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1.
Opt Lett ; 44(22): 5634-5637, 2019 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-31730126

RESUMO

We demonstrate high-energy terahertz generation from a large-aperture (75-mm diameter) lithium niobate wafer by using a femtosecond laser with energy up to 2 J. This scheme utilizes optical rectification in a bulk lithium niobate crystal, where most terahertz energy is emitted from a thin layer of the rear surface. Despite its simple setup, this scheme can yield 0.19 mJ of terahertz energy with laser-to-terahertz conversion efficiencies of ∼10-4, about 3 times better than ZnTe when pumped at 800 nm. The experimental setup is upscalable for multimillijoule terahertz generation with petawatt laser pumping.

2.
Sci Rep ; 9(1): 5811, 2019 Apr 09.
Artigo em Inglês | MEDLINE | ID: mdl-30967593

RESUMO

The valid strong THz absorption at 1.58 THz was probed in the organic-inorganic hybrid perovskite thin film, CH3NH3PbI3, fabricated by sequential vacuum evaporation method. In usual solution-based methods such as 2-step solution and antisolvent, we observed the relatively weak two main absorption peaks at 0.95 and 1.87 THz. The measured absorption spectrum is analyzed by density-functional theory calculations. The modes at 0.95 and 1.87 THz are assigned to the Pb-I vibrations of the inorganic components in the tetragonal phase. By contrast, the origin of the 1.58 THz absorption is due to the structural deformation of Pb-I bonding at the grain boundary incorporated with a CH3NH2 molecular defect.

3.
J Phys Condens Matter ; 31(2): 025701, 2019 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-30511648

RESUMO

The photonic bands of a one-dimensional photonic crystal containing epsilon-near-zero metamaterials are investigated both theoretically and numerically. A theoretical expression of the edge frequencies of the photonic bands derived from the dispersion relation of the photonic crystal is in excellent agreement with the edge frequencies of the photonic bands calculated using the plane wave expansion method. These results are also confirmed using the transmittance obtained from the transfer matrix method. The theoretical expression of the band edge frequencies indicates that the magnitude of the bandgap increases as the frequency increases in the lower bands and becomes saturated in the higher bands. This is because the bands become flat in the higher frequency range.

4.
Opt Express ; 26(19): 25315-25321, 2018 Sep 17.
Artigo em Inglês | MEDLINE | ID: mdl-30469634

RESUMO

We demonstrate a novel technique to achieve a highly efficient terahertz (THz) modulation based on hybrid structures of organic layers (fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) fabricated on both sides of a silicon (Si) substrate. The organic layer generating an optically induced electron (or hole) transfer is deposited on the back (or front) side of the Si substrate. The spatial charge separation improved owing to the transferred photo-excited electrons or holes at both interfaces of PCBM/Si and TIPS-pentacene/Si, enables a highly efficient THz wave modulation. The photoexcitation on the hole-transfer organic layer (TIPS-pentacene/Si) further improves the modulation efficiency, as the diffusion of electrons through the Si substrate is faster than that of photo-excited holes.

5.
Opt Express ; 26(10): 13677-13685, 2018 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-29801390

RESUMO

Optically tunable, strong polarization-dependent transmission of terahertz pulses through aligned Ag nanowires on a Si substrate is demonstrated. Terahertz pulses primarily pass through the Ag nanowires and the transmittance is weakly dependent on the angle between the direction of polarization of the terahertz pulse and the direction of nanowire alignment. However, the transmission of a terahertz pulse through optically excited materials strongly depends on the polarization direction. The extinction ratio increases as the power of the pumping laser increases. The enhanced polarization dependency is explained by the redistribution of photocarriers, which accelerates the sintering effect along the direction of alignment of the Ag nanowires. The photocarrier redistribution effect is examined by the enhancement of terahertz emission from the sample. Oblique metal nanowires on Si could be utilized for designing optically tunable terahertz polarization modulators.

6.
Opt Express ; 25(6): 6365-6371, 2017 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-28380988

RESUMO

We report on a method for realizing high refractive index metamaterials using corrugated metallic slot structures at terahertz frequencies. The effective refractive index and peak index frequency can be controlled by varying the width of the air gap in the corrugated slot arrays. The phenomenon occurs because of the secondary resonance effect due to the fundamental inductive-capacitive resonance, which generates a red-shift of the fundamental resonance determined by twice the length of the corrugated metallic slots. In addition, multiple gaps in the corrugated slots act as plasmonic hotspots which have the properties of three-dimensional subwavelength confinement due to extremely strong enhancement of the terahertz waves. The versatile characteristics of the structures may have many potential applications in designing compact optical devices incorporating various functionalities and in developing highly sensitive spectroscopic/imaging systems.

7.
Nanoscale ; 7(36): 14924-36, 2015 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-26300223

RESUMO

Topological insulators, a new quantum state of matter, have created exciting opportunities for studies in topological quantum physics and for exploring spintronics applications due to their gapless helical metallic surface states. In this study, thin films composed of alternate layers of Bi and Se (Te) ({Bi(3 Å)Te(9 Å)}n/{Bi(3 Å)Se(9 Å)}n) were fabricated by controlling the layer thickness within the atomic scale using thermal evaporation techniques. The high-purity growth of uniform Bi2Se2Te1 thin films has not yet been achieved using a thermal evaporation method. However, as a result of a self-ordering process during annealing, an as-grown amorphous film with p-type polarity could transform into single crystalline Bi2Se2Te1 with n-type polarity. Using THz-time domain spectroscopy (THz-TDS) and ultraviolet photoemission spectroscopy (UPS), we concluded that the conductivity is dominated by the Drude contribution, suggesting the presence of a quantum well state and surface states. Moreover we demonstrated that the emission of terahertz waves from the (001) surface of the single crystalline Bi2Se2Te1 thin film would be possible under the excitation of 790 nm femtosecond optical pulses, indicating the presence of a Dirac-fermion, a photo-Dember effect at the surface state and the transient current within the surface depletion region. The results reported herein provide useful information regarding a valuable deposition method that can be useful in studies of the evolution of surface state electrons in topological insulators.

8.
Opt Express ; 22(23): 28954-65, 2014 Nov 17.
Artigo em Inglês | MEDLINE | ID: mdl-25402134

RESUMO

We report that the Fano resonance of self-collimated beams can be achieved in a two-dimensional photonic crystal by introducing a Fano resonator that is composed of zigzag line defects. An asymmetric Fano line shape in a transmission spectrum is generated by the interference between radiated light beams from the resonator and self-collimated beams that directly pass through the resonator without resonance. It is shown that the Fano profile increases in sharpness as the number of zigzag line defects increases because the phase values of the radiated light beams change more rapidly when the number of defects increases. The Fano resonance of self-collimated beams could provide an efficient approach to manipulate light propagation and increase the possibility of application of self-collimated beams.


Assuntos
Fenômenos Ópticos , Fótons , Simulação por Computador , Cristalização , Eletricidade , Campos Magnéticos , Análise Espectral
9.
Opt Express ; 22(15): 18433-9, 2014 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-25089462

RESUMO

We first present a new phenomenon: the quarter-wavelength resonance of an electromagnetic field in planar plasmonic metamaterials consisting of asymmetrically coupled air-slot arrays, which is essential for a monopole resonator. The anti-nodal electric field intensity of the quarter-wavelength fundamental mode is formed by strong charge concentrations at the sharp metallic edges of the crossing position of the air-slots, and the nodal point of the electric field intensity naturally occurs at the other end of the air-slot. By tuning the structural asymmetry, the quarter-wavelength resonances were successfully split from the half-wavelength resonance, experimentally and numerically.

10.
Opt Express ; 22(4): 4050-8, 2014 Feb 24.
Artigo em Inglês | MEDLINE | ID: mdl-24663726

RESUMO

The propagation characteristics of spoof surface plasmon modes are studied in both real and reciprocal spaces. From the metallic square lattice, we obtain constant frequency contours by directly measuring electric fields in the microwave frequency regime. The anisotropy of the measured constant frequency contour supports the presence of the negative refraction and the self-collimation which are confirmed from measured electric fields. Additionally, we demonstrate the spoof surface plasmon beam splitter in which the splitting ratio of the self-collimated beam is controlled by varying the height of rods.

11.
Appl Opt ; 52(14): 3229-33, 2013 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-23669834

RESUMO

We report that self-collimated beams from a photonic crystal can be refracted to any direction in air by introducing an additional layer composed of dielectric rods at a photonic crystal surface. The refraction angle can be tuned from negative to positive value by adjusting the period of the additional layer. The refracted beam power can be also controllable by varying the radii of rods in the layer and the distance between the layer and the surface. The grating-induced omnidirectional refraction of self-collimated beams could provide an efficient way to manipulate light propagation and increase the possibility of application of self-collimated beams.

12.
Opt Express ; 20(8): 8309-16, 2012 Apr 09.
Artigo em Inglês | MEDLINE | ID: mdl-22513542

RESUMO

The resonant transmission of self-collimated beams through zigzag-box resonators is demonstrated experimentally and numerically. Numerical simulations show that the flat-wavefront and the width of the beam are well maintained after passing through zigzag-box resonators because the up and the down zigzag-sides prevent the beam from spreading out and the wavefront is perfectly reconstructed by the output zigzag-side of the resonator. Measured split resonant frequencies of two- and three-coupled zigzag-box resonators are well agreed with those predicted by a tight binding model to consider optical coupling between the nearest resonators. Slowing down the speed of self-collimated beams is also demonstrated by using a twelve-coupled zigzag-box resonator in simulations. Our work could be useful in implementing devices to manipulate self-collimated beams in time domain.

13.
Opt Express ; 20(6): 6116-23, 2012 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-22418491

RESUMO

We report experimental and finite-difference time-domain simulation studies on terahertz (THz) characteristics of band gaps by using metal grooves which are located inside the flare parallel-plate waveguide. The vertically localized standing-wave cavity mode (SWCM) between the upper waveguide surface and groove bottom, and the horizontally localized SWCM between two groove side walls (groove cavity) are observed. The E field intensity of the horizontally localized SWCM in grooves is very strongly enchanced which is three order higher than that of the input THz. The 4 band gaps except the Bragg band gap are caused by the π radian delay (out of phase) between the reflected THz field by grooves and the propagated THz field through the air gap. The measurement and simulation results agree well.


Assuntos
Metais/química , Refratometria/instrumentação , Ressonância de Plasmônio de Superfície/instrumentação , Projeto Auxiliado por Computador , Desenho de Equipamento , Análise de Falha de Equipamento , Radiação Terahertz
14.
Opt Express ; 20(2): 1385-91, 2012 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-22274483

RESUMO

We propose a novel design of photonic crystal fiber (PCF) using an elliptical air hole in the core as a defected core in order to enhance the performance of modal birefringence and to control the properties of chromatic dispersion at the same time. From the simulation results, it is shown that the proposed fiber has high birefringence up to the order of 10(-2), negative flattened chromatic dispersion in a broad range of wavelengths, and low confinement loss less than that of the single mode fiber. The outstanding advantage of the proposed PCF is that high birefringence, negative flattened dispersion, and low confinement loss can be achieved just by adding a small sized elliptical air hole in the core to the elliptical air hole PCF, especially at the same time.


Assuntos
Tecnologia de Fibra Óptica/instrumentação , Tecnologia de Fibra Óptica/métodos , Fibras Ópticas , Birrefringência , Simulação por Computador , Cristalização , Desenho de Equipamento
15.
Opt Express ; 19(21): 20199-204, 2011 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-21997030

RESUMO

We report on the three-dimensional subwavelength confinement of the electromagnetic waves at a coupled metallic slit structure beyond diffraction limit in terahertz region. Lateral confinement behavior, leading to the three-dimensional confinement, is caused by a strong funneling effect of the light which occurs at the intersection of slits with a sharp metal geometry. Tunability of the resonant frequency and the position of the light confinement is achieved by controlling the slit length and the position of the intersection of slits, respectively.


Assuntos
Técnicas Biossensoriais , Ressonância de Plasmônio de Superfície/métodos , Espectroscopia Terahertz/métodos , Radiação Eletromagnética , Desenho de Equipamento , Imagem Tridimensional , Teste de Materiais , Metais/química , Óptica e Fotônica
16.
Opt Express ; 19(16): 14852-9, 2011 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-21934846

RESUMO

We present a tunable notch filter having a wide terahertz (THz) frequency range and a low-pass filter (LPF) having a 0.78 THz cutoff frequency. Single slit and multiple slits are positioned at the center of air gaps in tapered parallel-plate waveguides (TPPWG) to obtain the notch filter and LPF, respectively. The notch filter has a dispersion-free and low-loss transverse magnetic (TM) mode. The Q factor was proved to be 138, and the resonant frequency is easily tunable by adjusting the air gaps between TPPWG. On the other hand, the cut off frequency of the LPF was determined using a Bragg stop band, which depends on slit period. The LPF has a transition width of 68 GHz at the cutoff frequency and a dynamic range of 35 dB at stop bands. In addition, the characteristics of such filters were analyzed using finite-difference time-domain (FDTD) simulations.


Assuntos
Técnicas Biossensoriais , Metais/química , Espectroscopia Terahertz/métodos , Ar , Simulação por Computador , Desenho de Equipamento , Filtração , Gases , Magnetismo , Refratometria , Fatores de Tempo
17.
Opt Express ; 18(24): 25371-8, 2010 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-21164885

RESUMO

Using a periodic array of split ring resonator holes within a terahertz range, we numerically and experimentally confirmed a zero refractive index at localized waveguide resonant frequency of aluminum film. The effective index was directly calculated from the phase difference of electromagnetic waves passing through film and air. Thickness-independent resonant frequency, as well as spatially static hole resonant modes, clearly verified a zero refractive index. For experimentation, we fabricated samples by means of a femtosecond laser machining system and employed a terahertz time domain spectroscopy system to measure transmitted terahertz pulses. Further, the effective index of refraction extracted from phases and amplitude of measured transmitted pulses confirmed a zero refraction index at resonant frequency.

18.
Opt Express ; 18(20): 21484-9, 2010 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-20941044

RESUMO

We investigated terahertz pulses from a rotating fan-out type poled lithium niobate (LiNbO(3)) pumped by femtosecond laser pulses. In particular, the rotating fan-out type poled sample produces an uncertain phase-matching wave vector perpendicular to input laser pulses. Such a wave vector allowed us to observe terahertz pulses normally unobservable from bulk or periodically poled LiNbO(3) at large rotation angles because of the terahertz wave critical angle of LiNbO(3). Further, we explained center frequency dependence on rotation angles by difference frequency generation process with the uncertain wave vector. We also discussed bandwidth dependence and terahertz pulse power regarding rotation angles.

19.
Opt Express ; 18(16): 17106-13, 2010 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-20721099

RESUMO

We propose a ring-type Fabry-Pérot filter (RFPF) based on the self-collimation effect in photonic crystals. The transmission characteristics of self-collimated beams are experimentally measured in this structure and compared with the results obtained with the simulations. Bending and splitting mechanisms of light beams by the line defects introduced into the RFPF are used to control the self-collimated beam. Antireflection structures are also employed at the input and output photonic crystal interfaces in order to minimize the coupling loss. Reflectance of the line-defect beam splitters can be controlled by adjusting the radius of defect rods. As the reflectance of the line-defect beam splitters increases, the transmission peaks become sharper and the filter provides a Q-factor as high as 1037. Proposed RFPF can be used as a sharply tuned optical filter or as a spectrum analyzer based on the self-collimation phenomena of photonic crystals. Furthermore, it is suitable for a building block of photonic integrated circuits, as it does not back reflect any of the incoming self-collimated beams owing to the antireflection structure applied.


Assuntos
Simulação por Computador , Filtração/instrumentação , Luz , Fótons , Espalhamento de Radiação , Cristalização/instrumentação , Desenho de Equipamento , Dispositivos Ópticos
20.
Opt Express ; 18(6): 5384-9, 2010 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-20389553

RESUMO

A two-dimensional photonic crystal asymmetric Mach-Zehnder filter (AMZF) based on the self-collimation effect is studied by numerical simulations and experimental measurements in microwave region. A self-collimated beam is effectively controlled by employing line-defect beam splitters and mirrors. The measured transmission spectra at the two output ports of the AMZF sinusoidally oscillate with the phase difference of pi in the self-collimation frequency range. Position of the transmission peaks and dips can be controlled by varying the size of the defect rod of perfect mirrors, and therefore this AMZF can be used as a tunable power filter.


Assuntos
Lentes , Refratometria/instrumentação , Refratometria/métodos , Desenho de Equipamento , Análise de Falha de Equipamento , Luz , Micro-Ondas , Fótons , Espalhamento de Radiação
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