The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform

Stuart D. Jackson - One of the best experts on this subject based on the ideXlab platform.

D A Bradley - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of ge doped Silica Fibre tlds for in vivo dosimetry during intraoperative radiotherapy
    Physics in Medicine and Biology, 2019
    Co-Authors: F Moradi, Ghafour Amouzad Mahdiraji, Mayeen Uddin Khandaker, Nur Aishah Taib, D A Bradley
    Abstract:

    : Ge-doped Silica Fibre (GDSF) thermoluminescence dosimeters (TLD) are non-hygroscopic spatially high-resolution radiation sensors with demonstrated potential for radiotherapy dosimetry applications. The INTRABEAM® system with spherical applicators, one of a number of recent electronic brachytherapy sources designed for intraoperative radiotherapy (IORT), presents a representative challenging dosimetry situation, with a low keV photon beam and a desired rapid dose-rate fall-off close-up to the applicator surface. In this study, using the INTRABEAM® system, investigations were made into the potential application of GDSF TLDs for in vivo IORT dosimetry. The GDSFs were calibrated over the respective dose- and depth-range 1 to 20 Gy and 3 to 45 mm from the x-ray probe. The effect of different sizes of spherical applicator on TL response of the Fibres was also investigated. The results show the GDSF TLDs to be applicable for IORT dose assessment, with the important incorporated correction for beam quality effects using different spherical applicator sizes. The total uncertainty in use of this type of GDSF for dosimetry has been found to range between 9.5% to 12.4%. Subsequent in vivo measurement of skin dose for three breast patients undergoing IORT were performed, the measured doses being below the tolerance level for acute radiation toxicity.

  • investigation on various types of Silica Fibre as thermoluminescent sensors for ultra high dose radiation dosimetry
    Sensors and Actuators A-physical, 2018
    Co-Authors: F Moradi, Ghafour Amouzad Mahdiraji, Mayeen Uddin Khandaker, D A Bradley, F Mahamd R Adikan, I Khellaf
    Abstract:

    Abstract With high-dose applications lacking the benefit of an economic yet versatile dosimeter that provides for a wide dynamic dose range, ongoing research is seeking to introduce suitable thermoluminescent (TL) material for such needs. Acknowledging the high potential of Silica Fibres, as developed by members of this group over the past few years, in present work evaluation has been made of 13 types of Fibre, differing in dopant, dopant concentration and diameter including P−, Al−, Er−, Ge− and Al-Tm-doped Fibres, ultra-high numerical aperture and boroSilicate Fibre, and two non-doped Fibres, quartz and suprasil F300. Evaluation is made in terms of TL response to photon and electron irradiations with the objective of determining a TL material that can offer sensitive yet extended dose capability, saturating only above the few tens of kGy range. The various Silica Fibres that have been investigated were found to show saturation levels from 5 kGy for Ge-doped Fibre (4 mol %) to 80 kGy for 2 mol % Al−doped Silica Fibre. BoroSilicate Fibres demonstrated the greatest potential for high dose dosimetry, maintaining a highly-linear response, any tendency towards saturation only being indicated to beyond receipt of doses of 100 kGy. For this Fibre type detailed TL characterizations were conducted, including glow curve analysis, reproducibility and fading tests. The results suggest boroSilicate Fibre to be suitable for high dose TL dosimetry, providing sufficient sensitivity and appropriate dosimetric characteristics.

W.a. Clarkson - One of the best experts on this subject based on the ideXlab platform.

  • Multi-Watt Operation of a Holmium Doped Silica Fibre Laser at 2.2 μm
    2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO Europe-EQEC), 2019
    Co-Authors: L. G. Holmen, J.k. Sahu, P. C. Shardlow, P. Barua, N. Simakov, A. Hemming, W.a. Clarkson
    Abstract:

    Laser sources operating in the atmospheric transmission window between 2.1 and 2.25 μm are of interest for a range of applications (e.g. remote sensing, free-space communication and defence). Holmium Fibre lasers provide good coverage of the lower part of this spectral region [1], but operation towards 2.2 μm is much more challenging due to a reduced emission cross-section and higher propagation losses associated with the IR absorption edge of fused Silica. Furthermore, OH--contamination can cause additional absorption around 2.2 μm. Here we investigate the limits of long-wavelength tuning of a holmium-doped Fibre laser, and report, to the best of our knowledge, the first watt-level (4.1 W) output from a Silica Fibre laser operating at 2.2 μm.

  • Ho-doped Silica Fibre laser in-band pumped by a Tm-doped Fibre laser
    CLEO Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, 2009
    Co-Authors: A. Boyland, J.k. Sahu, W.a. Clarkson
    Abstract:

    In this paper, we report preliminary results for a Ho Silica Fibre laser operating at 2090 nm in-band pumped by a cladding-pumped Tm doped Fibre laser at 1980 nm. The Tm Fibre pump laser was constructed in-house with wavelength selection provided by an external cavity containing a diffraction grating. This could produce over 20 W of output at 1980 nm (corresponding to the absorption peak in Ho-doped Silica) in a beam with M2 ~ 1.5. The Ho-doped Silica Fibre was fabricated in-house and had a Ho-doped alumino-Silicate core of 18 Icircfrac14m diameter and 0.08 NA, which was surrounded by a Silica cladding with a diameter of 300 Icircfrac14m. Pump light at 1980 nm was launched into the core of the Ho Fibre with a launching efficiency of -53 %. Approximately 85% of the launched pump light was absorbed in the 1.5 m length of Ho Fibre used in our experiment. Feedback for lasing was provided by the Fresnel reflection from the perpendicularly cleaved facet at the output end of the Fibre and by a mirror with high reflectivity (>99%) over the wavelength range 2050 to 2150 nm and high transmission (>90%) over the range 1900 - 2000 nm butted to the opposite end of the Fibre. Under these operating conditions, the Ho Fibre laser yielded a maximum output power of 4.3 W at 2090 nm for an absorbed pump power of-8.7 W.

  • ho doped Silica Fibre laser in band pumped by a tm doped Fibre laser
    European Quantum Electronics Conference, 2009
    Co-Authors: A. Boyland, J.k. Sahu, W.a. Clarkson
    Abstract:

    Over the last few years there has been increasing interest in power-scaling of Fibre-based sources operating in the eyesafe two-micron wavelength regime driven by a range of applications. Much of this interest has focussed on Tm-doped Silica Fibres which offer wide spectral coverage from ∼1.7 µm to ∼2.1 µm [1], a range of pump wavelengths and the potential to be scaled to very high powers [2]. By contrast, far less attention has been directed towards Ho-doped Silica Fibres which also offer a very wide range of emission wavelengths extending well beyond 2.1 µm. However, scaling the output power from Ho-doped Silica Fibres is hindered by the fact that there is no absorption band that coincides with the emission wavelengths available from high-power (near-infrared) commercially available diode pump sources. One solution to this problem is to add Tm to the core to act as a sensitiser. In this way pump light from high-power laser diodes at ∼0.8 µm is absorbed by the Tm ions and the Ho ions in-directly excited by energy-transfer from the Tm ions. Using this approach, Jackson et al. recently reported 83 W of output from a cladding-pumped Tm, Ho co-doped Fibre laser [2]. Co-doping with Tm however leads to very strong energy-transfer-upconversion and hence a reduction in the effective upper-state lifetime. The net result is additional heat loading leading, lower efficiency and limited flexibility in mode of operation. An alternative approach is to use a high-power cladding-pumped Tm Fibre laser to pump a Ho-doped Fibre laser avoiding the need for co-doping with Tm [4]. This has the attraction a very low quantum defect pumping scheme can be employed in the Ho Fibre laser allowing very high lasing efficiencies to be achieved and offering the potential to be scaled to very high power levels. In this paper, we report preliminary results for a Ho Silica Fibre laser operating at 2090 nm in-band pumped by a cladding-pumped Tm doped Fibre laser at 1980 nm.

  • power scaling of 2 µm ytterbium sensitised thulium doped Silica Fibre laser diode pumped at 975 nm
    Electronics Letters, 2005
    Co-Authors: Yoonchan Jeong, J.k. Sahu, J. Nilsson, W.a. Clarkson, Deyuan Shen, P Dupriez, Stuart D. Jackson
    Abstract:

    An ytterbium-sensitised thulium-doped Silica Fibre laser that generates up to 75 W of output power in the 2 µm wavelength range when cladding-pumped by a 975 nm diode stack is reported. The slope efficiency is 32% with respect to the launched pump power and the beam quality factor (M2) is 1.3.

  • Power scaling of 2 /spl mu/m ytterbium-sensitised thulium-doped Silica Fibre laser diode-pumped at 975 nm
    Electronics Letters, 2005
    Co-Authors: Yoonchan Jeong, J.k. Sahu, J. Nilsson, W.a. Clarkson, P Dupriez, D.y. Shen, S.d. Jackson
    Abstract:

    An ytterbium-sensitised thulium-doped Silica Fibre laser that generates up to 75 W of output power in the 2 /spl mu/m wavelength range when cladding-pumped by a 975 nm diode stack is reported. The slope efficiency is 32% with respect to the launched pump power and the beam quality factor (M/sup 2/) is 1.3.

Alexander Hemming - One of the best experts on this subject based on the ideXlab platform.

  • Record efficiency of a holmium-doped Silica Fibre laser
    2016 Conference on Lasers and Electro-Optics (CLEO), 2016
    Co-Authors: Alexander Hemming, Nikita Simakov, Michael Oermann, Adrian Carter, John Haub
    Abstract:

    We present a single-mode, 2.09 μm holmium-doped Silica Fibre laser resonantly pumped by a 1.95 μm thulium-doped Fibre laser. The slope efficiency of 87% versus absorbed power is to our knowledge the highest reported to date.

  • a review of recent progress in holmium doped Silica Fibre sources
    Optical Fiber Technology, 2014
    Co-Authors: Alexander Hemming, Nikita Simakov, John Haub, Adrian Carter
    Abstract:

    In this paper we present a review of holmium-doped Silica Fibre based sources. We discuss recent demonstrations of an efficient cladding-pumped Fibre geometry and the impact it has made on the power scaling of these sources. We discuss the wavelength region that is addressable by holmium-doped Silica based devices and highlight the advantage over thulium-doped Fibres in terms of atmospheric transmission. Finally we review the development and current status of the pulsed and CW operation of holmium Fibre sources and discuss the future development potential of sources in the ns-fs pulse-width range.

  • high power operation of cladding pumped holmium doped Silica Fibre lasers
    Optics Express, 2013
    Co-Authors: Alexander Hemming, Shayne Bennetts, Nikita Simakov, John Haub, Alan Davidson, Adrian Carter
    Abstract:

    We report the highest power operation of a resonantly cladding-pumped, holmium-doped Silica Fibre laser. The cladding pumped all-glass Fibre utilises a fluorine doped glass layer to provide low loss cladding guidance of the 1.95 µm pump radiation. The operation of both single mode and large-mode area Fibre lasers was demonstrated, with up to 140 W of output power achieved. A slope efficiency of 59% versus launched pump power was demonstrated. The free running emission was measured to be 2.12-2.15 µm demonstrating the potential of this architecture to address the long wavelength operation of Silica based Fibre lasers with high efficiency.

  • Multiple-watt Tm3+, Ho3+-co-doped Silica Fibre laser tunable across both dopant transitions
    OECC ACOFT 2008 - Joint Conference of the Opto-Electronics and Communications Conference and the Australian Conference on Optical Fibre Technology, 2008
    Co-Authors: Alexander Sabella, Stuart D. Jackson, Alexander Hemming, Shayne Bennetts, David G. Lancaster
    Abstract:

    We have obtained tunable laser emission across both Tm3+ and Ho3+ transitions in a 0.79-mum pumped Tm3+, Ho3+-co-doped Silica Fibre laser. For a 2.3 m Fibre a 1920-2125 nm tuning range was measured with 3.6 W maximum power.

  • A 4W tunable Tm3+:Ho3+ Silica Fibre laser
    2008 Conference on Lasers and Electro-Optics and 2008 Conference on Quantum Electronics and Laser Science, 2008
    Co-Authors: Alexander Hemming, Stuart D. Jackson, Alexander Sabella, Shayne Bennetts, David G. Lancaster
    Abstract:

    A multiwatt Tm3+:Ho3+ co-doped Silica Fibre laser pumped at 0.79 mum is demonstrated with an extended tuning range from 1920-2120 nm, compared with 1880-2040 nm obtained using a Tm3+ only doped Fibre.

Terence A King - One of the best experts on this subject based on the ideXlab platform.

  • Multi-mode 2 μm Tm-Silica Fibre lasers with 1.61 μm in-band pumping
    Journal of Modern Optics, 2007
    Co-Authors: Yuen Hong Tsang, Terence A King
    Abstract:

    In-band pumping of multi-mode Tm-Silica Fibre lasers operating at 2 µm has strong potential due to higher quantum efficiency, increased damage threshold, increased nonlinear threshold and practical larger pumping area. Results are presented on the investigation of multi-mode Tm-Silica Fibre lasers operating near 1.85 µm, containing a high Tm doping concentration of 1.1 wt% (9 × 1025 m−3), when in-band pumped at 1.61 µm near an absorption peak in Tm-Silica. The relationships between lasing performance and Fibre length and cavity losses are reported. The measured highest slope efficiency and threshold achieved are about 42% and 0.4 W obtained with a short optimum Fibre length of 23 cm and cavity reflectivities of (99%–4%), and on a small scale in this configuration a maximum output power of 370 mW was produced. The estimated maximum slope efficiency for the cavity reflectivities of (4%–4%) is up to 56%.

  • self mode locking effects in heavily doped single clad tm3 doped Silica Fibre lasers
    Journal of Modern Optics, 2005
    Co-Authors: F. Z. Qamar, Terence A King
    Abstract:

    Self-mode-locking in single-clad Tm-doped Silica Fibre lasers operating at 1.92 µm is reported with 100% modulated mode-locked pulses observed for longer Fibre lengths up to 6 m. The self-mode-locking was accompanied by self Q-switching. A mode-locked pulse duration of 191 ps has been measured using an autocorrelator based on a two-photon absorption detector for operation at 2 µm assembled for the purpose of this experiment. The experimental pulse train characteristics are found to be consistent with mode-locking theoretical analysis. The origin and properties of self-mode-locking in heavily Tm-doped Fibre lasers are discussed.

  • passive q switching of the tm Silica Fibre laser near 2 μm by a cr2 znse saturable absorber crystal
    Optics Communications, 2005
    Co-Authors: F. Z. Qamar, Terence A King
    Abstract:

    Abstract Q-switching of a single-clad Tm-Silica Fibre laser operating at 1.9 μm is demonstrated using a Cr 2+ :ZnSe saturable absorber crystal. The Q-switching was accompanied by self-mode-locking. A Q-switched pulse duration of 330 ns and peak power of 15 W has been measured for a 1.8 m length Fibre when pumped with 3.6 W launched power at 1.3 μm. The Q-switching process has been optimized for variation of the output coupler reflectively, pump power and Fibre length, and the best performance found for a cavity with 4% output coupler and Fibre length equal to the optimum length for CW operation laser of near 3.2 m.

  • high power 1 9 μm tm3 Silica Fibre laser pumped at 1 09 μm by a yb3 Silica Fibre laser
    Optics Communications, 2004
    Co-Authors: Yuen Hong Tsang, Daniel J Coleman, Terence A King
    Abstract:

    Abstract Wavelength conversion of the Yb 3+ -Silica Fibre laser operating near 1.09 μm has been demonstrated by acting as a direct pump source for a small scale Tm 3+ -Silica Fibre laser to provide an output at 1.9 μm. The characterisation of the Tm 3+ -Silica Fibre laser is described; it operated with a threshold of 30 ± 20 mW, a slope efficiency of 27.2 ± 0.4% with respect to the launched pump power and a maximum output power of 1.1 W. There is evidence of saturation in the output power due to excited state absorption which suggests that the maximum achievable output power of this core-pumped Tm 3+ -doped Fibre laser is approximately 2 W for 1.09 μm pumping.

  • dynamics and self pulsing effects in tm3 doped Silica Fibre lasers
    Optics Communications, 2002
    Co-Authors: Ashraf F Elsherif, Terence A King
    Abstract:

    Abstract Observations are presented on the self-pulsing behaviour of the Tm3+-doped Silica Fibre laser operating near 2 μm. Various self-pulsing regimes are observed for a range of pumping rates when the Fibre is end-pumped with a high power Nd:YAG laser operating at 1.319 μm in a linear bidirectional cavity. A rich variety of nonlinear phenomena, ranging from self-pulsing to self-Q-switching and to a modulated quasi-CW wave, are observed. The phenomenon of pair-induced quenching (PIQ) is considered, compatible with excited-state absorption (ESA). The influence of thulium concentration on ion-pair production is described. The model developed based on the rate equations for a three-level system describes the experimental observations.