, reproducibility, energy dependence, fading, minimum detectable dose and glow curve analysis, use being made of a 60 Co gamma irradiation facility (mean energy 1.25 MeV) and an electron linear accelerator producing photons at an accelerating potential of 6 and 10 MV. The 6 mol% Ge-doped fibres were found to provide TL response superior to that of 8- and 10 mol% Ge-doped fibres, both for fibres with outer diameter of 241 µm and 604 µm. Concerning reproducibility, obtained under three different test conditions, at <10% the 6 mol% Ge dopant concentration was observed to provide the superior coefficient of variation (CV). In regard to energy dependence, the 10 mol% Ge doped cylindrical fibres produced the largest gradient values at 0.364 and 0.327 for the 241 µm and 604 µm diameter cylindrical fibres respectively and thus the greatest energy dependency. Measured 33 days post irradiation; the 6 mol% Ge doped cylindrical fibres showed the least TL signal loss, at 21% for the 241 µm cylindrical fibre and <40% for the 604 µm cylindrical fibres. The results also revealed that the 6 mol% optical fibres provided the lowest minimum detectable dose, at 0.027 Gy for 6 MV photon beams. Evaluations of these characteristics are supporting development of novel Ge-doped optical fibres for dosimetry in radiotherapy. [ABSTRACT FROM AUTHOR]

Real-time dosimetry plays an important role for accurate patient-dose measurement during radiotherapy. A tiny piece of laboratory fabricated Ge-doped optical fiber has been investigated as a radioluminescence (RL) sensor for real-time dosimetry over the dose range from 1 Gy to 8 Gy under 6 MV photon beam by LINAC. Fiber-coupled software-based RL prototype system was used to assess essential dosimetric characteristics including dose response linearity, dose rate dependency, sensitivity, repeatability and output dependence on field sizes. The consistency level of RL photon counts versus dose rate was also compared with that of standard Al 2 O 3 :C chips. Sensitivity of Ge-doped fiber were found to be sufficiently sensitive for practical use and also provided linear dose responses for various dose rates from 100 cGy/min to 600 cGy/min using both 6 MV photon and 6 MeV electron beams. SEM-EDX analysis was performed to identify Ge-dopant concentration level within the optical fiber RL material. Accumulated doses were also estimated using simple integral technique and the error was found to be around less than 1% under dissimilar dose rates or repeat measurements. The evaluation of the Ge-doped optical fiber based RL dosimeter system indicates its potential in medical dosimetry. [ABSTRACT FROM AUTHOR]

A new method of soot deposition to improve the characteristics of a solution-doped optical fibre preform is reported. The soot was generated using a modified chemical vapour deposition (MCVD) technique. A better longitudinal uniformity of the core refractive index profile and a higher degree of dopant incorporation were obtained when two layers of soot were deposited in the core. These improvements were further extended by depositing each layer at different temperatures. A variation of 0.15 × 10 − 2 (%RSD 3.5%) in the refractive index difference along 23 cm of the preform and a core-to-cladding refractive index difference of approximately 0.012 were achieved using a 1.2 M AlCl 3 solution. [ABSTRACT FROM AUTHOR]

Over the past three decades growing demand for individualized in vivo dosimetry and subsequent dose verification has led to the pursuit of newer, novel and economically feasible materials for dosimeters. These materials are to facilitate features such as real-time sensing and fast readouts. In this paper, purposely composed SiO 2 :Ge optical fiber is presented as a suitable candidate for dosimetry. The optical fiber is meant to take advantage of the RL/OSL technique, providing both online remote monitoring of dose rate, and fast readouts for absorbed dose. A laboratory-assembled OSL reader has been used to acquire the RL/OSL response to LINAC irradiations (6 MV photons). The notable RL characteristics observed include constant level of luminescence for the same dose rate (providing better consistency compared to TLD-500), and linearity of response in the radiotherapy range (1 Gy/min to 6 Gy/min). The OSL curve was found to conform to an exponential decay characteristic (illumination with low LED source). The Ge doping resulted in an effective atomic number, Z eff , of 13.5 (within the bone equivalent range). The SiO 2 :Ge optical fiber sensor, with efficient coupling, can be a viable solution for in vivo dosimetry, besides a broad range of applications. [ABSTRACT FROM AUTHOR]

In regard to thermoluminescence (TL) applied to dosimetry, in recent times a number of researchers have explored the role of optical fibers for radiation detection and measurement. Many of the studies have focused on the specific dopant concentration, the type of dopant and the fiber core diameter, all key dependencies in producing significant increase in the sensitivity of such fibers. At doses of less than 1 Gy none of these investigations have addressed the relationship between dose response and TL glow peak behavior of erbium (Er)-doped silica cylindrical fibers (CF). For x-rays obtained at accelerating potentials from 70 to 130 kVp, delivering doses of between 0.1 and 0.7 Gy, present study explores the issue of dose response, special attention being paid to determination of the kinetic parameters and dosimetric peak properties of Er-doped CF. The effect of dose response on the kinetic parameters of the glow peak has been compared against other fiber types, revealing previously misunderstood connections between kinetic parameters and radiation dose. Within the investigated dose range there was an absence of supralinearity of response of the Er-doped silica CF, instead sub-linear response being observed. Detailed examination of glow peak response and kinetic parameters has thus been shown to shed new light of the rarely acknowledged issue of the limitation of TL kinetic model and sub-linear dose response of Er-doped silica CF. [ABSTRACT FROM AUTHOR]

The behavior of Ge doped silica, SiO 2 flat fibers (FF) irradiated with 2.5 MeV electron radiation at ultra-high dose (UHD) range, up to 1 MGy, has been investigated. The analyzed glow curves measured by the usage of the WinREMS software revealed that peak height and glow curve maximum temperature are highly dependent on the dose. The shape of the glow curves is constant with increasing dose. The supralinearity of all glow peaks increases to its f ( D ) max , which occurs around 50 kGy. No saturation occurs at f ( D ) max and further increases in dose, up to 1 MGy, exhibits a significant decrease in f ( D ). The glow peaks 2 (230 °C) and 4 (290 °C), deconvoluted by the usage of WinGCF software, are the first-order kinetic peaks and can be used as the main dosimetric peaks for high-dose measurements between 1 and 50 kGy in an industrial environment. [ABSTRACT FROM AUTHOR]

The thermoluminescence (TL) glow curves and kinetics parameters of Thulium (Tm) doped silica cylindrical fibers (CF) are presented. A linear accelerator (LINAC) was used to deliver high-energy radiation of 21 MeV electrons and 10 MV photons. The CFs were irradiated in the dose range of 0.2–10 Gy. The experimental glow curve data was reconstructed by using WinREMS. The WinGCF software was used for the kinetic parameters evaluation. The TL sensitivity of Tm-doped silica CF is about 2 times higher as compared to pure silica CF. Tm-doped silica CF seems to be more sensitive to 21 MeV electrons than to 10 MV photons. Surprisingly, no supralinearity was displayed and a sub-linear response of Tm-doped silica CF was observed within the analyzed dose range for both 21 MeV electrons and 10 MV photons. The Tm-doped silica CF glow curve consists of 5 individual glow peaks. The E a of peak 4 and peak 5 was highly dependent on dose when irradiated with photons. We also noticed that the electron radiation (21 MeV) caused a shift of glow peak by 7–13 °C to the higher temperature region compared with photons radiation (10 MV). Our Tm-doped fibers seem to give high TL response after 21 MeV electrons, which gives around 2 times higher peak integral as compared with 10 MV photon radiation. We concluded that peak 4 is the first-order kinetic peak and can be used as the main dosimetric peak of Tm-doped silica CF. [ABSTRACT FROM AUTHOR]

A new method of tuning a multi-wavelength Brillouin-erbium fiber laser (BEFL) within a Fabry–Perot cavity by incorporating a low-cost biconic tapered fiber is reported. The biconic tapered fiber was fabricated using a flame elongation technique and it was incorporated into the BEFL system to position the self-lasing cavity modes over a tuning range of 5.5 nm within the erbium-doped fiber gain profile. By injecting the Brillouin pump near to the tunable self-lasing cavity modes, it suppresses the modes and generates stable cascaded Brillouin–Stokes lines with more than 20 dB signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

Abstract: An efficient erbium/ytterbium co-doped fiber amplifier (EYDFA) is demonstrated by using a dual-stage partial double pass structure with a band pass filter (BPF). The amplifier achieves the maximum small signal gain of 56dB and the corresponding noise figure of 4.66dB at 1536nm with an input signal power and total pump power of −50dBm and 140mW, respectively. Compared with a conventional single-stage amplifier, the maximum gain enhancement of 16.99dB is obtained at 1544nm with the corresponding noise figure is improved by 2dB. The proposed amplifier structure only uses a single pump source with a partial double pass scheme to provide a high gain and dual-stage structure to provide the low noise figure. [Copyright &y& Elsevier]

Abstract: An efficient fluoride-based thulium-doped fiber amplifier (TDFA) is theoretically demonstrated using a double-pass scheme. A reflector is incorporated in the double-pass TDFA to allow double propagation of the test signal in the gain medium and thus improve the gain of the TDFA. The small signal gain improvement of more than 15dB is obtained in the 1465nm region. A gain as high as 42dB is obtained in this region with 300mW of 1050nm pump using 20m of thulium-doped fiber. However, a noise figure penalty of approximately 1dB is also obtained in this wavelength region. Differential equations are solved using the Runge–Kutta method in the theoretical analysis. The theoretical result is in agreement with the experimental result. [Copyright &y& Elsevier]

Time-resolved radiation dosimetry in radiotherapy helps determine the quality of delivery of patient prescribed doses. Earlier reports on doped silica optical fibres as scintillators in radioluminescence (RL) based radiation dosimetry have indicated particular merits, including versatility, robustness, high spatial resolution, wide dynamic range, and the ability for real-time measurements. Time-resolved radiation dosimetry requires high temporal resolution, enabled using a suitable scintillator and high-speed electronics. We report on the potential of Ge-doped optical fibres as a suitable scintillator to be adopted for use in a time-resolved radiation dosimetry system. High-energy clinical X-ray beams (6 MV) were used to irradiate the Ge-doped optical fibre samples. RL responses were recorded for six dose-rates (between 100 MU/min and 600 MU/min) delivered by a Varian 2100 C/D linear accelerator. The photon-counting circuit gating time was set at its shortest capability of 100 μs? The Ge-doped optical-fibre scintillator showed linear RL response, with minimal observable memory and afterglow and plateau effects. The fluorescence lifetime analysis, demonstrate a calculated rise time of 590.1 ns and a decay time of 0.423 μs, indicating superior performance compared to other scintillator forms. These results demonstrate the potential for the Ge-doped optical-fibre scintillator to be used in a time-resolved radiation dosimetry system. •Manuscript Number: RPC-D-21-00446. •Ge-doped Silica Optical Fiber for Time Resolved Radiation Dosimetry. • Time-resolved radiation dosimetry at 100 μs gating time using Ge-doped Silica Optical Fiber as a scintillator. • Linear response with minimal observable memory and afterglow and plateau effects. • The fluorescence lifetime analysis, demonstrate a calculated rise time of 590.1 ns and a decay time of 0.423 μs. [ABSTRACT FROM AUTHOR]

Dosimetry systems are important in any radiation facility to ensure quality, safety, validation, qualification and quality control of established and new processes, including at industrial radiation facilities. We present a study of silica optical fibre as scintillators for industrial radiation dosimetry using Radioluminescence (RL). The RL technique provides for a remote and real-time dosimetry measurement in such a high dose environment. This study establishes the dosimetric characteristics of two variants of pure silica optical fibre, low and high hydroxyl (OH) when exposed to industrial radiation levels. The samples were exposed to a linear accelerator, with doses in the order of tens of kGy (from 10 kGy through to 70 kGy in individual exposures). The performance parameters observed during the study include the RL emission spectrum, emission intensity and emission linearity with exposure dose. The RL spectrum demonstrated a central wavelength of 650 nm and 550 nm for the high and low OH scintillators, respectively. RL intensity was observed to increase with exposed dose, a result of recombination of ionizing radiation generated electron-hole pairs. The RL intensity relation with exposed dose indicated a linear response, with the higher OH sample showing the greater slope, indicating greater sensitivity. The overall results indicate the potential use of pure silica optical fibre as scintillators for remote and real-time industrial radiation dosimetry. • Real-time radiation dosimetry for industrial radiation using fiber optic coupled scintillators. • Pure silica optical fiber scintillators. • Higher sensitivity for high-OH pure silica fiber. • Probe is intrinsically safe, and resistant to water and electromagnetic interference. [ABSTRACT FROM AUTHOR]

Currently existing low-level gamma-ray monitoring and measurement devices in the oil and gas and minerals beneficiations industries have several operational limitations, typically including an inability to be operated in an intrinsically safe mode, restrictions in making remote measurements, and an inability to operate in aqueous or high temperature environments. Herein, characterization is made of an optical fiber system based on a LYSO:Ce scintillator, investigated at dose rates and contamination levels comparable to that in dealing with NORM. The measurements were calibrated against a Geiger Muller (GM) pancake counter. The scintillators produce radioluminescence (RL), propagating in the optical fiber waveguide to the photodetection system, providing real-time, remote and intrinsically safe radiation measurements of NORM and other low-level gamma emissions. The response has been found to be dependent on the orientation of the scintillator axis with respect to the source centre. The LYSO:Ce scintillator has been found to be responsive to naturally radioactive sources, tested using monazite and xenotime offering in-contact dose rates down to 20 μSv/h. The measurements were found to be comparable to that of the GM based measurements, further providing intrinsically safe RL remote capabilities, the study pointing to the potential use of scintillation based optical fiber dosimetry systems for NORM and low gamma-ray level measurement in a variety of industrial scenarios. • Fiber optic coupled radiation sensor for NORM sample dose rate measurement. • Sub-cm LYSO:Ce scintillator diameter. • Sensitivity of 45 cpm/μSv/h during remote measurements (Cs-137). • Probe is intrinsically safe, and resistant to water and electromagnetic interference. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new enhanced design of fibre Bragg grating for flattening the gain profile of an erbium-doped fibre amplifier in transmission configuration. This grating has modulation of refractive index change and constant chirp rate, wherein both profiles of the parameters are properly apodized. The design utilizes an alternative approach to the renowned inverse scattering method, yet produces a similar spectral response quality and conceptually simpler. Moreover, it offers precise control over all parameters of the grating structure. It is shown that the design approach could produce gain-flattening filters of satisfactory quality through simulations using the accurate transfer matrix method. [Copyright &y& Elsevier]

We present time-resolved radioluminescence (RL) measurements from P-doped silica optical fibre, demonstrating potential utility in pulsed source dosimetry. When subjected to 140 MU/min from a 6 MV photon linac source, a 220 µm-core fibre has produced a RL response of 720 ± 20 photon counts/pulse from a saw-tooth ~ 40 µs duration return-to-baseline waveform. Conversely, the Cerenkov stem signal within the radiation insensitive carrier fibre is observed to offer an amplitude amounting to a little less than 3% of that of the P-doped fibre, the sharply spiked response being of ~ 2 µs duration. On the basis of these results, the practical applications and the challenges in the establishment of an effective dosimetry system are discussed. • Time-resolved radioluminescence measurements made of pulsed clinical linac. • Used P-doped silica optical fibre, characteristic ~ 40 µs return to baseline waveform. • ~ 2 µs duration Cerenkov stem signal in carrier PMMA < 3% of P-doped fibre response. • Applied to 6- and 10 MV linac settings, 70–580 MU/min, PRF range 50–400 Hz. [ABSTRACT FROM AUTHOR]

Application-viable yields of optically stimulated luminescence (OSL) are known to be provided by a number of materials, Al 2 O 3 :C nanoDot OSLDs being one of those currently favoured, dominating the world of commercial passive radiation dosimetry. Associated with the use of such materials is the need for versatile, high performance readout devices, opportunities remaining for novel developments in support of the OSL media, as emphasised herein. Present study focuses on the data acquisition capability of an in-house prototype OSL reader, luminescence stimulation being provided by a 30 mW green LED light (spectral mid-point ~ 515 nm). In providing for the additional versatility of making stand-off (at a distance) measurements, the dosimeter sensors (nanoDot OSLD chips) were attached to a polymethyl-methcrylate (PMMA) fibre cable, allowing characterization of the OSL (phosphorescence) at very low risk. Using this prototype instrument, key OSL features from an Al 2 O 3 :C sensor medium have been captured, excellent quantitative agreement being found between present results and those of others using other readers. One further feature of the current design is that it also allows investigation of the excitation light wavelength dependence of sensor media that could be competitive to Al 2 O 3 :C, there being the additional ability to swap out the OSL sensor, filters and other support components. • Performance of an in-house developed OSL system investigated. • System offers OSL/RL versatility. • Design allows for investigation of excitation wavelength dependence. • The design also allows for at a distance stand-off measurements. [ABSTRACT FROM AUTHOR]

• Fabrication of Ga/Tm-doped silica fiber as the saturable absorber to generate Q-switched fiber laser. • Generation of Q-switched fiber laser with short Ga/Tm-doped silica fiber saturable absorber length of only 10 cm. • Acquisition of Q-switched laser pulses from 39.6 to 53.3 mW pump power. An L-band Q-switched fiber laser was demonstrated using gallium/thulium-doped silica fiber saturable absorber. At 10 cm in length, the saturable absorber generated Q-switched fiber laser at a pump power threshold of 39.6 mW and a central wavelength of 1601.93 nm. Beyond 53.3 mW, a spectrum with a central wavelength at 1602.00 nm was generated. On the other hand, the pulse repetition rate was obtained from 3.44 to 7.47 kHz whereas the pulse width reduces from 100.2 to 58.6 µs for pump power ranges from 39.6 to 53.3 mW. Within this range, the pulse energy is attained between 0.2600 and 0.2843 µJ, at a laser power slope efficiency of 6.94%. The constantly operated Q-switched fiber laser over 50 min observation time at 53.3 mW pump power ensures the feasibility of this pulse laser source as a practical device. [ABSTRACT FROM AUTHOR]