Browsing by Author "Hsu, Chih-Chang"

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Build-up of supercontinuum in heated and unheated photonic crystal fibers using a chirped femtosecond laser
(2006-09-15)
Lin, Ja-Hon
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Hsu, Chih-Chang
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Hsieh, Wen-Feng
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Lin, Kuel-Huei
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光電工程學系
The build-up of supercontinuum in a photonic crystal fiber (PCF) has been investigated experimentally as a function of pump power using chirped 100-fs pulses from a Ti:sapphire laser. As compared with the PCF at room temperature, a new blue-shifted spectral component is observed in the initial steps of supercontinuum (SC) generation when the central part of PCF is heated to 120 degrees C by a hot plate. In addition, the slope efficiency of SG is slightly improved with the slightly extension of supercontinuum spectrum in blue edge at high pump powers. The change in dispersion property as well as the effective cascading of nonlinear photonic crystal fibers for heated PCF would be the main attributions. (c) 2006 Elsevier B.V. All rights reserved.
Near-resonant high order nonlinear absorption of ZnO thin films
(2008-11-24)
Chan, Yun-Pei
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Lin, Ja-Hon
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Hsu, Chih-Chang
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Hsieh, Wen-Feng
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光電工程學系
Nonlinear optical absorption of ZnO thin film grown by the laser molecular beam epitaxy was investigated by the Z-scan method using a frequency-doubled femtosecond Ti:sapphire laser. Due to near-exciton resonance, an enormous enhancement of two photon absorption (TPA) is about 3000 cm/GW at 390 nm which is about 6.5 times larger than the previously reported at two-photon exciton resonance in near-IR regime and 710 times larger than that of ZnO bulk measured at 532 nm. Besides, the free-carrier absorption resulting from linear absorption and TPA becomes essential when the excitation approaches the exciton resonance. (C) 2008 Optical Society of America
Pulse-train modulation in a picosecond self-mode-locked laser
(2009-07-28)
Hsu, Chih-Chang
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Lin, Ja-Hon
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Hsieh, Wen-Feng
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光電工程學系
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Department of Photonics
Pulse-train modulation was observed in a picosecond self-mode-locked Ti:sapphire laser with pump-power dependence when it was operated around the degenerate cavity configuration. By increasing the optical pumping power, the envelope of the periodic amplitude modulation splits into two or three clusters with enhanced modulation depth, and the amplitude modulation eventually becomes disordered at higher pump power. The amplitude modulation may be supported by exciting two sets of non-degenerate longitudinally mode-locked supermodes due to spatially inhomogeneous gain modulation in the Ti: sapphire crystal.
Ultrafast carrier dynamics of InGaAsN and InGaAs single quantum wells
(2008-04-21)
Hsu, Chih-Chang
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Lin, Ja-Hon
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Chen, Ying-Shu
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Lin, Ying-Hsiu
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Kuo, Hao-Chung
Striking differences in differential reflectance and carrier relaxation in In(0.4)Ga(0.6)As and In(0.4)Ga(0.6)As(0.98)N(0.02) single quantum wells (SQWs) were studied using ultrafast time-resolved photoreflectance. Even with extremely thin SQW of only 60 angstrom within 3000 angstrom wide GaAs confining layers, negative and positive differential reflectance was observed for the excitation photon energy far above the bandgaps at 820 and 880 nm for both samples. Due to absorption by the GaAs confining layer, the peak differential reflectance pumped at 820 nm is an order of magnitude larger than that pumped at 880 nm; and it is larger for InGaAs SQWs than for InGaAsN SQWs. The shorter carrier lifetimes of these samples result from carrier - carrier scattering as pumped at both wavelengths. The longer carrier lifetime as pumped at 880 nm is due to hot phonon decay in InGaAs but may be due to stimulated emission in InGaAsN. The results reveal that the carrier dynamics is strongly affected by N incorporation that causes local defects in InGaAsN SQWs to reduce the carrier relaxation.