Browsing by Author "Zhang, JY"

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Field-induced reorientation dynamics of a surface stabilized ferroelectric liquid crystal mixture
(2004-03-01)
Shih, WT
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Huang, JY
;
Zhang, JY
;
光電工程學系
;
Department of Photonics
Time-resolved measurements of electro-optical response and Fourier-transform infrared absorption have been employed to study the submolecular motion of a surface stabilized ferroelectric liquid crystal (SSFLC) mixture during a field-induced reorientation process. All observed submolecular groups were found to rotate in unison about the layer normal in a steady d.c. field. In a transient situation, the FLC director can respond rapidly to a pulsed driving field. However, the orientation distribution was found to spread at first and then slowly converge to the new direction of the FLC director. When the field is switched off, all the core groups relax to a steady-state direction with varying relaxation times. The results reveal that submolecular fragments of different molecular species in the FLC mixture move correlatively in a steady d.c. field and during a field-induced reorientation process.
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.
Intense picosecond infrared pulses tunable from 2.4-m to 38-m for nonlinear optics applications
(2005)
Chen, CW
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Hsu, YK
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Huang, JY
;
Chang, CS
;
Pan, CL
We report an intense picosecond infrared light source on microjoule energy level, widely tunable in the 2.4 - 38. m with pulse durations similar to 5ps by DFG in GaSe. The maximum photon conversion efficiency is greater than 43%.
Second-harmonic generation from regeneratively amplified femtosecond laser pulses in BBO and LBO crystals
(1998-01-01)
Zhang, JY
;
Huang, JY
;
Wang, H
;
Wong, KS
;
Wong, GK
The spectral and temporal characteristics and optical-conversion efficiency of similar to 150-fs laser pulses at 400 nm generated by second-harmonic generation (SHG) of a regeneratively amplified mode-locked Ti:sapphire laser were investigated both theoretically and experimentally. The theoretical investigation was done by taking into account cubic nonlinearity, pulse walk-off, group-velocity dispersion, Kerr nonlinearity, quadratic broadening, frequency chirping of the fundamental pulse, and higher-order nonlinear mixing such as backconversion and optical parametric processing. The experimental studies of the effects of crystal length and pumping intensity on the pulse duration, the spectrum, and the optical-conversion efficiency of the SHG were carried out in BBO and LBO crystals of various thicknesses and compared with the theory. It was found that in a non-transform-limited pulse, the most significant contribution to the temporal and spectral distortion of the similar to 150-fs SHG pulses is mainly due to the chirping of the fundamental beam and self-phase modulation at high pumping intensity and long crystal length. The optimum crystal length and pumping intensity for obtaining a high optical-conversion efficiency and a pure spectrum in SHG are also calculated and experimentally investigated. It was found that a transform-limited fundamental pulse is essential to obtain a high conversion efficiency and to preserve the temporal profile of the second-harmonic pulse. It is also found that for a non-transform-limited similar to 150-fs pulse, a 0.5-0.6-mm BBO crystal and a modest pumping intensity of similar to 40 GW/cm(2) are the most suitable for SHG. (C) 1998 Optical Society of America.
Second-harmonic generation from regeneratively amplified femtosecond laser pulses in BBO and LBO crystals
(1998-01-01)
Zhang, JY
;
Huang, JY
;
Wang, H
;
Wong, KS
;
Wong, GK
The spectral and temporal characteristics and optical-conversion efficiency of similar to 150-fs laser pulses at 400 nm generated by second-harmonic generation (SHG) of a regeneratively amplified mode-locked Ti:sapphire laser were investigated both theoretically and experimentally. The theoretical investigation was done by taking into account cubic nonlinearity, pulse walk-off, group-velocity dispersion, Kerr nonlinearity, quadratic broadening, frequency chirping of the fundamental pulse, and higher-order nonlinear mixing such as backconversion and optical parametric processing. The experimental studies of the effects of crystal length and pumping intensity on the pulse duration, the spectrum, and the optical-conversion efficiency of the SHG were carried out in BBO and LBO crystals of various thicknesses and compared with the theory. It was found that in a non-transform-limited pulse, the most significant contribution to the temporal and spectral distortion of the similar to 150-fs SHG pulses is mainly due to the chirping of the fundamental beam and self-phase modulation at high pumping intensity and long crystal length. The optimum crystal length and pumping intensity for obtaining a high optical-conversion efficiency and a pure spectrum in SHG are also calculated and experimentally investigated. It was found that a transform-limited fundamental pulse is essential to obtain a high conversion efficiency and to preserve the temporal profile of the second-harmonic pulse. It is also found that for a non-transform-limited similar to 150-fs pulse, a 0.5-0.6-mm BBO crystal and a modest pumping intensity of similar to 40 GW/cm(2) are the most suitable for SHG. (C) 1998 Optical Society of America.
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.