Browsing by Author "Liu, Jun"

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A new reaction mechanism of Claisen rearrangement induced by few-optical-cycle pulses: Demonstration of nonthermal chemistry by femtosecond vibrational spectroscopy
(2013)
Iwakura, Izumi
;
Yabushita, Atsushi
;
Liu, Jun
;
Okamura, Kotaro
;
Kezuka, Satoko
Time-resolved vibration spectroscopy is the only known way to directly observe reaction processes. In this work, we measure time-resolved vibration spectra of the Claisen rearrangement triggered and observed by few-optical-cycle pulses. Changes in molecular structure during the reaction, including its transition states (TSs), are elucidated by observing the transient changes of molecular vibration wavenumbers. We pump samples with visible ultrashort pulses of shorter duration than the molecular vibration period, and with photon energies much lower than the minimum excitation energy of the sample. The results indicate that the "nonthermal Claisen rearrangement" can be triggered by visible few-optical-cycle pulses exciting molecular vibrations in the electronic ground state of the sample, which replaces the typical thermal Claisen rearrangement.
A Novel Architecture for Autostereoscopic 2D/3D Switchable Display Using Dual Layer Strip Patterned OLED Backlight Module
(2014-05-01)
Wang, Yi-Jun
;
Liu, Jun
;
Tan, Jian
;
Yang, Bo-Ru
;
Ding, Wei-Xian
A novel backlight module that integrates dual layer strip patterned organic light emitting diode (DLSP-OLED) for 2D/3D switchable display was demonstrated. The DLSP-OLED functions as a parallax barrier in 3D mode and a planar light source in 2D mode. The results indicated that the backlight module with a thin form factor (similar to 1.1 mm) can achieve uniformity of 91% in 2D mode, and increased optical efficiency by a factor of 2.8 with a crosstalk of less than 6% in 3D mode, compared with the conventional 2D/3D switchable display. A fast switching rate (<1 ms) with simple operation can eliminate the visual fatigue caused by flicker during the switching. In addition, this configuration can function localized 3D display by modulating the DLSP-OLED individually.
Applications of parametric processes to high-quality multicolour ultrashort pulses, pulse cleaning and CEP stable sub-3fs pulse
(2012-04-14)
Kobayashi, Takayoshi
;
Liu, Jun
;
Okamura, Kotaro
;
電子物理學系
;
Department of Electrophysics
Our recent experimental results of three methods related to and useful for the generation of attosecond pulses are summarized. The pulses obtained by all of them have high qualities in terms of phase, temporal, spectral and spatial properties which are based on the physical principles associated with the parametric processes. First, carrier-envelope phase (CEP) stable sub-5 fs and sub-3 fs pulses by non-collinear optical parametric amplification (NOPA) in the near-infrared and visible spectral range will be described. The mechanism of the passive CEP stabilization is described. Passively stabilized idler and its second harmonic (SH) pulses from NOPAs are compressed to sub-5fs and sub-3fs, respectively. Compression of the idler output from a NOPA and its SH is attained with a specially designed characterization method during the compression. Second, generation of multicolour pulses by the cascaded four-wave mixing process in bulk media is discussed. As short as 15-fs multicoloured femtosecond pulses are obtained with two similar to 40 fs pulses incident to a fused-silica glass plate by this method. These broadband multicolour sidebands are expected to provide single-cycle or sub-fs pulses after the Fourier synthesis. Third, a new technique based on self-diffraction in the Kerr medium is used to clean and shorten the femtosecond laser pulse. The cleaned pulse with high temporal contrast is expected to be used as a seed for a background-free petawatt laser system and then used as the laser source for high-energy attosecond pulse generation in a solid target. The mechanisms of CEP stabilization, pulse spectral smoothening and pulse contrast enhancement are comparatively discussed.
Broadband coherent anti-Stokes Raman scattering light generation in BBO crystal by using two crossing femtosecond laser pulses
(2008-07-01)
Liu, Jun
;
Zhang, Jun
;
Kobayashi, Takayoshi
;
電子物理學系
;
Department of Electrophysics
As broad as 12000 cm(-1) coherent anti-Stokes Raman scattering (CARS) light from ultraviolet to infrared was generated in a BBO crystal by using two crossing femtosecond laser pulses with 30% conversion efficiency. More than fifteenth-order anti-Stokes and second-order Stokes Raman sidebands were observed with nice Gaussian spatial mode. The effect of the crossing angle between two input beams on the spectrum and emitting angle of the Raman sidebands was studied in detail. Calculation shows that the phase-matching condition determines the frequencies and angles of the sidebands. (C) 2008 Optical Society of America.
Cascaded four-wave mixing and multicolored arrays generation in a sapphire plate by using two crossing beams of femtosecond laser
(2008-12-22)
Liu, Jun
;
Kobayashi, Takayoshi
;
電子物理學系
;
Department of Electrophysics
Ultrabroadband signals were found to be generated by cascaded four-wave mixing in a bulk medium by using two crossing femtosecond laser pulses. As many as fifteen spectral upshifted pulses and two spectral downshifted pulses were obtained with spectral bandwidth broader than 1.5 octaves. Bright upshifted pulses were observed on both sides of the two crossing beams. Two dimensional multicolored arrays were observed for the first time in a sapphire plate medium. (c) 2008 Optical Society of America
Cascaded four-wave mixing in transparent bulk media
(2010-03-15)
Liu, Jun
;
Kobayashi, Takayoshi
;
電子物理學系
;
Department of Electrophysics
Cascaded four-wave mixing was theoretically and experimentally studied in transparent bulk media. The obtained sidebands show small angle dispersion, but have good beam quality with M(2) factor better than 1.1 in the measurement. The center wavelength of the generated multicolor sideband can be conveniently tuned by replacing the nonlinear medium with one of several different materials. Theoretical analysis and calculation based on the phase-matching condition with the consideration of broadband spectra of the two incident pulses clarified the mechanism of this process. Self-compressed multicolor 20-fs pulses, which were nearly transform-limited, were obtained when one of the two input beams was appropriately negatively chirped and the other was positively chirped. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
Clean sub-8-fs pulses at 400 nm generated by a hollow fiber compressor for ultraviolet ultrafast pump-probe spectroscopy
(2010-09-27)
Liu, Jun
;
Okamura, Kotaro
;
Kida, Yuichiro
;
Teramoto, Takahiro
;
Kobayashi, Takayoshi
Clean 7.5 fs pulses at 400 nm with less than 3% energy in tiny satellite pulses were obtained by spectral broadening in a hollow fiber and dispersive compensating using a prism pair together with a deformable mirror system. As an example, this stable and clean pulse was used to study the ultrafast pump-probe spectroscopy of photoactive yellow protein. Moreover, the self-diffraction signal shows a smoothed and broadened laser spectrum and is expected to have a further clean laser pulse, which makes it more useful in the ultrafast pump-probe spectroscopy in the future. (C) 2010 Optical Society of America
Development of real-time vibrational spectroscopy of molecules in electronic excited states: toward mapping molecular potential energy hypersurfaces
(2011-05-01)
Teramoto, Takahiro
;
Du, Juan
;
Wang, Zhuan
;
Liu, Jun
;
Tokunaga, Eiji
We have developed an experimental system for real-time vibrational spectroscopy of molecules in a specific electronic excited state. A synchronized UV light source and a few-cycle visible laser pulse were utilized to prepare and investigate the ultrafast dynamics of molecules in the electronic excited states. A multichannel lock-in amplifier detection system operating in a tandem double lock-in detection mode was used to extract the signal correlated only to the UV and visible pump pulses. Real-time vibrational spectroscopy of chrysene in the triplet state and 1', 3'-dihydro-1', 3', 3'-trimethyl-6-nitrospiro [2H-1-benzopyran-2, 2'-(2H)-indole] in a photochromic state was demonstrated. (C) 2011 Optical Society of America
Direct observation of denitrogenation process of 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH) derivatives, using a visible 5-fs pulse laser
(2012-02-27)
Abe, Manabu
;
Iwakura, Izumi
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Yabushita, Atushi
;
Yagi, Shingo
;
Liu, Jun
The mechanism of denitrogenation for 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH) derivatives was investigated using a visible 5-fs pulse laser. The time-dependent wavenumber changes observed in this study revealed that the concerted denitrogenation occurs in the parent DBH. However, a stepwise denitrogenation mechanism was found for the 7,7-diethoxy-substituted DBH derivative. (C) 2012 Elsevier B. V. All rights reserved.
Femtosecond pulses cleaning by transient-grating process Kerr-optical media
(2011-05-10)
Liu, Jun
;
Okamura, Kotaro
;
Kida, Yuichiro
;
Kobayashi, Talcayoshi
;
電子物理學系
We use a transient-grating (TG) process in a Kerr bulk medium to clean a femtosecond laser pulse. Using the technique, the temporal contrast of the generated TO signal is improved by more than two orders of magnitude in comparison with the incident pulse in a 0.5-mm-thick fused silica plate. The laser spectrum is smoothed and broadened, and the pulse duration is shortened simultaneously. We expect to extend this technique to a clean pulse with broadband spectral bandwidth at a wide spectral range because it is a phase-matched process.
Femtosecond pulses cleaning by transient-grating process Kerr-optical media
(2011-05-10)
Liu, Jun
;
Okamura, Kotaro
;
Kida, Yuichiro
;
Kobayashi, Talcayoshi
;
電子物理學系
We use a transient-grating (TG) process in a Kerr bulk medium to clean a femtosecond laser pulse. Using the technique, the temporal contrast of the generated TO signal is improved by more than two orders of magnitude in comparison with the incident pulse in a 0.5-mm-thick fused silica plate. The laser spectrum is smoothed and broadened, and the pulse duration is shortened simultaneously. We expect to extend this technique to a clean pulse with broadband spectral bandwidth at a wide spectral range because it is a phase-matched process.
Generation and Amplification of Tunable Multicolored Femtosecond Laser Pulses by Using Cascaded Four-Wave Mixing in Transparent Bulk Media
(2010-05-01)
Liu, Jun
;
Kobayashi, Takayoshi
;
電子物理學系
;
Department of Electrophysics
We have reviewed the generation and amplification of wavelength-tunable multicolored femtosecond laser pulses using cascaded four-wave mixing (CFWM) in transparent bulk media, mainly concentrating on our recent work. Theoretical analysis and calculations based on the phase-matching condition could explain well the process semi-quantitatively. The experimental studies showed: (1) as many as fifteen spectral up-shifted and two spectral down-shifted sidebands were obtained simultaneously with spectral bandwidth broader than 1.8 octaves from near ultraviolet (360 nm) to near infrared (1.2 mu m); (2) the obtained sidebands were spatially separated well and had extremely high beam quality with M(2) factor better than 1.1; (3) the wavelengths of the generated multicolor sidebands could be conveniently tuned by changing the crossing angle or simply replacing with different media; (4) as short as 15-fs negatively chirped or nearly transform limited 20-fs multicolored femtosecond pulses were obtained when one of the two input beams was negatively chirped and the other was positively chirped; (5) the pulse energy of the sideband can reach a mu J level with power stability better than 1% RMS; (6) broadband two-dimensional (2-D) multicolored arrays with more than ten periodic columns and more than ten rows were generated in a sapphire plate; (7) the obtained sidebands could be simultaneously spectra broadened and power amplified in another bulk medium by using cross-phase modulation (XPM) in conjunction with four-wave optical parametric amplification (FOPA). The characterization showed that this is interesting and the CFWM sidebands generated by this novel method have good enough qualities in terms of power stability, beam quality, and temporal features suited to various experiments such as ultrafast multicolor time-resolved spectroscopy and multicolor-excitation nonlinear microscopy.
Generation and Optimization of Femtosecond Pulses by Four-Wave Mixing Process
(2012-01-01)
Kobayashi, Takayoshi
;
Liu, Jun
;
Kida, Yuichiro
;
電子物理學系
;
Department of Electrophysics
Four-wave mixing (FWM) was used to generate and optimize ultrashort pulses with wavelengths from ultraviolet (UV) to near-infrared in bulk media and gases. Wavelength-tunable multicolored pulses were simultaneously generated by cascaded FWM in glass plates. By using incident chirped pulses, 15-fs self-compressed multicolored pulses were obtained with excellent properties. Self-compression was also used to generate ultrashort deep-UV (DUV) pulses. The positive frequency chirp in a self-phase-modulated pulseissuitable for this objective. Sub-10-fs DUV pulses were generated without using any additional pulse compressors. Self-diffraction was used to clean the pulse, broaden the spectrum, and enhance the spatial beam quality. These multicolored pulses can be simultaneously amplified and compressed by a four-wave optical parametric amplifier. The generated multicolored pulses are useful for multicolored ultrafast spectroscopy, microscopy experiments, and as seeds for petawatt lasers with high temporal contrasts.
Generation of broadband two-dimensional multicolored arrays in a sapphire plate
(2009-05-25)
Liu, Jun
;
Kobayashi, Takayoshi
;
Wang, Zhiguang
;
電子物理學系
;
Department of Electrophysics
Broadband 2-D multicolored arrays with more than ten periodic columns and more than ten rows were generated in a sapphire plate using two crossed femtosecond laser beams overlapping in time and space. These multicolored 2-D arrays were sensitive to rotation of the sapphire plate in the plane normal to the incident beams. The broadband spectrum, pulse duration less than 40fs, and less than 1%RMS power stability of the array signals make them well suited for various applications, for example multicolor pump-probe experiments. (C) 2009 Optical Society of America
Generation of mu J multicolor femtosecond laser pulses using cascaded four-wave mixing
(2009-03-30)
Liu, Jun
;
Kobayashi, Takayoshi
;
電子物理學系
;
Department of Electrophysics
Multicolor femtosecond pulses were simultaneously obtained by a cascaded FWM process in fused silica glass. The sideband spectra were tunable by changing the crossing angle of the two input beams. Frequency up-shift and down-shift pulses with energies as high as 1 mu J, durations of 45 fs, nearly diffraction limited Gaussian spatial profiles, and power stability smaller than 2% RMS of the generated sidebands were obtained. These multicolor sidebands can be used in various experiments, such as multicolor pump-probe experiment. (C) 2009 Optical Society of America
Generation of stable sub-10 fs pulses at 400 nm in a hollow fiber for UV pump-probe experiment
(2010-03-01)
Liu, Jun
;
Kida, Yuichiro
;
Teramoto, Takahiro
;
Kobayashi, Takayoshi
;
電子物理學系
Stable sub-10-fs pulses useful for many pump-probe experiments with center wavelength at 400 nm were obtained using a hollow-fiber compression technique with a beam-pointing stabilizing system. The output power stability was improved by around 2-times with the beam-pointing stabilizer. A 1-mm-thick cell sample of perylene dissolved in cyclohexane was used to test the pulse using for the pump-probe experiment. Even the high C-H stretching of vibration mode at around 2860 cm(-1), 2916 cm(-1), and 2955 cm(-1) were real-time resolved with vibrational phase information. (C) 2010 Optical Society of America
Generation of sub-20-fs multicolor laser pulses using cascaded four-wave mixing with chirped incident pulses
(2009-08-15)
Liu, Jun
;
Kobayashi, Takayoshi
;
電子物理學系
;
Department of Electrophysics
Negatively chirped or nearly transform-limited output pulses can be obtained in a four-wave mixing process when one of the pump beams is negatively chirped and the other is positively chirped. Nearly transform-limited 16 fs multicolor laser pulses are obtained in a fused-silica glass plate using this method. The resulting frequency shifts and compressed multicolor sidebands are continuously tunable in wavelength by varying the crossing angle between the two input beams. Sub-10-fs multicolor pulses should be possible obtained using this method in the future. (C) 2009 Optical Society of America
Improved efficiency of blue phosphorescence organic light-emitting diodes with irregular stepwise-doping emitting layers
(2013-03-01)
Liu, Jun
;
Wang, Jing
;
Huang, Saijun
;
Chen, Hsi-An
;
He, Gufeng
We demonstrate highly efficient blue phosphorescence organic light-emitting diodes (PHOLED) with irregular stepwise-doping emitting layers (EMLs). High efficiency is realized by inserting a high-doping EML between two relatively low-doping EMLs. Peak luminous efficiency and power efficiency of 19.2cdA1 and 18.0lmW1 are achieved, while those of a continuous stepwise-doping device are 9.8cdA1 and 8.6lmW1. The dramatic efficiency enhancement is mainly attributed to the high holeelectron recombination probability and suppressed triplet excitons quenching by fine tuning the doping concentrations in the EMLs.
Multicolor femtosecond laser with mu J level by cascaded four-wave mixing
(2010-05-01)
Kobayashi, Takayoshi
;
Liu, Jun
;
電子物理學系
;
Department of Electrophysics
Tunable multicolor femtosecond pulses were simultaneously obtained by a cascaded four-wave mixing process in a fused-silica glass plate. Frequency up-shift and down-shift pulses with energies of about 1 mu J and durations of 45 fs sidebands were obtained. When one of the two input beams was negatively chirped and the other was positively chirped, self-compressed multicolor 20 fs pulses, which were nearly transform limited, were obtained.
Photo-impulsive reactions in the electronic ground state without electronic excitation: non-photo, non-thermal chemical reactions
(2012)
Iwakura, Izumi
;
Yabushita, Atsushi
;
Liu, Jun
;
Okamura, Kotaro
;
Kobayashi, Takayoshi
Allyl phenyl ether has an absorption band in the ultraviolet region (lambda < 400 nm); therefore, irradiation with few-optical-cycle ultraviolet pulses (lambda = 360-440 nm) causes a transition to the ultraviolet band, which leads to an electronic state and a photo-Claisen rearrangement (radical reaction) in the electronic excited state. However, the reaction scheme of allyl phenyl ether under irradiation with few-optical-cycle visible pulses (lambda = 525-725 nm) was determined to be same as that of the thermal Claisen rearrangement ([3,3]-sigmatropic rearrangement), which is symmetry-allowed in the electronic ground state. Photo-excitation with few-optical cycle visible pulses below the absorption band induces a photo-impulsive reaction in the electronic ground state without electronic excitation, of which the trigger scheme is different from that of photoreaction or thermal-reaction. The photo-impulsive reaction in the electronic ground state is highly possible as a novel reaction scheme.