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803 results on '"Schunemann, P."'

151. Luminescence associated with copper in ZnGeP[sub 2].

Author

Wang, Lijun, Bai, Lihua, Stevens, K. T., Garces, N. Y., Giles, N. C., Setzler, S. D., Schunemann, P. G., and Pollak, T. M.

Subjects
ZINC crystals, LUMINESCENCE
Abstract

Bulk ZnGeP[sub 2] crystals were diffusion doped with copper and investigated using photoluminescence (PL) spectroscopy, photoluminescence excitation (PLE), and Fourier-transform-infrared spectroscopy. A PL band at 1.3 eV at 5 K was observed. The temperature dependence of the 1.3-eV PL band gives a thermal activation energy of 0.11 ± 0.01 eV. PLE data show a resonance in intensity occurred at 0.1 eV below the conduction band when monitoring the 1.3-eV band. The 1.3-eV emission band is found to be unpolarized in contrast to PL bands observed in nominally undoped ZnGeP[sub 2] crystals. The copper-diffused samples have an absorption band at 10 K peaking at about 0.62 eV. We suggest that the 1.3-eV luminescence band is donor-acceptor-pair recombination with the donor energy level about 0.1 eV below the conduction band and a Cu acceptor energy level about 0.62 eV above the valence band. This transition model is also supported by optical quenching experiments. [ABSTRACT FROM AUTHOR]

Published
2002
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152. Single-Stage Ti:sapphire-Pumped Deep-Infrared Femtosecond Optical Parametric Oscillator based on CdSiP2

Author

O’Donnell, Callum F., Chaitanya Kumar, S., Schunemann, P. G., Zawilski, K. T., Ebrahim-Zadeh, Majid, O’Donnell, Callum F., Chaitanya Kumar, S., Schunemann, P. G., Zawilski, K. T., and Ebrahim-Zadeh, Majid

Abstract

We report a high-repetition-rate femtosecond optical parametric oscillator (OPO) for the deep-infrared (deep-IR) based on the nonlinear optical crystal, CdSiP 2 (CSP), pumped directly by a Ti:sapphire laser, for the first time. By pumping CSP at <;1 μm, we have achieved practical output powers at the longest wavelengths generated by any Ti:sapphire-pumped OPO. Using a combination of pump wavelength tuning, type-I critical phase matching, and cavity delay tuning, we have generated continuously tunable radiation across 6654-8373 nm (1194-1503 cm -1 ) at 80.5-MHz repetition rate, providing up to 20 mW of average power at 7314 nm and >7 mW beyond 8000 nm, with idler spectra exhibiting bandwidths of 140-180 nm across the tuning range. Moreover, the near-IR signal is tunable across 1127-1192 nm, providing up to 37 mW of average power at 1150 nm. Signal pulses, characterized using intensity autocorrelation, have durations of ~260-320 fs, with corresponding time-bandwidth product of ΔυΔτ ~ 1. The idler and signal output exhibit a TEM00 spatial profile with single-peak Gaussian distribution. With an equivalent spectral brightness of ~6.68 × 10 20 photons s -1 mm -2 sr -1 0.1% BW -1 , this OPO represents a viable alternative to synchrotron and supercontinuum sources for deep-IR applications in spectroscopy, metrology, and medical diagnostics., Peer Reviewed, Postprint (author's final draft)

Published
2018

153. Singly-Resonant Optical Parametric Oscillator Based on Orientation-Patterned Gallium Phosphide

Author

Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, Ye, Hanyu, Chaitanya Kumar, S., Wei, Junxiong, Schunemann, P. G., Ebrahim-Zadeh, Majid, Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, Ye, Hanyu, Chaitanya Kumar, S., Wei, Junxiong, Schunemann, P. G., and Ebrahim-Zadeh, Majid

Abstract

We report a pulsed singly-resonant optical parametric oscillator based on orientation-patterned gallium phosphide pumped by a Q-switched Nd:YAG laser. The mid-IR idler can be tuned across 2.8-3.1 μm with an average power of 20 mW., Peer Reviewed, Postprint (author's final draft)

Published
2018

154. Multimilliwatt, tunable, continuous‐wave, mid‐infrared generation across 4.6‐4.7 m based on orientation‐patterned gallium phosphide

Author

Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, Devi, Kavita, Padhye, A., Schunemann, P. G., Ebrahim-Zadeh, Majid, Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, Devi, Kavita, Padhye, A., Schunemann, P. G., and Ebrahim-Zadeh, Majid

Abstract

We report the generation of tunable continuous-wave (cw) mid-infrared (mid-IR) radiation across 4608–4694 nm using the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). By exploiting difference-frequency mixing between a cw Tm-fiber laser and a home-built cw optical parametric oscillator in a 40-mm-long crystal, we have generated up to 43 mW of cw output power, with >30 mW across >95% of the mid-IR tuning range. The output at 4608 nm exhibits high beam quality with a passive power stability of 2.5% rms over 1.5 min. The temperature acceptance bandwidth of the OP-GaP crystal has been measured and compared with theory. The performance of the mid-IR source at high pump powers and polarization-dependent transmission in OP-GaP has been investigated., Peer Reviewed, Postprint (author's final draft)

Published
2018

155. Performance characterization of mid-infrared difference-frequency-generation in orientation-patterned gallium phosphide

Author

Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, Wei, JunXiong, Kumar, S. Chaitanya, Ye, Hanyu, Schunemann, P. G., Ebrahim-Zadeh, Majid, Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, Wei, JunXiong, Kumar, S. Chaitanya, Ye, Hanyu, Schunemann, P. G., and Ebrahim-Zadeh, Majid

Abstract

We present a detailed characterization of the optical properties of the recently developed nonlinear material, orientation-patterned gallium phosphide (OP-GaP), by performing difference-frequency-generation experiments in the 2548-2782 nm wavelength range in the mid-infrared (mid-IR). Temperature and spectral acceptance bandwidth measurements have been performed to study the phase-matching characteristics of OP-GaP, and the dependence of nonlinear gain on the polarization of input incident fields has been investigated. The transmission of the OP-GaP crystal at the pump and signal wavelengths has been studied and found to be dependent on polarization as well as temperature. Further, we have observed a polarization-dependent spatial shift in the transmitted pump beam through the OP-GaP sample. We have also measured the damage threshold of the OP-GaP crystal to be 0.84 J/cm2 at 1064 nm., Peer Reviewed, Postprint (published version)

Published
2018

156. Critically phase-matched Ti:sapphire-laserpumped deep-infrared femtosecond optical parametric oscillator based on CdSiP2

Author

Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, O’Donnell, Callum F., Kumar, S. Chaitanya, Zawilski, Kevin T., Schunemann, P. G., Ebrahim-Zadeh, Majid, Universitat Politècnica de Catalunya. Institut de Ciències Fotòniques, O’Donnell, Callum F., Kumar, S. Chaitanya, Zawilski, Kevin T., Schunemann, P. G., and Ebrahim-Zadeh, Majid

Abstract

We report a high-repetition-rate femtosecond optical parametric oscillator (OPO) for the deep-infrared (deep-IR) based on type-I critical phase-matching in CdSiP2 (CSP), pumped directly by a Ti:sapphire laser. Using angle-tuning in the CSP crystal, the OPO can be continuously tuned across 7306–8329 nm (1201–1369 cm−1) in the deep-IR. It delivers up to 18 mW of idler average power at 7306 nm and >7 mW beyond 8000 nm at 80.5 MHz repetition rate, with the spectra exhibiting bandwidths of >150 nm across the tuning range. Moreover, the signal is tunable across 1128–1150 nm in the near-infrared, providing up to 35 mW of average power in ∼266 fs pulses at 1150 nm. Both beams exhibit single-peak Gaussian distribution in TEM00 spatial profile. With an equivalent spectral brightness of ∼5.6×1020photons s−1 mm−2 sr−10.1% BW−1, this OPO represents a viable alternative to synchrotron and supercontinuum sources for deep-IR applications in spectroscopy, metrology, and medical diagnostics., Peer Reviewed, Postprint (author's final draft)

Published
2018

167. High-power OPCPAs at 1450–2400 nm wavelength

Author

Schunemann, Peter G., Schepler, Kenneth L., Buss, Jan Heye, Grguraš, Ivanka, Starosielec, Sebastian, Petev, Mihail, Golz, Torsten, Schulz, Michael, Prandolini, Mark, Kraus, Peter, Campi, Filippo, and Riedel, Robert

Published
2021
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181. Carrier transport and electron–lattice interactions of nonlinear optical crystals CdGeP_2, ZnGeP_2, and CdSiP_2

Author

Sooriyagoda, Rishmali, Piyathilaka, Herath P., Zawilski, Kevin T., Schunemann, Peter G., and Bristow, Alan D.

Abstract

Terahertz time-domain spectroscopy is employed to investigate temperature-dependent properties of bulk chalcopyrite crystals (CdGeP_2, ZnGeP_2, and CdSiP_2). The complex spectra provide refraction and absorption as a function of temperature, from which electron–phonon coupling and average phonon energies are extracted and linked to the mechanics of the A- and B-site cations. AC conductivity spectra provide carrier densities and electron scattering times, the temperature dependence of which are associated with unintentional shallow dopants. Temperature dependence of the scattering time is converted into carrier mobility and modeled with microscopic transport mechanisms such as polar optical phonon, acoustic phonons, deformation potential, ionized impurity, and dislocation scattering. Hence, analysis links the terahertz optical and electronic properties to relate microscopic carrier transport and carrier–lattice interactions.

Published
2021

196. Two-octave-wide (3–12??µm) subharmonic produced in a minimally dispersive optical parametric oscillator cavity

Author

Ru, Q., Kawamori, T., Schunemann, P. G., Vasilyev, S., Mirov, S. B., and Vodopyanov, K. L.

Abstract

We report a subharmonic (frequency-divide-by-2) optical parametric oscillator (OPO) with a continuous wavelength span of 3 to 12 µm (−37dB level) that covers most of the molecular rovibrational “signature” region. The key to obtaining such a wide spectral span is the use of an OPO with a minimal dispersion—through the choice of intracavity elements, the use of all gold-coated mirrors, and a special “injector” mirror. The system delivers up to 245 mW of the average power with the conversion efficiency exceeding 20% from a 2.35 µm Kerr-lens mode-locked pump laser.

Published
2021

197. Multi-millijoule, few-cycle 5??µm OPCPA at 1??kHz repetition rate

Author

von Grafenstein, Lorenz, Bock, Martin, Ueberschaer, Dennis, Escoto, Esmerando, Koç, Azize, Zawilski, Kevin, Schunemann, Peter, Griebner, Uwe, and Elsaesser, Thomas

Abstract

A table-top midwave-infrared optical parametric chirped pulse amplification (OPCPA) system generates few-cycle pulses with multi-10 GW peak power at a 1 kHz repetition rate. The all-optically synchronized system utilizes ZnGeP_2 nonlinear crystals and a highly stable 2 µm picosecond pump laser based on Ho:YLiF_4. An excellent energy extraction is achieved by reusing the pump pulse after the third parametric power amplification stage, resulting in 3.4 mJ idler pulses at a center wavelength of 4.9 µm. Pulses as short as 89.4 fs are achieved, close to only five optical cycles. Taking into account the pulse energy, a record high peak power of 33 GW for high-energy mid-IR OPCPAs beyond 4 µm wavelength is demonstrated.

Published
2020

198. DOACs vs LMWHs in hospitalized medical patients: a systematic review and meta-analysis that informed 2018 ASH guidelines

Author

Neumann, Ignacio, Izcovich, Ariel, Zhang, Yuqing, Rada, Gabriel, Kahn, Susan R., Spencer, Frederick, Rezende, Suely, Dentali, Franchesco, Bauer, Kenneth, Morgano, Gian Paolo, Yepes-Nuñez, Juan J., Nieuwlaat, Robby, Wiercioch, Wojtek, Lu, Liming, Wu, Jiaming, Cushman, Mary, and Schunemann, Holger

Abstract

Venous thromboembolism (VTE) is a relatively frequent complication in hospitalized patients, especially in those with risk factors. The benefit of using direct oral anticoagulants (DOACs) for prevention is controversial. This systematic review was performed as part of the American Society of Hematology (ASH) guidelines on VTE, developed in partnership with McMaster University. MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, and Epistemonikos were used as data sources from date of inception to November 2019. We included randomized trials in patients hospitalized for an acute medical disease, evaluating any DOACs vs other pharmacological prophylaxis, and included 3 trials with low risk of bias. We analyzed the effects of DOACs vs low-molecular-weight heparins (LMWHs) at 2 different time points: at the end of the short-term treatment phase (both drugs given for the same period of time) and at the end of the extended prophylaxis period (extended DOACs vs a shorter course of LMWHs). We observed that the use of DOACs did not reduce the risk of pulmonary embolism or symptomatic deep venous thrombosis (DVT) in comparison with LMWHs. However, the risk of major bleeding was slightly increased. Additionally, we observed that the benefit of DOACs previously reported was largely based on the reduction of asymptomatic DVT and was not apparent when only symptomatic events were considered. The use of DOACs in hospitalized medical patients slightly increases the risk of major bleeding with no appreciable benefit over LMWHs.

Published
2020
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