共查询到20条相似文献,搜索用时 390 毫秒
1.
Yaohui Gao Chia-En Yang Yunching Chang Jimmy Yao Stuart Yin Claire Luo Paul Ruffin Christina Brantley Eugene Edwards 《Applied physics. B, Lasers and optics》2012,109(1):133-136
A technique of enhancing and broadening terahertz (THz) wave radiation from large aperture photoconductive (PC) antenna is presented in this paper. In this technique, the PC antenna is excited by both the optical and previously generated THz pulses by a laser-induced air plasma created in front of PC antenna and an enhanced and broadened THz wave signal is obtained. The theoretical and experimental investigation shows that the superposition is the main mechanism for this enhancement. The technique shown in this paper can be very useful for THz imaging and spectroscopy. 相似文献
2.
理论分析了介质镀膜空芯光纤在THz频段的传输特性,得出了该光纤的特征方程及模式分布。利用射线光学原理计算了介质膜材料为聚酰亚胺、介质膜厚度为0.05 mm的光纤的衰减常数随介质膜内直径的变化情况。得出其主模在THz频段的衰减常数小于1 dB/m,该值远小于相同内径的金属圆波导在这一频段的衰减常数。模拟计算了介质膜厚度为0.05 mm、内径为1 mm,金属膜内径为1.05 mm的介质镀膜空芯光纤在0~1 THz的S参数,模拟结果显示该光纤在THz频段有很宽的通带,且在通带内衰减常数小于0.5 dB/m,可用于THz频段电磁波远距离传输。 相似文献
3.
The interaction of a single quantum dot with a bowtie antenna is demonstrated for visible light. The antenna is generated at the apex of a Si3N4 atomic force microscopy tip by focused ion beam milling. When scanned over the quantum dot, its photoluminescence is enhanced while its excited-state lifetime is decreased. Our observations demonstrate that the relaxation channels of a single quantum emitter can be controlled by coupling to an efficiently radiating metallic nanoantenna. 相似文献
4.
Masahiko Tani Yuichi Hirota Christopher T. Que Shigehisa Tanaka Ryo Hattori Mariko Yamaguchi Seizi Nishizawa Masanori Hangyo 《International Journal of Infrared and Millimeter Waves》2006,27(4):531-546
The photoconductive (PC) antenna is a key device for the recent terahertz (THz) photonics based on laser-pumped generation
and detection of THz radiation. In this paper we report on two new types of PC antennas: the Schottky PC antenna and the multi-contacts
PC antenna. The former one is able to detect THz radiation intensity without the time-delay scan and useful for applications
where spectroscopic information is not important, such as the THz intensity imaging. The latter one is useful for the polarization
sensitive THz spectroscopy, such as the THz ellipsometry. The characteristic features of these new types of PC antennas are
studied by using a THz time-domain spectroscopy system. 相似文献
5.
A. Sagisaka H. Daido S. Nashima S. Orimo K. Ogura M. Mori A. Yogo J. Ma I. Daito A.S. Pirozhkov S.V. Bulanov T.Zh. Esirkepov K. Shimizu M. Hosoda 《Applied physics. B, Lasers and optics》2008,90(3-4):373-377
We have observed simultaneously both the fast proton generation and terahertz (THz) radiation in the laser pulse interaction
with a 5-μm thick titanium target. In order to control the proton acceleration and THz radiation, we have changed the duration
of the amplified spontaneous emission (ASE) preceding the main pulse generated by the high-intensity Ti:sapphire laser. A
fast proton beam with the maximal energy of ∼ 490 keV has been realized by reducing the duration of the ASE. Simultaneously,
an intense emission of THz radiation is observed for various ASE durations. We propose the antenna mechanism for the THz radiation,
according to which the fast electrons moving along the target surface emit the low-frequency electromagnetic wave.
PACS 52.25.Os; 52.38.Kd; 52.50.Jm 相似文献
6.
C. Fumeaux W. Herrmann F.K. Kneubühl H. Rothuizen B. Lipphardt C.O. Weiss 《Infrared Physics & Technology》1997,38(7):393-396
Difference frequencies up to 176 GHz between CO2-laser transitions at 28 THz (10.7 μm) are generated by thin-film nanometer-scale Ni---NiO---Ni diodes (MOM, MIM) with integrated bow-tie antennas and rhodium waveguides. A signal-to-noise (S/N) ratio of 47 dB was measured for a 58.7 GHz difference frequency and a 100 kHz bandwidth, while a S/N ratio of 14 dB was observed for a 176.2 GHz difference frequency and a 300 kHz bandwidth. The frequencies reported are considerably higher than those reported previously for thin-film diodes. The comparison of the mixing signals for the antenna parallel and perpendicular to the E-polarization of the infrared radiation yields a ratio of over 34 dB. These results imply the extension of millimeter-wave techniques to the infrared. 相似文献
7.
The properties of terahertz (THz) radiation pulses emitted by a metallic, large aspect ratio carbon nanotube antenna have been studied both in the THz waveforms and field distribution. The peak THz field up to 2.66 and 1.26 kV/cm are observed at the probe points. The proposed antenna is designed to operate for dual frequency applications from 2.36 to 2.58 THz and from 7.27 to 7.5 THz for less than -10 dB return loss. 相似文献
8.
9.
Isha Malhotra Prabhat Thakur Shweta Pandit Kumud Ranjan Jha G. Singh 《Optical and Quantum Electronics》2017,49(10):334
A compact planar antenna sources with on-chip fabrication and high directivity in order to achieve large depth-of-field for better image resolution is the prospective demand for THz imaging application. Therefore, the small-gap photoconductive dipole antennas have been explored to fulfil such applications demand. However, there are certain modalities for improving the photoconductive dipole antenna performance which need to identify to accomplish high THz average radiated power and improved total efficiency. The unit-cell small-gap photoconductive dipole antenna radiation power enhancement methods need to optimize the design parameters with photoconductive material selection from theoretical simulation. Further, the potential improvement of coupling efficiency of THz wave with air as well as femto-second laser incident efficiency is also important parameters to enhance the radiation power of small-gap photoconductive dipole antenna. In this paper, we have presented an analytical procedure employing explicit mathematical expression leading to the physical behaviour of small-gap photoconductive dipole antenna. The effects of biased lines on the antenna performance parameters are discussed with the help of proposed equivalent circuit model. We have explored the effect of gap-size on the THz radiated power and on total radiation efficiency from the proposed photoconductive dipole antennas. 相似文献
10.
With and without multi walled carbon nanotube (MWCNT) loaded graphene based optically transparent patch antennas are designed to resonate at 6 THz. Their radiation characteristics are analyzed in 5.66–6.43 THz band. The optically transparent graphene is deployed as the patch and ground plane of the antennas, which are separated by a 2.5 μm thick flexible polyimide substrate. By shorting the microstrip line and ground plane of the antenna with a MWCNT via, the return loss of the antenna is improved. The peak gain of 3.3dB at 6.2 THz and a gain greater than 3dB in 5.66–6.43 THz band is obtained for antenna loaded without MWCNT. Both the antennas achieved a −10dB impedance bandwidth of 12.83%. Gain, directivity and radiation efficiency of the proposed antennas are compared with conventional transparent patch antennas and graphene based non-transparent antennas. The antenna structures are simulated by using finite element method based electromagnetic simulator-Ansys HFSS. 相似文献
11.
Cherenkov terahertz radiation from Dirac semimetals surface plasmon polaritons excited by an electron beam 下载免费PDF全文
We demonstrate a physical mechanism for terahertz(THz) generation from surface plasmon polaritons(SPPs). In a structure with a bulk Dirac semimetals(BDSs) film deposited on a dielectric substrate, the energy of the asymmetric SPP mode can be significantly enhanced to cross the light line of the substrate due to the SPP-coupling between the interfaces of the film. Therefore, the SPPs can be immediately transformed into Cherenkov radiation without removing the wavevector mismatch. Additionally, the symmetric SPP mode can also be dramatically lifted to cross the substrate light line when a buffer layer with low permittivity relative to the substrate is introduced. In this case, dual-frequency THz radiation from the two SPP modes can be generated simultaneously. The radiation intensity is significantly enhanced by over two orders due to the field enhancement of the SPPs. The radiation frequency can be tuned in the THz frequency regime by adjusting the beam energy and the chemical potential of the BDSs. Our results could find potential applications in developing room temperature, tunable, coherent, and intense THz radiation sources to cover the entire THz band. 相似文献
12.
Takanari Yasui Takeshi Ohtsuka Tetsu Suzuki Shigeki Okajima Kazuya Nakayama Mitsuru Tomioka Katsuhiro Kamimura Takeo Namekata Hiroaki Minamide Hiromasa Ito 《International Journal of Infrared and Millimeter Waves》2006,27(2):199-210
A new, wide-band, high-speed and high-sensitivity THz detector has been developed. The prototype detector consists of a parabolic
cylindrical mirror, a long wire antenna and a Schottky barrier diode. Direct detection measurements have shown a stable sensitivity
of 150 ± 50 V/W for 1–2 THz without any adjustments. The long wire antenna was fixed at the focus of parabolic cylindrical
mirror then it has been realized less operation steps, easy coupling to the external THz signals and a dramatic enhancement
in the practicality of this system. The optically polished mirror and frosted surface one showed comparable sensitivities,
thus easy polishing and less cost mirror fabrication can be applied for this system. The radiation pattern showed a maximum
radiation angle of approximately 23° with its dominant main lobe, which was attributed to the wire antenna character and confirmed
good agreements with classical antenna theory. 相似文献
13.
Hirohisa Uchida Saroj R. Tripathi Koji Suizu Takayuki Shibuya Takashi Osumi Kodo Kawase 《Applied physics. B, Lasers and optics》2013,111(3):489-493
Widely tunable terahertz (THz) waves were successfully generated from 0.5 to 10 THz via difference frequency generation (DFG) in a configurationally locked polyene 2-[3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene] malononitrile (OH1) crystal. Potassium titanium oxide phosphate optical parametric oscillator pumped by nanosecond Q-switched Nd:YAG laser was used to generate two waves, which were then used to irradiate OH1 crystal. The maximum energy of the generated THz wave was about 461 pJ/pulse. We investigated the dependency of generated THz energy to the excitation pump power density and OH1 crystal thickness. In addition, we compared the THz energy generated by OH1 crystal to 4-N,N-dimethylamino-4′-N′-methyl-4-stilbazolium tosylate (DAST) crystal using DFG, and we achieved 560 times higher energy using OH1 crystal than DAST crystal at around 1.1 THz. 相似文献
14.
In this paper we review THz radiation properties, generation methods, and antenna configurations. This paper suggests some
new class of antennas that can be used at THz frequency, like optical antennas or Carbon nanotube antennas. THz technology
has become attractive due to the low energy content and nonionizing nature of the signal. This property makes them suitable
for imaging and sensing applications. But at the same time detection and generation of THz signals has been technologically
challenging. This paper presents a comparative study of the generation techniques for THz frequency signals giving emphasis
to the some new techniques like Quantum Cascade lasers which has created significant research interest. The main aim for this
study is to find out the materials suitable for fabricating THz devices and antennas, a suitable method for generation of
high power at THz frequency and an antenna that will make THz communication possible. 相似文献
15.
E. Estacio S. Takatori M. H. Pham T. Yoshioka T. Nakazato M. Cadatal-Raduban T. Shimizu N. Sarukura M. Hangyo C. T. Que M. Tani T. Edamura M. Nakajima J. V. Misa R. Jaculbia A. Somintac A. Salvador 《Applied physics. B, Lasers and optics》2011,103(4):825-829
Intense terahertz radiation was generated from femtosecond laser-irradiated InAs and GaAs layers on Si substrates. Results show that InAs/Si and GaAs/Si films can be excited in reflection and transmission geometries. The InAs/Si film exhibited weaker emission for both excitation cases but it will be more feasible as a spectroscopic THz source due to the absence of complex spectral features in its emission spectrum. The GaAs/Si emission is characterized by Fabry?CPerot oscillations but it is 90% of that of p-InAs bulk crystal emission intensity in the reflection geometry. Excitation fluence measurements showed that the InAs/Si film saturates easily due to the laser??s shallow penetration depth in InAs. 相似文献
16.
Simultaneous all-solid-state multi-wavelength lasers --- a promising pump source for generating highly coherent terahertz waves 下载免费PDF全文
A diode-end-pumped Nd:YAG dual-wavelength laser operating at 1319
and 1338 nm is demonstrated. The maximum average output power of
the quasi-continuous wave linearly polarized dual-wavelength laser
is obtained to be 2.1 W at a repetition rate of 50 kHz with an
output power instability of less than 0.38% and beam quality
factor M2 of 1.45. Using the two lines, the highly coherent and
narrow linewidth terahertz radiation of 3.23 THz can be generated
in an organic 4-N, N-dimethylamino--methyl-stilbazolium tosylate
(DAST) crystal. Meanwhile, the multi-wavelength red laser at 659.5,
664 and 669 nm is generated by frequency doubling and sum frequency
processes in a lithium triborate (LBO) crystal. The average red
laser output power is enhanced up to 1.625 W at a repetition rate
of 15 kHz with an output power instability of better than 0.53%
and beam quality factor M2 of 6.05. Using the three lines, it
is possible to generate the multi-wavelength THz radiation of 3.3,
3.43 and 6.73 THz in an appropriate difference frequency crystal. 相似文献
17.
《Superlattices and Microstructures》1999,25(1-2):57-60
We report on a GaAs/AlAs, wide-miniband, superlattice autocorrelator for picosecond THz radiation pulses (operated at room temperature); the autocorrelator is based on the THz radiation-induced reduction of current through the superlattice. THz radiation (frequency 7.2 THz) from the FELIX (free-electron laser for infrared experiments) was coupled into the superlattice with an antenna system. We measured the current reduction for two time-delayed pulses and found that the signal decreased when the time delay was smaller than the pulse duration. With this superlattice autocorrelator we were able to resolve laser pulses that had a duration of a few picoseconds. 相似文献
18.
This paper investigates the electromagnetic radiation
characteristics of a metallic, large aspect ratio single walled
carbon nanotube antenna in the terahertz frequency region below 12.5
THz. The key features of terahertz pulse have been revealed on the
carbon nanotube antenna in comparison with conventional
photoconductive switching. The terahertz waveforms, radiation power
and their field distributions have been evaluated and are analysed.
The Fourier transformed spectra over the whole frequency range
demonstrate that the carbon nanotube antenna can be used as
radiation source for broadband terahertz applications. 相似文献
19.
G. Singh 《Infrared Physics & Technology》2010,53(1):17-22
The effects of 2-D electromagnetic crystal substrate on the performance of a rectangular microstrip patch antennas at THz frequencies is simulated. Electromagnetic crystal substrate is used to obtain extremely broad-bandwidth with multi-frequency band operation of the proposed microstrip antennas. Multi-frequency band microstrip patch antennas are used in modern communication systems in order to enhance their capacity through frequency reuse. The simulated 10 dB impedance bandwidth of the rectangular patch microstrip antenna is 34.3% at THz frequency (0.6–0.95 THz). The radiation efficiency, gain and directivity of the proposed antenna are presented at different THz frequencies. The simulation has been performed using CST Microwave Studio, which is a commercially available electromagnetic simulator based on finite integral technique. 相似文献
20.
Guan Sun Ruolin Chen Yujie J. Ding Hieu P. T. Nguyen Zetian Mi 《Laser \u0026amp; Photonics Reviews》2015,9(1):105-113
The terahertz (THz) radiation from InGaN/GaN dot‐in‐a‐wire nanostructures has been investigated. A submicrowatt THz signal is generated with just ten vertically stacked InGaN quantum dots (QDs) in each GaN nanowire. Based on the experimental results and analysis, a single quantum wire is expected to generate an output power as high as 10 pW, corresponding to 1 pW per dot. These structures are among the most efficient three‐dimensional quantum‐confined nanostructures for the THz emission. By applying a reverse bias along the wires in a light‐emitting device (LED) consisting of such nanostructures, the THz output power is increased more than fourfold. Based on THz and photoluminescence (PL) experiments, the mechanism for the THz emission is attributed to dipole radiation induced by internal electric fields and enhanced by external fields.