The Experts below are selected from a list of 9417 Experts worldwide ranked by ideXlab platform
Franz X Kartner - One of the best experts on this subject based on the ideXlab platform.
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fiber optic Cherenkov Radiation in the few cycle regime
Conference on Lasers and Electro-Optics, 2011Co-Authors: Guoqing Chang, Lijin Chen, Franz X KartnerAbstract:We demonstrate (both theoretically and experimentally) that fiber-optic Cherenkov Radiation in the few-cycle regime exhibits three unique features absent when pumped with long pulses: continuum generation, high conversion-efficiency (up to 40%), and broad bandwidth (70-nm).
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fiber optic Cherenkov Radiation in the few cycle regime
Optics Express, 2011Co-Authors: Guoqing Chang, Lijin Chen, Franz X KartnerAbstract:Fiber-optic Cherenkov Radiation has emerged as a wavelength conversion technique to achieve isolated spectrum in the visible wavelength range. Most published results have reinforced the impression that CR forms a narrowband spectrum with poor efficiency. We both theoretically and experimentally investigate fiber-optic Cherenkov Radiation excited by few-cycle pulses. We introduce the coherence length to quantify the Cherenkov-Radiation bandwidth and its dependence on propagation distance. Detailed numerical simulations verified by experimental results reveal three unique features that are absent when pumped with often-used, long pulses; that is, continuum generation (may span one octave in connection with the pump spectrum), high conversion efficiency (up to 40%), and broad bandwidth (70 nm experimentally obtained) for the isolated Cherenkov Radiation spectrum. These merits allow achieving broadband visible-wavelength spectra from low-energy ultrafast sources which opens up new applications (e.g. precision calibration of astronomical spectrographs).
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highly efficient Cherenkov Radiation in photonic crystal fibers for broadband visible wavelength generation
Optics Letters, 2010Co-Authors: Guoqing Chang, Lijin Chen, Franz X KartnerAbstract:We investigate the dependence of Cherenkov Radiation (CR) on pump pulse parameters and its evolution along the propagation distance. Using a Ti:sapphire laser emitting 10fs pulses as the pump source, we demonstrate highly efficient (>40%), broadband (>50nm) CR in the visible-wavelength range with a threshold energy less than 100pJ and a tuning range over 100nm.
O Scholten - One of the best experts on this subject based on the ideXlab platform.
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a realistic treatment of geomagnetic Cherenkov Radiation from cosmic ray air showers
Astroparticle Physics, 2012Co-Authors: K Werner, Krijn D De Vries, O ScholtenAbstract:We present a macroscopic calculation of coherent electro-magnetic Radiation from air showers initiated by ultra-high energy cosmic rays, based on currents obtained from three-dimensional Monte Carlo simulations of air showers in a realistic geo-magnetic field. We discuss the importance of a correct treatment of the index of refraction in air, given by the law of Gladstone and Dale, which affects the pulses enormously for certain configurations, compared to a simplified treatment using a constant index. We predict in particular a geomagnetic Cherenkov Radiation, which provides strong signals at high frequencies (GHz), for certain geometries together with “normal Radiation” from the shower maximum, leading to a double peak structure in the frequency spectrum. We also provide some information about the numerical procedures referred to as EVA 1.0.
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a realistic treatment of geomagnetic Cherenkov Radiation from cosmic ray air showers
Astroparticle Physics, 2012Co-Authors: K Werner, Krijn D De Vries, O ScholtenAbstract:We present a macroscopic calculation of coherent electro-magnetic Radiation from air showers initiated by ultra-high energy cosmic rays, based on currents obtained from three-dimensional Monte Carlo simulations of air showers in a realistic geo-magnetic field. We discuss the importance of a correct treatment of the index of refraction in air, given by the law of Gladstone and Dale, which affects the pulses enormously for certain configurations, compared to a simplified treatment using a constant index. We predict in particular a geomagnetic Cherenkov Radiation, which provides strong signals at high frequencies (GHz), for certain geometries together with "normal Radiation" from the shower maximum, leading to a double peak structure in the frequency spectrum. We also provide some information about the numerical procedures referred to as EVA 1.0. (C) 2012 Elsevier B.V. All rights reserved.
Guoqing Chang - One of the best experts on this subject based on the ideXlab platform.
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fiber optic Cherenkov Radiation in the few cycle regime
Conference on Lasers and Electro-Optics, 2011Co-Authors: Guoqing Chang, Lijin Chen, Franz X KartnerAbstract:We demonstrate (both theoretically and experimentally) that fiber-optic Cherenkov Radiation in the few-cycle regime exhibits three unique features absent when pumped with long pulses: continuum generation, high conversion-efficiency (up to 40%), and broad bandwidth (70-nm).
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fiber optic Cherenkov Radiation in the few cycle regime
Optics Express, 2011Co-Authors: Guoqing Chang, Lijin Chen, Franz X KartnerAbstract:Fiber-optic Cherenkov Radiation has emerged as a wavelength conversion technique to achieve isolated spectrum in the visible wavelength range. Most published results have reinforced the impression that CR forms a narrowband spectrum with poor efficiency. We both theoretically and experimentally investigate fiber-optic Cherenkov Radiation excited by few-cycle pulses. We introduce the coherence length to quantify the Cherenkov-Radiation bandwidth and its dependence on propagation distance. Detailed numerical simulations verified by experimental results reveal three unique features that are absent when pumped with often-used, long pulses; that is, continuum generation (may span one octave in connection with the pump spectrum), high conversion efficiency (up to 40%), and broad bandwidth (70 nm experimentally obtained) for the isolated Cherenkov Radiation spectrum. These merits allow achieving broadband visible-wavelength spectra from low-energy ultrafast sources which opens up new applications (e.g. precision calibration of astronomical spectrographs).
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highly efficient Cherenkov Radiation in photonic crystal fibers for broadband visible wavelength generation
Optics Letters, 2010Co-Authors: Guoqing Chang, Lijin Chen, Franz X KartnerAbstract:We investigate the dependence of Cherenkov Radiation (CR) on pump pulse parameters and its evolution along the propagation distance. Using a Ti:sapphire laser emitting 10fs pulses as the pump source, we demonstrate highly efficient (>40%), broadband (>50nm) CR in the visible-wavelength range with a threshold energy less than 100pJ and a tuning range over 100nm.
Stephen A Boppart - One of the best experts on this subject based on the ideXlab platform.
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noise characterization of broadband fiber Cherenkov Radiation as a visible wavelength source for optical coherence tomography and two photon fluorescence microscopy
Optics Express, 2014Co-Authors: Youbo Zhao, Yuan Liu, Yuan Zhi Liu, Stephen A BoppartAbstract:Optical sources in the visible region immediately adjacent to the near-infrared biological optical window are preferred in imaging techniques such as spectroscopic optical coherence tomography of endogenous absorptive molecules and two-photon fluorescence microscopy of intrinsic fluorophores. However, existing sources based on fiber supercontinuum generation are known to have high relative intensity noise and low spectral coherence, which may degrade imaging performance. Here we compare the optical noise and pulse compressibility of three high-power fiber Cherenkov Radiation sources developed recently, and evaluate their potential to replace the existing supercontinuum sources in these imaging techniques.
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optical frequency up conversion by supercontinuum free widely tunable fiber optic Cherenkov Radiation
Optics Express, 2009Co-Authors: Stephen A BoppartAbstract:Spectrally-isolated narrowband Cherenkov Radiation from commercial nonlinear photonic crystal fibers is demonstrated as an ultrafast optical source with a visible tuning range of 485–690 nm, which complementarily extends the near-infrared tuning range of 690–1020 nm from the corresponding femtosecond Ti:sapphire pump laser. Pump-to-signal conversion efficiency routinely surpasses 10%, enabling multimilliwatt visible output across the entire tuning range. Appropriate selection of fiber parameters and pumping conditions efficiently suppresses the supercontinuum generation typically associated with Cherenkov Radiation.
Brian D Kavanagh - One of the best experts on this subject based on the ideXlab platform.
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visual sensations during megavoltage radiotherapy to the orbit attributable to Cherenkov Radiation
Medical Physics, 2007Co-Authors: Francis Newman, Masoud Asadizeydabadi, Vikram D Durairaj, M Ding, K Stuhr, Brian D KavanaghAbstract:During megavoltage photon and electron beam radiotherapytreatment involving the eye, patients commonly report visual sensations; “nerve stimulation” is the conventional explanation. We propose that the phenomenon can be attributed to Cherenkov Radiation inside the eye. The threshold electron energy for Cherenkov Radiation in water is 260 keV . The human retina is able to perceive approximately 5–14 visible photons in 0.001 s . A single 500 keV electron traversing 1 mm of water will induce nearly 15 Cherenkov visible range photons. We propose that a portal image involving the eye will produce sufficient Cherenkov Radiation to be detected by the retina.
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tu c aud 01 visual sensations during megavoltage radiotherapy to the orbit attributable to Cherenkov Radiation
Medical Physics, 2007Co-Authors: Masoud Asadizeydabadi, Francis Newman, Vikram D Durairaj, M Ding, K Stuhr, Brian D KavanaghAbstract:Purpose: To compute and to verify experimentally Cherenkov Radiation production inside the eye from direct and indirect high energy x‐ray irRadiation of the orbit and that it exceeds detectability of Cherenkov Radiation in scotopic vision. We show that the Cherenkov yield for direct and indirect irRadiation exceeds the detection threshold of 6.4×107 photons/m2s. Methods: In photon and electron beamradiotherapy of intraorbital and periorbital tissues, patients commonly report having light sensations during treatment. The explanation usually offered is that ‘nerve stimulation’ is occurring. The radiotherapy literature reports the effect to be the result of ‘phosphenes’. Although phosphenes may play a role, we propose instead that patients are predominantly seeing Cherenkov Radiation resulting from electrons inside the eye having kinetic energy exceeding the Cherenkov Radiation threshold of 0.26 MeV. We consider calculations for direct irRadiation of the eye from a portal image and indirect irRadiation from treatment of peri‐orbital tissues and show that it exceeds threshold detection. Results: We calculate the Cherenkov yield using analytic methods and the measurements were in good agreement with our calculations. The Cherenkov Radiation from a distilled water phantom, a square plastic phantom and an anthropomorphic plastic phantom were readily visible with a high quality CCD video camera. A digital camera captures the images from the console monitor. Threshold detection of Cherenkov Radiation emanating from the water phantom through the video camera was determined and compared to a measurable source. The calculations for the water phantom match reasonably well with measurements and are roughly 1 lux and 3 lux respectively. Conclusion: We show images of Cherenkov Radiation emanating from routine radiotherapytreatments and demonstrate that measurements corresponding to these images match well with calculations. We show that the Cherenkov component generated inside ocular media is sufficient to be detected by the patient.