Browsing by Author "Lee, CK"

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Diode-pumped passively mode-locked multiwatt Nd : GdVO4 laser with a saturable Bragg reflector
(2003-09-20)
He, JL
;
Lee, CK
;
Huang, JYJ
;
Wang, SC
;
Pan, CL
We report a first demonstration, to our knowledge, of a cw passively mode-locked Nd:GdVO4 laser (lambda = 1063 nm). A relaxed saturable Bragg reflector was used. The laser generates pulses of 9.2 ps at a repetition rate of 119 MHz. As much as 5.4 W of average power was realized with a slope efficiency of 25.7%. (C) 2003 Optical Society of America.
Frequency resolved optical gating studies of strained saturable Bragg reflector: Anomalous dispersion near resonance absorption of the exciton resonance
(2005-09-01)
Lee, CK
;
Liu, TA
;
Huang, KF
;
Pan, CL
;
電子物理學系
A strained saturable Bragg reflector (SSBR) for passive mode-locking of Ti:sapphire lasers was investigated by the frequency resolved optical gating (FROG) technique. Incident pulses of several wavelengths and with zero, positive, or negative chirp were employed. A considerable pulse shortening near the excitonic resonance of the strained quantum well was observed and attributed to anomalous dispersion due to resonance absorption. On the long wavelength side of exciton resonance, however, the chirp of the reflected pulse showed a weak wavelength dependence attributed to the material dispersion of SSBR in pulse broadening was obtained.
Generation of femtosecond laser pulses tunable from 380 nm to 465 nm via cascaded nonlinear optical mixing in a noncollinear optical parametric amplifier with a type-I phase matched BBO crystal
(2003-07-14)
Lee, CK
;
Zhang, JY
;
Huang, JY
;
Pan, CL
;
光電工程學系
We report the generation of tunable femtosecond pulses from 380nm to 465nm near the degenerate point of a 405-nm pumped type-I BBO noncollinearly phase-matched optical parametric amplifier (NOPA). The tunable UV/blue radiation is obtained from sum frequency generation (SFG) between the OPA output and the residual fundamental beam at 810-nm and cascaded second harmonic generation (SHG) of OPA. With a fixed seeding angle, the generated SFG and SHG covers from 385 nm to 465-nm. With a pumping energy of 75 muJ at 405 nm, the optical conversion efficiency from the pump to the tunable SFG is more than 5% and the efficiency of SHG of the OPA is about 2%. (C) 2003 Optical Society of America.
High etching rate of GaN films by KrF excimer laser
(2001-05-22)
Chu, CF
;
Lee, CK
;
Yu, CC
;
Wang, YK
;
Tasi, JY
A study of laser processing of gallium nitride (GaN) material is reported. A pulsed KrF excimer laser at 248 nm with 20-nsec pulse width and 1 Hz repetition rate is used to etch the GaN film. We establish the material etching parameters under different environmental conditions. By changing the pulsed energy at constant pulse numbers, ablation of GaN surface was observed at threshold laser fluence about 0.3 J cm(-2). Laser etching increase with reducing environment pressure. Al 1.0 J cm (-2) laser fluence, the etching fate is about 35 nm per pulse at atmosphere pressure and increases to 60 nm per pulse at low pressure. The etched depth also increases with increasing laser fluence. The surface morphology of the etched surface was also investigated. (C) 2001 Elsevier Science B.V. All rights reserved.
Intracavity measurement of liquid crystal layer thickness by wavelength tuning of an external cavity laser diode
(2005-10-03)
Lan, YP
;
Lin, YF
;
Li, YT
;
Pan, RP
;
Lee, CK
The gap of a planar-aligned liquid crystal (LC) cell is measured by a novel method: Monitoring the change in output wavelength of an external-cavity diode laser by varying the voltage driving the LC cell placed in the laser cavity. This method is particularly suitable for measurement of LC cells of small phase retardation. Measurement errors of +/- 0.5 % and +/- 0.6 % for 9.6-mu m and 4.25-mu m cells with phase retardations of 1.63 mu m and 0.20 mu m respectively are demonstrated. (c) 2005 Optical Society of America.
Micro-photoluminescence from V-shape inverted pyramid in HVPE grown GaN film
(2002)
Lee, CK
;
Chen, YB
;
Chang, SC
;
Pan, CL
;
Wang, SC
We report the room-temperature micro-luminescence images from V-shaped inverted pyramids in undoped GaN films grown on (0001) sapphire substrate by hybrid vapor phase epitaxy. As the excitation laser spot at 325 nm was translated from the surface toward the center of the inverted pyramid along its slope, the center wavelength of the PL peak shows a trend of monotonic red-shift of from 373.9 nm to 379.1 nm. This could be attributed to the 3-dimensional release of stress and associated decrease of build-in piezoelectric field in the V-defects. A distinct and strong emission at 386.7 nm was observed at the apex of the V-defect. This could be originated from the threading dislocation at the onset of the defect.
Observation of second harmonic emission and three-photon fluorescence from Gallium-Nitride
(2000)
Lee, CK
;
Kao, FJ
;
Wang, SC
;
Pan, CL
;
光電工程學系
In this study, optical emission from the undoped GaN epilayer sample was characterized using confocal micro-spectroscopy. A femtosecond laser was used to excite the sample. As the laser wavelength tuned from 762-796nm, the sample emitted a corresponding second harmonic signal from 381-398nm with a quadratic power dependence. A strong signal at 367nm resulted from a three-photon process with cubic power dependence was simultaneously observed for the first time.
Optical properties of high density InGaN QDs grown by MOCVD
(2006-07-01)
Lee, CK
;
Hsu, JH
;
Wang, DC
;
Chang, YH
;
Kuo, HC
In this article, we investigate the relaxation time constant and optical properties of InGaN QDs following different durations of SiNx treatment. We find that the smaller size QDs have smaller red shift as temperature increasing, only about 10 meV. Time-resolved PL at various emitting wavelength of the three samples is also investigated. Decreasing time constant as increasing QDs size is observed. Besides, we also find the decreasing time constant with shorter wavelength. Meanwhile, decreasing time constant as increasing emitting wavelength is characterized and attributed as an increasing confinement of excitons in QDs with higher localization energy and thus with a higher electron-hole overlap. (c) 2005 Elsevier B.V. All rights reserved.
Population-split genetic algorithm for phase retrieval of ultrafast laser pulses
(2005)
Chen, CW
;
Shu, SF
;
Lee, CK
;
Pan, CL
;
光電工程學系
We report a new population split genetic algorithm for phase retrieval of femtosecond pulses from interferometric autocorrelation traces. After 200 GA generations, pulse width, phase, and chirp could be determined with a convergence error of 6 x 10(-3).
Simultaneous observation of second-harmonic emission and three-photon excited photoluminescence from hybrid vapor phase epitaxy-grown GaN film
(2001-12-01)
Lee, CK
;
Kao, FJ
;
Wang, SC
;
Pan, CL
;
光電工程學系
Nonlinear optical properties of the undoped hybrid vapor phase epitaxy-grown (GaTN film sample) were investigated and analyzed using a tunable femtosecond laser as an excitation source. As the laser wavelength was tuned from 762-796 nm, the sample emitted signals corresponding to the second-harmonic wavelength from 381-398 nm with a quadratic power dependence. A strong three-photon-process-related signal at 367 nm with cubic power dependence was simultaneously observed for the first time.
Sub femto-joule sensitive single-shot OPA-XFROG and its application in study of white-light supercontinuum generation
(2004-02-23)
Zhang, JY
;
Lee, CK
;
Huang, JY
;
Pan, CL
;
光電工程學系
We report a new design of single-shot cross-correlation frequency-resolved optical gating (XFROG) with sub femto-joule sensitivity for complete field characterization of ultrashort optical pulse using a 400-nm-pumped type-I noncollinear optical parametric amplifier. Optical parametric gain as high as 10(8) with 0.8-0.9 femto-joules sensitivity had been demonstrated with an un-cooled CCD in this study. The experimental FROG traces have been successfully retrieved with an error no worse than 0.0014. The device had been to be useful for studying the generation mechanism of white-light supercontinuum (WLS). (C) 2004 Optical Society of America.
Theoretical and experimental studies of tunable ultraviolet-blue femtosecond pulses in a 405-nm pumped type I beta-BaB2O4 noncollinear optical parametric amplifier and cascading sum-frequency generation
(2004-08-01)
Lee, CK
;
Zhang, JY
;
Huang, JYJ
;
Pan, CL
;
光電工程學系
Femtosecond laser pulses that are tunable from 380 to 460 nm were directly generated from a 405-nm-pumped type I beta-BaB2O4 noncollinear optical parametric amplifier (NOPA). A white-light supercontinuum from a CaF2 plate excited by 810-nm pulses was seeded into the NOPA. A theoretical analysis showed that the near-UV-to-blue radiation generated is attributable to cascaded sum-frequency generation (SFG) of the output of the NOPA and the residual fundamental beam at 810 nm. One can tune the blue-UV light by either changing the orientation of the NOPA crystal or adjusting the angle between the pump and the seeding pulse. The optical conversion efficiency from the 405-nm pump to the tunable SFG radiation is more than 5%. (C) 2004 Optical Society of America.
Time-resolved photoluminescence analysis of multidose Si-ion-implanted SiO2
(2006)
Lin, CJ
;
Lee, CK
;
Diau, EWG
;
Lin, GR
;
應用化學系
The continuous-wave/time-resolved photoluminescence (CWPL/TRPL) and capacitance - voltage (C-V) analysis of multirecipe silicon-ion-implanted SiO2 (SiO2:Si+) are demonstrated to study the lifetime evolution of three radiative defects with luminescent peaks at 415, 455, and 520 nm, which are identified as the weak oxygen bonding (O-O) defects, neutral oxygen vacancy (NOV), and precursors of nanocrystallite Si(E-delta') defects, respectively. The TRPL analysis reveals that the concentrations of weak oxygen bonding and NOV defects with lifetimes of 12 - 16 ns in as-implanted SiO2:Si+ are 3-4 x 10(17) cm(-3), agreeing well with those determined using C-V analysis. The NOV and weak oxygen-bonding defects reach their maximum densities and the shortest emission lifetimes of 7.0 x 10(18) cm(-3) and 3.6 - 7.2 ns, respectively, after annealing for 1.5 - 3 h. These results support the dissociation of SiO2 matrix during a Si-implanting process with a reaction of O-3 equivalent to Si-O-Si equivalent to O-3 -> O-3 equivalent to Si-Si equivalent to O-3 + O-interstitial -> NOV + (1/2) O-O, which is the origin of the strong blue-green CWPL observed in the SiO2:Si+. The regrowth of SiO2 matrix after long-term annealing is also confirmed by the significant reduction of NOV and weak oxygen bonding defects. In contrast, the concentration of the E-delta' center reveals a slowly increasing trend due to the less pronounced precipitation of nanocrystallite Si in SiO2:Si+ during the annealing process. (c) 2005 The Electrochemical Society.