Browsing by Author "Liu, Jia-Ming"

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Deep brain light stimulation effects on glutamate and dopamine concentration
(2015-01-01)
Kuo, Jinn-Rung
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Lin, Shih-Shian
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Liu, Janelle
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Chen, Shih-How
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Chio, Chung-Chin
Compared to deep brain electrical stimulation, which has been applied to treating pathological brain diseases, little work has been done on the effect of deep brain light stimulation. A fiber-coupled laser stimulator at 840 nm wavelength and 130 Hz pulse repetition rate is developed in this work for deep brain light stimulation in a rat model. Concentration changes in glutamate and dopamine in the striatum are observed using a microdialysis probe when the subthalamic nucleus (STN) is stimulated at various optical power levels. Experimental results show that light stimulation causes the concentration of glutamate to decrease while that of dopamine is increased. This suggests that deep brain light stimulation of the STN is a promising therapeutic strategy for dopamine-related diseases such as Parkinson's disease. The stimulator developed for this work is useful for deep brain light stimulation in biomedical research. (C) 2014 Optical Society of America
Family of graphene-assisted resonant surface optical excitations for terahertz devices
(2016-10-14)
Lin, I-Tan
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Liu, Jia-Ming
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Tsai, Hsin-Cheng
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Wu, Kaung-Hsiung
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Syu, Jheng-Yuan
The majority of the proposed graphene-based THz devices consist of a metamaterial that can optically interact with graphene. This coupled graphene-metamaterial system gives rise to a family of resonant modes such as the surface plasmon polariton (SPP) modes of graphene, the geometrically induced SPPs, also known as the spoof SPP modes, and the Fabry-Perot (FP) modes. In the literature, these modes are usually considered separately as if each could only exist in one structure. By contrast, in this paper, we show that even in a simple metamaterial structure such as a one-dimensional (1D) metallic slit grating, these modes all exist and can potentially interact with each other. A graphene SPP-based THz device is also fabricated and measured. Despite the high scattering rate, the effective SPP resonances can still be observed and show a consistent trend between the effective frequency and the grating period, as predicted by the theory. We also find that the excitation of the graphene SPP mode is most efficient in the terahertz spectral region due to the Drude conductivity of graphene in this spectral region.
Generation of an octave-spanning supercontinuum in highly nonlinear fibers pumped by noise-like pulses
(2014-01-01)
Lin, Shih-Shian
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Hwang, Sheng-Kwang
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Liu, Jia-Ming
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光電系統研究所
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Institute of Photonic System
A supercontinuum generation system is developed, which consists of an erbium-doped fiber ring laser, an erbium-doped fiber amplifier, and a 100-m highly nonlinear fiber. Through nonlinear polarization rotation, the fiber ring laser generates a train of noise-like pulses in the form of repetitive picosecond pulse packets consisting of femtosecond noise-like fine temporal structures. The noise-like pulses are amplified before being sent into the highly nonlinear fiber. As a result, an octave-spanning supercontinuum from 1177 nm to 2449 nm is obtained, which has a 20-dB spectral width of 980 nm. Because of the nonlinearity of the fiber amplifier, the duration of the noise-like pulses is shortened while their average power is enhanced. However, the enhanced pulse energy makes the key contribution to the spectral broadening of the resulting spuercontinuum in this study since the highly nonlinear fiber is so long that the effect of the pulse compression on supercontinuum generation is weak.
High-power noise-like pulse generation using a 1.56-mu m all-fiber laser system
(2015-07-13)
Lin, Shih-Shian
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Hwang, Sheng-Kwang
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Liu, Jia-Ming
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光電系統研究所
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Institute of Photonic System
We demonstrated an all-fiber, high-power noise-like pulse laser system at the 1.56-mu m wavelength. A low-power noise-like pulse train generated by a ring oscillator was amplified using a two-stage amplifier, where the performance of the second-stage amplifier determined the final output power level. The optical intensity in the second-stage amplifier was managed well to avoid not only the excessive spectral broadening induced by nonlinearities but also any damage to the device. On the other hand, the power conversion efficiency of the amplifier was optimized through proper control of its pump wavelength. The pump wavelength determines the pump absorption and therefore the power conversion efficiency of the gain fiber. Through this approach, the average power of the noise-like pulse train was amplified considerably to an output of 13.1 W, resulting in a power conversion efficiency of 36.1% and a pulse energy of 0.85 mu J. To the best of our knowledge, these amplified pulses have the highest average power and pulse energy for noise-like pulses in the 1.56-mu m wavelength region. As a result, the net gain in the cascaded amplifier reached 30 dB. With peak and pedestal widths of 168 fs and 61.3 ps, respectively, for the amplified pulses, the pedestal-to-peak intensity ratio of the autocorrelation trace remains at the value of 0.5 required for truly noise-like pulses. (C) 2015 Optical Society of America
Plasmonics in Topological Insulators
(2014-04-16)
Lai, Yi-Ping
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Lin, I-Tan
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Wu, Kuang-Hsiung
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Liu, Jia-Ming
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電子物理學系
With strong spin-orbit coupling, topological insulators have an insulating bulk state, characterized by a band gap, and a conducting surface state, characterized by a Dirac cone. Plasmons in topological insulators show high frequency-tunability in the mid-infrared and terahertz spectral regions with transverse spin oscillations, also called "spin-plasmons". This paper presents a discussion and review of the developments in this field from the fundamental theory of plasmons in bulk, thin-film, and surface-magnetized topological insulators to the techniques of plasmon excitation and future applications.
Supercontinuum generation in highly nonlinear fibers using amplified noise-like optical pulses
(2014-02-24)
Lin, Shih-Shian
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Hwang, Sheng-Kwang
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Liu, Jia-Ming
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光電系統研究所
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Institute of Photonic System
Supercontinuum generation in a highly nonlinear fiber pumped by noise-like pulses from an erbium-doped fiber ring laser is investigated. To generate ultrabroad spectra, a fiber amplifier is used to boost the power launched into the highly nonlinear fiber. After amplification, not only the average power of the noise-like pulses is enhanced but the spectrum of the pulses is also broadened due to nonlinear effects in the fiber amplifier. This leads to a reduction of the peak duration in their autocorrelation trace, suggesting a similar extent of pulse compression; by contrast, the pedestal duration increases only slightly, suggesting that the noise-like characteristic is maintained. By controlling the pump power of the fiber amplifier, the compression ratio of the noise-like pulse duration can be adjusted. Due to the pulse compression, supercontinuum generation with a broader spectrum is therefore feasible at a given average power level of the noise-like pulses launched into the highly nonlinear fiber. As a result, supercontinuum generation with an optical spectrum spanning from 1208 to 2111 nm is achieved using a 1-m nonlinear fiber pumped by amplified noise-like pulses of 15.5 MHz repetition rate at an average power of 202 mW. (C) 2014 Optical Society of America
Temperature-dependent carrier-phonon coupling in topological insulator Bi2Se3
(2014-12-08)
Lai, Yi-Ping
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Chen, Hsueh-Ju
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Wu, Kuang-Hsiung
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Liu, Jia-Ming
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電子物理學系
Temperature-dependent (11.0K +/- 294.5 K) carrier-phonon coupling in Bi2Se3 is investigated by ultrafast pump-probe spectroscopy. The rise time of the differential reflectivity is interpreted by a combined effect of electron temperature relaxation and hot-phonon lifetime. The electron-phonon coupling constant of the bulk state (lambda = 0.63 +/- 0.05) is deduced from theoretical fitting. Increasing hot-phonon lifetime with decreasing temperature is attributed to a decreasing phonon-phonon collision rate. A complete analysis of the thermalization process is presented. Understanding carrier and phonon dynamics is essential for future optoelectronic and spintronic applications of topological insulators. (C) 2014 AIP Publishing LLC.
Terahertz optical properties of multilayer graphene: Experimental observation of strong dependence on stacking arrangements and misorientation angles
(2012-12-27)
Lin, I-Tan
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Liu, Jia-Ming
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Shi, Kai-Yao
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Tseng, Pei-Shan
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Wu, Kuang-Hsiung
The optical conductivity of monolayer and multilayer graphene in the terahertz spectral region is experimentally measured using terahertz time-domain spectroscopy. The stacking arrangement and the misorientation angle of each sample are determined by Raman spectroscopy. The chemical potential of each sample is measured using ultrafast midinfrared pump-probe spectroscopy to be 63 or 64 meV for all samples. The intraband scattering rate can be obtained by fitting the measured data with theoretical models. Other physical parameters, including carrier density, dc conductivity, and carrier mobility, of each sample can also be deduced from the theoretical fitting. The fitting results show the existence of misoriented or AA-stacked layers with an interaction energy of alpha(1) = 217 meV in our multilayer samples. Here we show that the scattering rate strongly depends on the stacking arrangement of the sample. High scattering rates and high optical conductivity are associated with AA-stacked samples, while lower ones are associated with misoriented multilayer graphene. This implies that the THz optoelectronic properties of multilayer graphene can be tuned by purposefully misorienting layers or employing different stacking schemes. DOI: 10.1103/PhysRevB.86.235446 PACS number(s): 78.67.Wj, 61.48.Gh, 72.80.Vp, 73.50.Mx
Terahertz Optoelectronic Property of Graphene: Substrate-Induced Effects on Plasmonic Characteristics
(2014-03-01)
Lin, I-Tan
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Lai, Yi-Ping
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Wu, Kuang-Hsiung
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Liu, Jia-Ming
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電子物理學系
The terahertz plasmon dispersion of a multilayer system consisting of graphene on dielectric and/or plasma thin layers is systematically investigated. We show that graphene plasmons can couple with other quasiparticles such as phonons and plasmons of the substrate; the characteristics of the plasmon dispersion of graphene are dramatically modified by the presence of the coupling effect. The resultant plasmon dispersion of the multilayer system is a strong function of the physical parameters of the spacer and the substrate, signifying the importance of the substrate selection in constructing graphene-based plasmonic devices.