Browsing by Subject "Breakdown"
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Item Open Access Air-guided photonic-crystal-fiber pulse-compression delivery of multimegawatt femtosecond laser output for nonlinear-optical imaging and neurosurgery(AIP Publishing LLC, 2012-03-06) Lanin, A.; Fedotov, I. V.; Sidorov Biryukov, D. S.; Doronina Amitonova, L. V.; Ivashkina, O. I.; Zots, M. A.; Sun, C. K.; Ilday, F. O.; Fedotov, A. B.; Anokhin, K. V.; Zheltikov, A. M.Large-core hollow photonic- crystal fibers (PCFs) are shown to enable a fiber-format air-guided delivery of ultrashort infrared laser pulses for neurosurgery and nonlinear-optical imaging. With an appropriate dispersion precompensation, an anomalously dispersive 15-mu m-core hollow PCF compresses 510-fs, 1070-nm light pulses to a pulse width of about 110 fs, providing a peak power in excess of 5 MW. The compressed PCF output is employed to induce a local photodisruption of corpus callosum tissues in mouse brain and is used to generate the third harmonic in brain tissues, which is captured by the PCF and delivered to a detector through the PCF cladding.Item Open Access Improvement of breakdown characteristics in AlGaN/GaN/AlxGa 1-xN HEMT based on a grading Al xGa 1-xN buffer layer(Wiley, 2010-08-03) Yu, H.; Lisesivdin, S. B.; Ozturk, M.; Bolukbas, B.; Kelekci, O.; Ozturk, M. K.; Ozcelik, S.; Caliskan, D.; Cakmak, H.; Demirel, P.; Özbay, EkmelTo improve the breakdown characteristics of an AlGaN/GaN based high electron mobility transistor (HEMT) for high voltage applications, AlGaN/GaN/Al xGa 1-xN double heterostructure (DH-HEMTs) were designed and fabricated by replacing the semi-insulating GaN buffer with content graded Al xGa 1-xN (x=x 1 → x 2, x 1 > x 2), in turn linearly lowering the Al content x from x 1=90% to x 2=5% toward the front side GaN channel on a high temperature AlN buffer layer. The use of a highly resistive Al xGa 1-xN epilayer suppresses the parasitic conduction in the GaN buffer, and the band edge discontinuity limits the channel electrons spillover, thereby reducing leakage current and drain current collapse. In comparison with the conventional HEMT that use a semi-insulating GaN buffer, the fabricated DH-HEMT device with the same size presents a remarkable enhancement of the breakdown voltage.