Browsing by Author "Zhang, Jun"

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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
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電子物理學系
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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.
Non-Condon vibronic coupling of coherent molecular vibration in MEH-PPV induced by a visible few-cycle pulse laser
(2009-01-26)
Kobayashi, Takayoshi
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Zhang, Jun
;
Wang, Zhuan
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電子物理學系
;
Department of Electrophysics
Vibrational real-time spectra of poly-[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH- PPV) were measured in a 5 fs pump-probe experiment simultaneously at 128 probe wavelengths with a multi-channel detection system. The spectral dependence of the coherent vibrational amplitudes obtained from the Fourier transform (FT) on the probe wavelength detected was found to be given by the sum of the ground-state absorption spectrum and its first and second derivatives. This indicates that the change of the transition probability caused by a wave packet motion can be explained as induced by both the non-Condon effect (non-Condon (NC) mechanism) and the time-dependent Franck-Condon factor (Frank-Condon (FC) mechanism). The FC mechanism can contribute to the first and second derivatives' dependence. On the other hand, the NC mechanism is dominant in the zeroth-order derivative. This result proves that the 1(1)B(u) exciton is strongly coupled with the excited (1)A(g) state, which is known to be essential in third-order optical nonlinearity. The amounts of shift of the absorption peaks and changes in the bandwidth due to the wave packet motions were determined for the four most prominent modes in the FT power spectra. The shift due to the FC mechanism was about 1.3-1.1% of the peak transition energy and the broadening of the vibronic transition due to the NC mechanism was about 8.0-7.6% of the bandwidth for the four modes. A novel ultrafast optical switch utilizing the modulation of electronic transition probability by molecular vibration through vibronic coupling and the interference of the wave packets is proposed.
Ultraviolet polarized light emitting and detecting dual-functioning device based on nonpolar n-ZnO/i-ZnO/p-AlGaN heterojunction
(2019-04-15)
Dai, Jiangnan
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Chen, Jingwen
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Li, Xiaohang
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Zhang, Jun
;
Long, Hanling
We report on the demonstration of a 386 nm light emission and detection dual-functioning device based on nonpolar a-plane n-ZnO/i-ZnO/p-Al0.1Ga0.9N heterojunction under both forward and reverse bias. The electroluminescence intensity under reverse bias is significantly stronger than that under forward bias, facilitated by carrier tunneling when the valence band of p-AlGaN aligns with the conduction band of i-ZnO under reverse bias. Also amid reverse bias, the photodetection was observed and applied in a duplex optical communication device. Optical polarization of the light emission is studied for potential polarization-sensitive device applications. The proposed device provides an important pathway for the multifunctional devices operating in a UV spectrum. (C) 2019 Optical Society of America
Vibrational and electronic relaxation in MEH-PPV using few cycle pulses
(2013-07-30)
Kobayashi, Takayoshi
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Yamashita, Munenori
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Du, Juan
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Zhang, Jun
;
Iwakura, Izumi
The electronic population decay time is determined to be about 500 fs in (poly-[2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylenevinylenel (MEH-PPV) using 5.7 fs pulses. The ultrafast electronic dephasing time and the self-trapping time of free exciton to form an exciton polaron is determined as 25 +/- 2 fs and 50 +/- 23 fs, respectively. Real-time spectrogram analysis reveals dynamic mode coupling among the high-frequency and low-frequency modes. The energy-ladder descent vibrational process is clarified using the first moment of the difference absorption spectrum. The phase relaxation time is calculated from the widths of the Fourier spectra of several strongly coupled modes. (C) 2013 Elsevier B.V. All rights reserved.
Vibrational fine structures revealed by the real-time vibrational phase and amplitude in MEH-PPV using few cycle pulses
(2008-04-01)
Zhang, Jun
;
Wang, Zhuan
;
Kobayashi, Takayoshi
;
電子物理學系
;
Department of Electrophysics
It was found that the vibronic transition peaks hidden in a featureless spectrum of induced absorption could be clearly revealed by utilizing the spectra of phases and amplitudes of the molecular vibrational modes. Some of the peaks were also found in a second derivative of a transition spectrum integrated over a delay time from 100 to 700 fs. This is because of the localization of a wave packet in a limited region along the potential multimode hypersurfaces. The transition energy of an induced absorption or an induced emission corresponds to some localized point (space) on the potential hypersurface to which the wave packets visit with some fixed phases.