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The High Energy Cosmic Radiation Facility onboard China's Space Station
Available online at www.sciencedirect.com
Nuclear and Particle Physics Proceedings 279–281 (2016) 161–165 www.elsevier.com/locate/nppp
The High Energy Cosmic Radiation Facility onboard China’s Space Station M. Xua , on behalf of the HERD collaboration a Key
Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China
Abstract The High Energy cosmic-Radiation Detection (HERD) facility is one of several space astronomy payloads onboard China’s Space Station, which is planned for operation starting around 2020. It is designed as a next generation space facility focused on indirect dark matter search, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey. HERD is mainly composed of a high granularity cubic calorimeter (CALO) with deep absorption length surrounded by micro-strip silicon trackers (STKs) from five sides, thus maximizing the geometrical acceptance. An overall description of the design will be described. Moreover, R&D is under way for reading out the LYSO signals with optical fiber coupled to image intensified CCD (ICCD) and the prototype of 1/40 CALO for beam test at CERN. Keywords: space experiment, calorimter, cosmic ray, beam test
1. Introduction The steepening power law of the primary cosmic ray (CR) spectrum around several PeV, the so-called knee structure is a classic problem in CR physics as it is related closely to the physics of acceleration and propagation of CRs, but still unresolved[1]. Weakly Interacting Massive Particles (WIMPs) are well motivated candidates of DM particles because they can account for the observed DM density naturally[2]. WIMPs can be detected in CRs through its annihilation into electrons or gamma-rays, resulting in structures to be seen in the otherwise predicted smooth spectra. Some circumstantial evidence or hints of anomalies have been reported[3, 4, 5, 6]; however, astrophysical sources like pulsars and pulsar wind nebulae can also contribute to these results. Experimental data from more precise measurement at higher energies are needed to address the above major problems in fundamental physics and astrophysics. The High Energy cosmic-Radiation Detection (HERD) facility has been planned as one of several space astronomy payloads of the cosmic lighthouse program onboard China’s space station, which is planned http://dx.doi.org/10.1016/j.nuclphysbps.2016.10.023 2405-6014/© 2016 Elsevier B.V. All rights reserved.
for operation starting around 2020 for about 10 years. The main scientific objectives of HERD are: 1) indirect dark matter search through spectra and anisotropy of high energy electrons and gamma-rays from 100 MeV to 10 TeV; 2) precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey from 100 MeV up to 10 TeV. In this paper, we describe the design of HERD and its basic characteristics determined with Monte-Carlo simulations, as well as ongoing R&D efforts in developing HERD prototype for beam test. 2. HERD design and expected performance Our design goal for HERD is simply to optimize its geometrical, absorption depth and its granularity, thus maximizing the acceptance after taking into account the detection and event reconstruction efficiency. To do this, we find that the HERD design with a cubic calorimeter (CALO) of 63 cm×63 cm×63 cm so as to detect particles arriving from every direction in space is required , which is made of nearly 104 pieces of granulated LYSO crystals of 3 cm×3 cm×3 cm each, as illustrated in Fig. 1. From any incident directions, CALO has a minimum
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M. Xu / Nuclear and Particle Physics Proceedings 279–281 (2016) 161–165
Figure 2: Schematic diagram of the ICCD system. The optical taper transmits precisely the image from its input surface coupled with WLS fibers to its output surface which coupled with the image intensifier. And then the signals will be enhanced by the image intensifier and finally collected by the fast and weak light imaging CCD chip.
Please refer to Xu et al (2014) for further details of the simulations[8]. Figure 1: Schematic diagram of the baseline design of HERD. The five sides identical STKs except the bottom for mechanical support, with each side is made of seven layers of silicon micro-strips, sandwiched with tungsten foils, for absolute charge, direction and early shower measurement; the cubic CALO, for energy measurement and provide particle ID information.
stopping power of 55X0 and 3λ, where X0 and λ are radiation and nuclear interaction lengths, respectively. Such a deep and high granularity calorimeter is also essential for excellent electron-proton separation and energy resolutions of all particles. It also has some directional measurement capability with the reconstructed 3D showers. In order to measure the charges and incident directions of cosmic rays, CALO is surrounded by the same seven-layer silicon trackers (STKs) which is made of silicon micro-strip detectors sandwiched with tungsten foils from all five sides except the bottom for mechanical support, to ensure the maximum field of view (FOV) for electrons and gamma-rays. Plastic scintillators surrounding HERD from all five sides are needed to reject most low energy charged particles, in order to have maximum efficiency for high energy cosmic rays and electrons, as well as gamma-rays of all energies. Please refer to Zhang et al (2014) for more details of the requirements and design[7]. Extensive simulations have been carried out with GEANT4 and FLUKA, in order to evaluate the scientific performance of the HERD baseline design. The simulations show that electrons and photons with a high energy resolution (∼ 1% for electrons and photons and 20% for nuclei) and a large effective geometry factor (>3 m2 sr for electrons and diffuse photons and >2 m2 sr for nuclei) can be achieved under this design.
3. Beam Test Objectives The HERD calorimeter prototype is placed in the H4 beam line of the Super Proton Synchrotron (SPS) at CERN in November 2015, and data from proton, electron and fragmentation particles of primary Pb ions on a production target is collected at energies several tens of GeV up to 400 GeV. A key technology of HERD is the signal readout system of the 104 pieces of LYSO crystals with sufficient signal to noise ratio and large dynamical range. In order to minimize the power consumption of readout electronics and heat dissipation inside CALO, we choose to channel the scintillation light out of the LYSO crystals with optical coupling onto CCDs, as illustrated in Fig. 2. The beam test is intended to validate the hardware and software of HERD, and at the same time the beam test have several other major objectives including measurement of the energy resolution, angular resolution, particle identification power and data taking efficiency. As the test beams from the accelerator can only provide particle energies up to 400 GeV which is about several orders of magnitude short of HERD energy range, the response of the detector at higher energies should be carried out by using the extrapolation of Monte Carlo simulation, which means one can verify the precision of said simulations by comparing simulation to measurement at available energies and assess their likely accuracy at higher energies.
M. Xu / Nuclear and Particle Physics Proceedings 279–281 (2016) 161–165
Figure 3: Engineer drawing of the HERD beam test prototype, which including one calorimeter array composed of 250 LYSO crystals, two ICCDs as the readout system of each of the crystal at different energy range, and one self-trigger system which collect signal from all crystals through PMTs.
4. R&D of HERD Calorimeter Prototype for Beam Test The calorimeter prototype is composed of 250 LYSO crystals, two ICCDs and two self-trigger PMTs, as illustrated in Fig. 3. Each crystal with a dimension of 3×3×3 cm3 is contained in a Carbon fiber-reinforced polymer grid, as shown in Fig. 4. The space between crystals is controlled not to be larger than 0.6 mm in the horizontal/vertical direction, respectively. The 5×5×10 crystal array is designed to have the full shower shape contained of the highest SPS electrons beam, which means the main purpose of verifying the specification of electron’s energy resolution can be reached. The uniformity of light output of the crystals have been tested by using a 137 Cs radioactive source in laboratory, results shows that the variation of the crystals are within 25%. Two ICCDs, with the capability of fast and weak light imaging, are taken use of to meet the requirement of large dynamic range from 1 MIP to 2000 MIPs. Each crystal is coupled with two WLS fibers. As shown in Fig. 5, one fiber acting as low-range fiber which has a single-end output to the low-range ICCD. While both ends of the other fiber are led out and read out by the high-range ICCD and trigger PMTs, respectively. The ratio in amplitude between low and high range fibers is about 50 to 1, which is independent from the input energy, as shown in Fig. 6. About 12×12 pixels on the
163
Figure 4: Exploded view of the crystal array. There are five identical layers which each of them composed of 1×5×10 crystals assembly perpendicularly of the beam direction as the array. Each of the crystal is coupled with two WLS fibers for the self-trigger PMTs and ICCDs.
CCD chip are allocated to one WLS fiber. And by considering an adequate space for the nearest light spot separation, the energy deposition in the calorimeter can be derived by a 2-d image which includes 250 separate facula. The self-trigger system consisting of two PMTs is mainly dedicated to the verification of energy measurement capability of ICCDs, while it is not designed to give triggers to the ICCDs. The signal from the external trigger system goes through the calorimeter self-trigger system before being input to the ICCDs. 249 out of 250 fibers are coupled to one PMT and the fiber from the center crystal is read out by the other PMT. Fig. 7 shows the integration of all the sub systems of the calorimeter prototype. In the beam test, there are the plastic scintillator detectors (PSDs) as the external trigger system, the silicon strip detectors (SSDs) as the tracking system and the HERD calorimeter prototype along the beam line. The trigger signal from the PSDs will be broadcasted to SSDs and calorimeter. And at the same time PSDs will generate a width fixed signal which is exactly the CCD dead time, which to be coupled with the SSDs dead time feedback as the veto signal, as shown in Fig. 8 the integration and synchronization of the systems. All three systems will be synchronized by the event number provided by PSDs. About 8M events are collected during
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M. Xu / Nuclear and Particle Physics Proceedings 279–281 (2016) 161–165
Figure 5: The Upper one is the fiber winding models which build the helix shape fiber in parallel. The lower left one is the low-range fiber, which with helix shape and single-end coupled to the low-range ICCD. The lower right one is the high-range fiber, While both ends of the fiber are led out and read out by the high-range ICCD and selftrigger PMTs respectively.
Figure 6: The ratio between low and high range fibers is about 50 to 1, and independent from the input energy. The black and red point means the high range fiber is placed on the same side or perpendicular side of the crystal with the low range one, respectively. The solid and hollow point means the high range fiber is placed on the center or corner of the crystal. The ratio is smaller if the high range fiber is placed in the same side as the low range one.
Figure 7: Integration of the crystal array, self-trigger system and ICCD readout system. There are three bunches of WLS fibers derived from the array, one for the trigger PMTs which attached inside the box, and the other two bunches for the ICCDs attached outside the box as high and low range readout.
Figure 8: Integration and Synchronization of the beam test components, including the PSDs trigger system, the SSDs tracking system and the calorimeter prototype. The PSDs will provide trigger signal to the other system, and the SSDs and calorimeter will feedback veto signal to PSDs. The three system will be synchronized by event number.
M. Xu / Nuclear and Particle Physics Proceedings 279–281 (2016) 161–165
the ten days beam test and data analysis is undergoing. 5. Acknowledgments The authors would like to thank funding supports from the Chinese Strategic Pioneer Program in Space Science under Grant No.XDA04075600, the Qianren start-up grant 292012312D1117210, National Natural Science Foundation of China under Grant No.11327303 and No.11473028, and the Cross-disciplinary Collaborative Teams Program for Science, Technology and Innovation, Chinese Academy of Sciences (Research Team of The High Energy cosmic-Radiation Detection) References [1] J. R. H˝orandel, Models of the knee in the energy spectrum of cosmic rays, Astroparticle Physics 21 (3) (2004) 241 – 265. [2] G. Steigman, M. S. Turner, Cosmological constraints on the properties of weakly interacting massive particles, Nuclear Physics B 253 (0) (1985) 375 – 386. [3] J. Chang, et al., An excess of cosmic ray electrons at energies of 300 - 800GeV, Nature 456 (2008) 362–365. [4] A. A. Abdo, et al., Measurement of the Cosmic Ray e+ +e− Spectrum from 20GeV to 1TeV with the Fermi Large Area Telescope, Phys. Rev. Lett. 102 (2009) 181101. [5] O. Adriani, et al., An anomalous positron abundance in cosmic rays with energies 1.5-100 GeV, Nature 458 (2009) 607–609. [6] M. Aguilar, et al., First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5-350 GeV, Physical Review Letters 110 (14) (2013) 141102. [7] S. N. Zhang, et al., The High Energy cosmic-Radiation Detection (HERD) Facility onboard China’s Future Space Station, Proceedings of SPIE Volume 9144, 2014. [8] M. Xu, et al., Monte Carlo Simulation of HERD Calorimeter, Proceedings of SPIE Volume 9144, 2014.
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Nuclear and Particle Physics Proceedings 279–281 (2016) 161–165 www.elsevier.com/locate/nppp
The High Energy Cosmic Radiation Facility onboard China’s Space Station M. Xua , on behalf of the HERD collaboration a Key
Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China
Abstract The High Energy cosmic-Radiation Detection (HERD) facility is one of several space astronomy payloads onboard China’s Space Station, which is planned for operation starting around 2020. It is designed as a next generation space facility focused on indirect dark matter search, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey. HERD is mainly composed of a high granularity cubic calorimeter (CALO) with deep absorption length surrounded by micro-strip silicon trackers (STKs) from five sides, thus maximizing the geometrical acceptance. An overall description of the design will be described. Moreover, R&D is under way for reading out the LYSO signals with optical fiber coupled to image intensified CCD (ICCD) and the prototype of 1/40 CALO for beam test at CERN. Keywords: space experiment, calorimter, cosmic ray, beam test
1. Introduction The steepening power law of the primary cosmic ray (CR) spectrum around several PeV, the so-called knee structure is a classic problem in CR physics as it is related closely to the physics of acceleration and propagation of CRs, but still unresolved[1]. Weakly Interacting Massive Particles (WIMPs) are well motivated candidates of DM particles because they can account for the observed DM density naturally[2]. WIMPs can be detected in CRs through its annihilation into electrons or gamma-rays, resulting in structures to be seen in the otherwise predicted smooth spectra. Some circumstantial evidence or hints of anomalies have been reported[3, 4, 5, 6]; however, astrophysical sources like pulsars and pulsar wind nebulae can also contribute to these results. Experimental data from more precise measurement at higher energies are needed to address the above major problems in fundamental physics and astrophysics. The High Energy cosmic-Radiation Detection (HERD) facility has been planned as one of several space astronomy payloads of the cosmic lighthouse program onboard China’s space station, which is planned http://dx.doi.org/10.1016/j.nuclphysbps.2016.10.023 2405-6014/© 2016 Elsevier B.V. All rights reserved.
for operation starting around 2020 for about 10 years. The main scientific objectives of HERD are: 1) indirect dark matter search through spectra and anisotropy of high energy electrons and gamma-rays from 100 MeV to 10 TeV; 2) precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey from 100 MeV up to 10 TeV. In this paper, we describe the design of HERD and its basic characteristics determined with Monte-Carlo simulations, as well as ongoing R&D efforts in developing HERD prototype for beam test. 2. HERD design and expected performance Our design goal for HERD is simply to optimize its geometrical, absorption depth and its granularity, thus maximizing the acceptance after taking into account the detection and event reconstruction efficiency. To do this, we find that the HERD design with a cubic calorimeter (CALO) of 63 cm×63 cm×63 cm so as to detect particles arriving from every direction in space is required , which is made of nearly 104 pieces of granulated LYSO crystals of 3 cm×3 cm×3 cm each, as illustrated in Fig. 1. From any incident directions, CALO has a minimum
162
M. Xu / Nuclear and Particle Physics Proceedings 279–281 (2016) 161–165
Figure 2: Schematic diagram of the ICCD system. The optical taper transmits precisely the image from its input surface coupled with WLS fibers to its output surface which coupled with the image intensifier. And then the signals will be enhanced by the image intensifier and finally collected by the fast and weak light imaging CCD chip.
Please refer to Xu et al (2014) for further details of the simulations[8]. Figure 1: Schematic diagram of the baseline design of HERD. The five sides identical STKs except the bottom for mechanical support, with each side is made of seven layers of silicon micro-strips, sandwiched with tungsten foils, for absolute charge, direction and early shower measurement; the cubic CALO, for energy measurement and provide particle ID information.
stopping power of 55X0 and 3λ, where X0 and λ are radiation and nuclear interaction lengths, respectively. Such a deep and high granularity calorimeter is also essential for excellent electron-proton separation and energy resolutions of all particles. It also has some directional measurement capability with the reconstructed 3D showers. In order to measure the charges and incident directions of cosmic rays, CALO is surrounded by the same seven-layer silicon trackers (STKs) which is made of silicon micro-strip detectors sandwiched with tungsten foils from all five sides except the bottom for mechanical support, to ensure the maximum field of view (FOV) for electrons and gamma-rays. Plastic scintillators surrounding HERD from all five sides are needed to reject most low energy charged particles, in order to have maximum efficiency for high energy cosmic rays and electrons, as well as gamma-rays of all energies. Please refer to Zhang et al (2014) for more details of the requirements and design[7]. Extensive simulations have been carried out with GEANT4 and FLUKA, in order to evaluate the scientific performance of the HERD baseline design. The simulations show that electrons and photons with a high energy resolution (∼ 1% for electrons and photons and 20% for nuclei) and a large effective geometry factor (>3 m2 sr for electrons and diffuse photons and >2 m2 sr for nuclei) can be achieved under this design.
3. Beam Test Objectives The HERD calorimeter prototype is placed in the H4 beam line of the Super Proton Synchrotron (SPS) at CERN in November 2015, and data from proton, electron and fragmentation particles of primary Pb ions on a production target is collected at energies several tens of GeV up to 400 GeV. A key technology of HERD is the signal readout system of the 104 pieces of LYSO crystals with sufficient signal to noise ratio and large dynamical range. In order to minimize the power consumption of readout electronics and heat dissipation inside CALO, we choose to channel the scintillation light out of the LYSO crystals with optical coupling onto CCDs, as illustrated in Fig. 2. The beam test is intended to validate the hardware and software of HERD, and at the same time the beam test have several other major objectives including measurement of the energy resolution, angular resolution, particle identification power and data taking efficiency. As the test beams from the accelerator can only provide particle energies up to 400 GeV which is about several orders of magnitude short of HERD energy range, the response of the detector at higher energies should be carried out by using the extrapolation of Monte Carlo simulation, which means one can verify the precision of said simulations by comparing simulation to measurement at available energies and assess their likely accuracy at higher energies.
M. Xu / Nuclear and Particle Physics Proceedings 279–281 (2016) 161–165
Figure 3: Engineer drawing of the HERD beam test prototype, which including one calorimeter array composed of 250 LYSO crystals, two ICCDs as the readout system of each of the crystal at different energy range, and one self-trigger system which collect signal from all crystals through PMTs.
4. R&D of HERD Calorimeter Prototype for Beam Test The calorimeter prototype is composed of 250 LYSO crystals, two ICCDs and two self-trigger PMTs, as illustrated in Fig. 3. Each crystal with a dimension of 3×3×3 cm3 is contained in a Carbon fiber-reinforced polymer grid, as shown in Fig. 4. The space between crystals is controlled not to be larger than 0.6 mm in the horizontal/vertical direction, respectively. The 5×5×10 crystal array is designed to have the full shower shape contained of the highest SPS electrons beam, which means the main purpose of verifying the specification of electron’s energy resolution can be reached. The uniformity of light output of the crystals have been tested by using a 137 Cs radioactive source in laboratory, results shows that the variation of the crystals are within 25%. Two ICCDs, with the capability of fast and weak light imaging, are taken use of to meet the requirement of large dynamic range from 1 MIP to 2000 MIPs. Each crystal is coupled with two WLS fibers. As shown in Fig. 5, one fiber acting as low-range fiber which has a single-end output to the low-range ICCD. While both ends of the other fiber are led out and read out by the high-range ICCD and trigger PMTs, respectively. The ratio in amplitude between low and high range fibers is about 50 to 1, which is independent from the input energy, as shown in Fig. 6. About 12×12 pixels on the
163
Figure 4: Exploded view of the crystal array. There are five identical layers which each of them composed of 1×5×10 crystals assembly perpendicularly of the beam direction as the array. Each of the crystal is coupled with two WLS fibers for the self-trigger PMTs and ICCDs.
CCD chip are allocated to one WLS fiber. And by considering an adequate space for the nearest light spot separation, the energy deposition in the calorimeter can be derived by a 2-d image which includes 250 separate facula. The self-trigger system consisting of two PMTs is mainly dedicated to the verification of energy measurement capability of ICCDs, while it is not designed to give triggers to the ICCDs. The signal from the external trigger system goes through the calorimeter self-trigger system before being input to the ICCDs. 249 out of 250 fibers are coupled to one PMT and the fiber from the center crystal is read out by the other PMT. Fig. 7 shows the integration of all the sub systems of the calorimeter prototype. In the beam test, there are the plastic scintillator detectors (PSDs) as the external trigger system, the silicon strip detectors (SSDs) as the tracking system and the HERD calorimeter prototype along the beam line. The trigger signal from the PSDs will be broadcasted to SSDs and calorimeter. And at the same time PSDs will generate a width fixed signal which is exactly the CCD dead time, which to be coupled with the SSDs dead time feedback as the veto signal, as shown in Fig. 8 the integration and synchronization of the systems. All three systems will be synchronized by the event number provided by PSDs. About 8M events are collected during
164
M. Xu / Nuclear and Particle Physics Proceedings 279–281 (2016) 161–165
Figure 5: The Upper one is the fiber winding models which build the helix shape fiber in parallel. The lower left one is the low-range fiber, which with helix shape and single-end coupled to the low-range ICCD. The lower right one is the high-range fiber, While both ends of the fiber are led out and read out by the high-range ICCD and selftrigger PMTs respectively.
Figure 6: The ratio between low and high range fibers is about 50 to 1, and independent from the input energy. The black and red point means the high range fiber is placed on the same side or perpendicular side of the crystal with the low range one, respectively. The solid and hollow point means the high range fiber is placed on the center or corner of the crystal. The ratio is smaller if the high range fiber is placed in the same side as the low range one.
Figure 7: Integration of the crystal array, self-trigger system and ICCD readout system. There are three bunches of WLS fibers derived from the array, one for the trigger PMTs which attached inside the box, and the other two bunches for the ICCDs attached outside the box as high and low range readout.
Figure 8: Integration and Synchronization of the beam test components, including the PSDs trigger system, the SSDs tracking system and the calorimeter prototype. The PSDs will provide trigger signal to the other system, and the SSDs and calorimeter will feedback veto signal to PSDs. The three system will be synchronized by event number.
M. Xu / Nuclear and Particle Physics Proceedings 279–281 (2016) 161–165
the ten days beam test and data analysis is undergoing. 5. Acknowledgments The authors would like to thank funding supports from the Chinese Strategic Pioneer Program in Space Science under Grant No.XDA04075600, the Qianren start-up grant 292012312D1117210, National Natural Science Foundation of China under Grant No.11327303 and No.11473028, and the Cross-disciplinary Collaborative Teams Program for Science, Technology and Innovation, Chinese Academy of Sciences (Research Team of The High Energy cosmic-Radiation Detection) References [1] J. R. H˝orandel, Models of the knee in the energy spectrum of cosmic rays, Astroparticle Physics 21 (3) (2004) 241 – 265. [2] G. Steigman, M. S. Turner, Cosmological constraints on the properties of weakly interacting massive particles, Nuclear Physics B 253 (0) (1985) 375 – 386. [3] J. Chang, et al., An excess of cosmic ray electrons at energies of 300 - 800GeV, Nature 456 (2008) 362–365. [4] A. A. Abdo, et al., Measurement of the Cosmic Ray e+ +e− Spectrum from 20GeV to 1TeV with the Fermi Large Area Telescope, Phys. Rev. Lett. 102 (2009) 181101. [5] O. Adriani, et al., An anomalous positron abundance in cosmic rays with energies 1.5-100 GeV, Nature 458 (2009) 607–609. [6] M. Aguilar, et al., First Result from the Alpha Magnetic Spectrometer on the International Space Station: Precision Measurement of the Positron Fraction in Primary Cosmic Rays of 0.5-350 GeV, Physical Review Letters 110 (14) (2013) 141102. [7] S. N. Zhang, et al., The High Energy cosmic-Radiation Detection (HERD) Facility onboard China’s Future Space Station, Proceedings of SPIE Volume 9144, 2014. [8] M. Xu, et al., Monte Carlo Simulation of HERD Calorimeter, Proceedings of SPIE Volume 9144, 2014.
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