Browsing by Author "Lin, Ja-Hon"

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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
;
Lin, Kuel-Huei
;
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.
Carrier dynamics of thin ZnO epifilm above band-gap states
(2009)
Ou, Po-Chi
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Lin, Ja-Hon
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Chang, C. A.
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Liu, W. R.
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Hsieh, Wen-Feng
Ultrafast carrier dynamics of ZnO epifilm were investigated by the pump probe meausrement Relative fast occruring and recovery of band gap renormalizaion following the band filling effect will result in transmission change at 362 nm.
Characteristics of a low repetition rate passively mode-locked Yb-doped fiber laser in an all-normal dispersion cavity
(2013-02-01)
Lin, Ja-Hon
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Jhu, Jia-Liang
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Jyu, Siao-Shan
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Lin, Ting-Chun
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Lai, Yinchieh
The lasing characteristics of a 365 kHz low repetition rate Yb-doped fiber laser operated in an all-normal dispersion cavity and mode-locked by the nonlinear polarization rotation mechanism are investigated in detail. As the pump power increases, the laser exhibits two transition routes when evolved from the continuous-wave (CW) state to the mode-locked (ML) state. In one evolution route the Q-switched mode-locked (QML) state is sandwiched between the CW and ML states, whereas in the other more interesting evolution route the hysteresis transition between the CW and ML states is found for the first time. Under the mode-locking operation, the laser generates sub-nanosecond pulses with linear dependence of pulsewidth on bandwidth under different pump powers, indicating the presence of giant linear chirps on the laser output pulses.
Coherent acoustic phonon oscillation accompanied with backward acoustic pulse below exciton resonance in a ZnO epifilm on oxide-buffered Si(111)
(2016-08-17)
Lin, Ja-Hon
;
Shen, Yu-Kai
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Liu, Wei-Rein
;
Lu, Chia-Hui
;
Chen, Yao-Hui
Unlike coherent acoustic phonons (CAPs) generated from heat induced thermal stress by the coated Au film, we demonstrated the oscillation from c-ZnO epitaxial film on oxide buffered Si through a degenerate pump-probe technique. As the excited photon energy was set below the exciton resonance, the electronic stress that resulted from defect resonance was used to induce acoustic wave. The damped oscillation revealed a superposition of a high frequency and long decay CAP signal with a backward propagating acoustic pulse which was generated by the absorption of the penetrated pump beam at the Si surface and selected by the ZnO layer as the acoustic resonator.
Generation of chirped long-period gratings in photonic crystal fiber using a constant period corrugated device
(2007)
Chen, Hou-Ren
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Lin, Kuei-Huei
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Lin, Ja-Hon
;
Liu, Wen-Fung
;
Hsieh, Wen-Feng
Chirped long-period fiber gratings (LPGs) are generated in bended photonic crystal fiber (PCF) by using a constant period corrugated device. As the chirping increases, the rejection bandwidth in the transmission spectra of LPGs also increases. Spectral modulation peaks are observed and the modulation depth is increased with the amount of chirping. A chirped dual LPG with rejection bandwidth of about 300 run has been obtained in a bended PCF.
Generation of supercontinuum bottle beam using an axicon
(2007-03-19)
Lin, Ja-Hon
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Wei, Ming-Dar
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Liang, Hui-Hung
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Lin, Kuei-Huei
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Hsieh, Wen-Feng
A supercontinuum bottle beam was successfully produced by focusing a supercontinuum laser beam after passing through an axicon. The supercontinuum radiation was generated from a microstructured fiber pumped by a self-kerr-lensmode-locked femtosecond Ti: sapphire laser. The cross-section intensity distributions of the generated bottle were recorded by a beam profiler. Using the line filters to select different central wavelengths, the different colors of bottle beams show slightly different bottle ranges and diameters due to the dispersion of axicon and focusing lens. The results consist with the theoretical prediction using the Fresnel-Kirchhoff's formula in considering an incident Gaussian beam. (c) 2007 Optical Society of America.
High peak power output of a diode-pumped Q-switched and mode locked Nd : LuVO4 with Cr : YAG saturable absorber
(2007)
Lin, Ja-Hon
;
Wei, Ming-Dar
;
Hsu, Hsin-Han
;
Hsieh, Wen-Feng
;
光電工程學系
The Q-switched mode-locked (QML) pulses is demonstrated in a Nd:LuVO4 laser to generate peak power exceeding 400 kW. By the Cr:YAG with initial transmittance T-0=40%, the Q-switching envelope about 30 ns and 6.9 kHz repetition rate is produced and the pulsewidth of CW-ML pulses is about 56 ps.
Multiple pulses and harmonic mode locking from passive mode-locked Ytterbium doped fiber in anomalous dispersion region
(2015-01-01)
Lin, Ja-Hon
;
Lee, Hung-Yi
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Hsieh, Wen-Feng
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光電工程學系
;
光電工程研究所
In this work, we investigate the passive mode-locked Ytterbium-doped fiber laser based on the nonlinear polarization rotation technique. With the grating pairs inside laser cavity for the GVD compensation, the total cavity dispersion is operated within anomalous dispersion region. As the laser operates at fundamental mode locking, it generates 35 MHz repetition rate mode-locked pulse with 3.3 ps pulsewidth and the optical spectrum reveals obvious Kelly side. After adjusting the waveplate or increase the pump power, the 2nd HML to 6th harmonic mode locking (HML) is demonstrated in this laser. Besides, we also generated the bound states of multiple solitons whose separation of each pulse is about several tens of picosecond. The number of solitons and the separation between sequential pulses could be controlled so that it could be used in optical communication.
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
;
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.
Pump polarization dependent ultrafast carrier dynamics and two-photon absorption in an a-plane ZnO epitaxial film
(2015-10-05)
Lin, Ja-Hon
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Su, Hsing-Jung
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Lu, Chia-Hui
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Chang, Chun-peng
;
Liu, Wei-Rein
The ultrafast carrier dynamics of non-polar a-plane ZnO epi-film, with the energy difference between the A- and C-valence bands of about 23 meV, grown on r-plane sapphire were investigated using the reflection type pump-probe technique under two perpendicular polarized pumps. By exciting the electron from A-valence band through pump pokuization perpendicular to the c-axis of a-ZnO (E-pu perpendicular to c), the TDR trace revealed two photon absorption (TPA), hand filling (BF) and bandgap renormalization (BGR) effects that can be reasonably explained by the electron dynamics in the conduction band. By exciting the electron from C-valence band through parallel pump polarization (E-pu parallel to c), only the BF effect was observed in the TDR trace owing to the hole dynamics in the valence hands. The occurrence of TPA was determined by the pump efficiency depending on the energy difference between the pump photon and the intermediate exciton resonance state. (C) 2015 AIP Publishing LLC.
Q-switched and mode locked pulses generated from c-cut Nd:LuVO4
(2009)
Song, Kun-Tai
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Lin, Ja-Hon
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Chen, Hou-Ren
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Lin, Kuei-Huei
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Hsieh, Wen-Feng
Q-switched and mode locked pulses have been demonstraed in c-cut Nd center dot LuVO4 laser Using 80% initial transmittance of Cr4+ YAG and output coupler with 70% refleactane, large pulse energy of about 112 mu J has been demonstrated at 18 W pumping.
Room temperature excitonic dynamics of non-polar a-plane ZnO epifilms
(2016-09)
Lin, Ja-Hon
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Liu, Wei-Rein
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Lin, Yi-Chin
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Su, Hsing-Jung
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Chen, Hou-Ren
Pump polarization dependent carrier dynamics, particularly excitonic dynamics, of non-polar a-plane zinc oxide (ZnO) epifilms with two different thicknesses were investigated using time resolved measurements. Unlike the electron and hole dynamics through the above-bandgap excitation, transient differential reflectance (TDR) traces revealed similar trends under two orthogonal pump polarization conditions relative to the c-axis (E-pu +/- c and E-pu vertical bar vertical bar c) of a-ZnO around near-exciton-resonance excitation. By means of a band diagram, the bandgap renormalization (BGR) effect can be reasonably explained by the screening of the Coulomb potential energy due to the accumulation of relaxed free carriers that were initially excited through the absorption of two cascaded pump photons via the excitonic level, a process known as two photon absorption (TPA). Thus, the modulation depths of the TPA around zero time delay, due to simultaneous absorption of one pump and one probe photon via the excitonic level, increased linearly with the pump fluence, proportional to the modulation depth resulting from the BGR effects. (C) 2016 Author(s).
Saturation and beating of acoustic phonon oscillations excited near the exciton resonance of strained polar ZnO/Zn0.8Mg0.2O multiple quantum wells
(2018-01-01)
Liu, Wei-Rein
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Lin, Ja-Hon
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Chen, Jyun-Sian
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Cheng, Hsin-Ming
;
Li, Sheng-Jie
Saturation and beating of coherent acoustic phonon (CAP) oscillations were observed and attributed to the screening of a built-in electric field with increasing pump power using degenerate pump-probe measurements near the exciton resonance of polar ZnO/Zn0.8Mg0.2O multiple quantum wells (MQWs). After purifying the CAP signals by using an empirical mode decomposition, we found not only that the CAP amplitude follows the trend of the band gap renormalization (BGR) and shows saturation at high pump power, but also that the CAP oscillation period coincides with that of the MQWs, consistent with the XRD and TEM results. An additional low-frequency oscillation modifying the CAP signal is revealed due to the negative change in refractive index caused by BGR as the pump power increases.
Stable Q-switched mode-locked Nd3+:LuVO4 laser by Cr4+:YAG crystal
(2008-10-13)
Lin, Ja-Hon
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Chen, Hou-Ren
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Hsu, Hsin-Han
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Wei, Ming-Dar
;
Lin, Kuei-Huei
In use of saturable Cr4+:YAG crystals, we have demonstrated the stable Q-switched and mode-locked (QML) operation of the Nd:LuVO4 laser. The operation range of QML in use of the Cr4+:YAG is larger than that use of SESAM and NLM. The obtained shape of Q-switched envelope, repetition rate and pulse energy are demonstrated to depend on the initial transmittance of the Cr4+:YAG and reflectivity of the output coupler. Using R = 60% and T-0 = 40%, the highest pulse energy of 77 mu J of each Q-switched envelope, and the highest peak power about 200 kW of Q-switched mode-locked pulses can be obtained at 15 W pump power. It demonstrate the superior characteristic of the Nd:LuVO4 crystal. (C) 2008 Optical Society of America
Stress-Induced Versatile Tunable Long-Period Gratings in Photonic Crystal Fibers
(2008-09-01)
Chen, Hou-Ren
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Lin, Kuei-Huei
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Lin, Ja-Hon
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Hsieh, Wen-Feng
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光電工程學系
We report a method for generating versatile tunable long-period gratings (LPGs) in photonic crystal fibers (PCFs). The central wavelength and rejection bandwidth of LPGs can be tuned over a broad spectral range with adjustable transmission loss. Spectral fringes with uneven spacing are observed in chirped LPGs, depending on the interaction length and the amount of chirping between the two ends of the LPG, and can be removed by reducing the chirping and increasing the grating length. By utilizing a stress-induced LPG, gain flattening of an erbium-doped fiber amplifier has also been demonstrated.
Thickness effect on ultrafast thermalization of carriers in above-band-gap states in ZnO epitaxial films
(2010-12-15)
Ou, Po-Chi
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Lin, Ja-Hon
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Chang, Chi-An
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Liu, Wei-Rein
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Hsieh, Wen-Feng
Energy-dependent free-carrier dynamics was investigated in 70 nm (thin) and 1 mu m (thick) ZnO epifilms using the optical pump-probe technique. The far-above-band-gap dynamics in the thin epifilm reveals the prolonged relaxation and the slow recovery of renormalized band gap. The band-gap renormalization (BGR) effect is affected by the inefficient carrier-phonon scattering. In addition, the loss of excited carrier density via surface trapping results in an energy-dependent BGR buildup time. However, the far-above-band-gap dynamics in the thick epifilm reveals fast relaxation followed by BGR recovery, which is independent of the photon energy. The near-band-gap dynamics shows an ultrafast carrier thermalization both in the thin and the thick epifilms.
Ultra-short Pulse Compression for Mode-locked Ti:sapphire Laser by using a Tapered Fiber
(2009-01-01)
Hsu, Kuei-Chu
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Lin, Ja-Hon
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Taso, Chih-Chieh
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Chen, Nan-Kuang
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Lai, Yinchieh
Ultra-short pulse compression for tunable mode-locked Ti:sapphire lasers is demonstrated by utilizing a 1-mu m-diameter tapered fiber with grating pairs. For 100 fs input pulses at the 880-nm center wavelength, the optical bandwidth is broaden from 14 tun to 45 ran after propagating through the 1-cm long tapered fiber. After passing through the grating pairs with 1.6 cm separation, the final pulse width is compressed down to 33 fs. (C) 2009 Optical Society of America
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.
Ultrafast relaxation and absorption saturation at near exciton resonance in a thin ZnO epilayer
(2011-01-01)
Ou, Po-Chi
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Liu, Wei-Rein
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Ton, Ho-Jei
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Lin, Ja-Hon
;
Hsieh, Wen-Feng
We observed ultrafast free exciton thermalization time of 700-900 fs and obtained the magnitude of maximal differential absorption to be 1.8 x 10(4) cm(-1) with the pumping fluence of 10 mu J/cm(2) by measuring transient differential transmission in a thin ZnO epitaxial layer at room temperature. The largest induced transparency occurs near exciton resonance associated with absorption saturation by comparing the excitation from the above band-gap to band-tail states. The pumping dependent transient absorption reveals transition of excitonic relaxation from exciton-phonon scattering to exciton-exciton scattering or to an electron-hole plasma. (C) 2011 American Institute of Physics. [doi:10.1063/1.3525993]