共查询到20条相似文献,搜索用时 30 毫秒
1.
Pouya Maraghechi Abdulhakem Y. Elezzabi 《Journal of Infrared, Millimeter and Terahertz Waves》2011,32(11):1285-1290
We present the effect of self-similarity in fractal photoconductive THz emitters. The performance of fractal THz PC emitters
are compared to those of non-fractal emitters, and their radiation properties are studied. It is demonstrated that the THz
radiation emission enhancement results from the inherent fractal self-similarity and not only from the sub-wavelength apertures
pattern present on the antenna’s surface. Through the application of this concept, photoconductive THz emitters having higher
THz radiation power could be designed and fabricated. 相似文献
2.
Shigehiko Sasa Shinya Umino Yutaro Ishibashi Toshihiko Maemoto Masataka Inoue Kei Takeya Masayoshi Tonouchi 《Journal of Infrared, Millimeter and Terahertz Waves》2011,32(5):646-654
Terahertz (THz) radiation from InAs thin films grown by molecular-beam epitaxy on closely lattice-matched p-type GaSb (100)
substrates and lattice-mismatched semi-insulating GaAs (100) substrates was investigated. The THz radiation intensity was
measured from InAs films with thicknesses between 100 nm and 1.5 μm excited by a femtosecond laser pulse with a wavelength
of approximately 780 nm. The radiation intensity increased as the InAs film thickness increased and it exceeded that from
a bulk n-type InAs substrate with an electron concentration of 2.3 × 1016 cm−3 when the InAs film thickness was greater than about 500 nm. In addition, the THz intensity from a 1-μm-thick InAs film was
greater than that from a bulk p-type InAs substrate. We ascribe this enhanced THz intensity to the wave reflected from the
lower interface between the InAs film and the layer grown beneath it. We confirmed this by observing an increased pulse width
due to constructive overlap of the reflected wave. The results demonstrate that InAs thin films are promising materials for
THz emitting devices. 相似文献
3.
Sang-Gyu Park Weiner A.M. Melloch M.R. Sider C.W. Sider J.L. Taylor A.J. 《Quantum Electronics, IEEE Journal of》1999,35(8):1257-1268
Large-aperture biased photoconductive emitters which can generate high-power narrow-band terahertz (THz) radiation are developed. These emitters avoid saturation at high fluence excitation and achieve enhanced peak power spectral density by employing a thick layer of short-lifetime low-temperature-grown GaAs (LT-GaAs) photoconductor and multiple-pulse excitation. THz waveforms are calculated from the saturation theory of large aperture photoconductors, and a comparison is made between theory and measurement. A direct comparison of the multiple-pulse saturation properties of THz emission from semi-insulating GaAs and LT GaAs emitters reveals a strong dependence on the carrier lifetime. In particular, the data demonstrate that saturation is avoided only when the interpulse spacing is longer than the carrier lifetime 相似文献
4.
Charles R. Jones Jo Dutta Guofen Yu Yuanci Gao 《Journal of Infrared, Millimeter and Terahertz Waves》2011,32(6):838-847
We describe here a system for accurate measurement of the dielectric properties of very low-loss materials in the 130 to 170 GHz
frequency range. This system utilizes an open resonator with a quality factor ∼ 1 × 106. Resonance curves for this resonator are acquired with a commercial spectrum analyzer equipped with an external millimeter-wave
harmonic mixer. The excitation source is a backward-wave oscillator locked to the spectrum analyzer local oscillator via a
digital phase-locked loop. This system permits rapid and accurate measurement of resonance curve line widths, permitting determination
of loss tangents down to the 10-6 range. Results are reported for silicon carbide (SiC), CVD diamond, sapphire, and quartz. 相似文献
5.
Terahertz (THz) waveform measurements by photoconductive (PC) sampling and free-space electrooptic sampling (FS-EOS) are analyzed and quantitatively compared. Our data suggest that a short dipole antenna used in a PC receiver contributes a flat frequency response when used without a substrate lens and a jω response when used with a substrate lens, for the specific THz frequency range and optical system investigated in our experiments. These findings are explained using results from basic antenna theory. Experiments testing our theory for a variety of THz waveforms (obtained by using different THz emitters and simple as well as shaped optical excitation pulses) and for different carrier lifetimes are also presented. Finally, we demonstrate near-field effects in the PC sampling measurements of broad-band THz waveforms and explore the evolution of THz radiation from the near field into the far field 相似文献
6.
Srinivasa Ragam Tadao Tanabe Yutaka Oyama Kenta Watanabe Hikari Dezaki 《Journal of Infrared, Millimeter and Terahertz Waves》2010,31(10):1164-1170
We constructed two types of terahertz (THz) spectrometers with automatic scanning control based on the difference frequency
generation method by the excitation of the phonon-polariton mode in GaP. The pulsed THz wave spectroscopic systems were based
on an optical parametric oscillator and Nd: YAG laser sources having a frequency resolution of 1.5 GHz, and on Cr:fosterite
sources with a resolution of 20 GHz. Following these, we recently constructed a continuous wave (CW) THz wave spectroscopic
system with laser diode excitation. One of the advantages of the CW THz wave spectrometer is its wide frequency tuning range
with fine frequency resolution of < 8 MHz. In this study, we compare both types of spectrometers (pulsed versus CW) to show
the characteristics of each system in terms of frequency resolution. The absorption spectra of a non-deformed white polyethylene
crystal and ultra-high molecular weight polyethylene with/without deformation are measured by using the CW THz wave spectrometer
and pulsed THz wave spectrometer. The effect of the high-resolution CW THz wave spectrometer is shown based on the THz spectroscopic
results. 相似文献
7.
V. N. Trukhin A. D. Bouravleuv I. A. Mustafin G. E. Cirlin D. I. Kuritsyn V. V. Rumyantsev S. V. Morosov J. P. Kakko T. Huhtio H. Lipsanen 《Semiconductors》2016,50(12):1561-1565
The paper presents the results of experimental studies of the generation of terahertz radiation in periodic arrays of GaAs nanowires via excitation by ultrashort optical pulses. It is found that the generation of THz radiation exhibits resonant behavior due to the resonant excitation of cylindrical modes in the nanowires. At the optimal geometric parameters of the nanowire array, the generation efficiency is found to be higher than that for bulk p-InAs, which is one of the most effective coherent terahertz emitters. 相似文献
8.
Yoh Matsuki Keisuke Ueda Toshitaka Idehara Ryosuke Ikeda Kosuke Kosuga Isamu Ogawa Shinji Nakamura Mitsuru Toda Takahiro Anai Toshimichi Fujiwara 《Journal of Infrared, Millimeter and Terahertz Waves》2012,33(7):745-755
In this paper we present results that demonstrate the utility of a continuously frequency-tunable 0.4 THz-gyrotron in a dynamic
nuclear polarization (DNP)-enhanced solid-state NMR (SSNMR) spectroscopy at one of the highest magnetic fields, B
0 = 14.1 T (600 MHz for 1H Larmor frequency). Our gyrotron called FU CW VI generates sub-mm wave at a frequency near 0.4 THz with an output power of
4–25 W and a tunability over a range of more than 1 GHz by sweeping the magnetic field at the gyrotron cavity. We observed
overall down shifting of the central frequency by up to ~1 GHz at high radiation duty factors and beam current, presumably
due to the cavity thermal expansion by a heating, but the tunable range was not significantly changed. The frequency tunability
facilitated the optimization of the DNP resonance condition without time-consuming field-sweep of the high-resolution NMR
magnet, and enabled us to observe substantial enhancement of the SSNMR signal (ε
DNP = 12 at 90 K). 相似文献
9.
Ugo Siciliani de Cumis Ji-Hua Xu Carlos M. Bledt James A. Harrington Alessandro Tredicucci Miriam S. Vitiello 《Journal of Infrared, Millimeter and Terahertz Waves》2012,33(3):319-326
We coupled linearly polarized and azimuthally polarized Terahertz quantum cascade lasers (QCLs) to the low-loss optical modes
of hollow core waveguides having a sequence of different metallic or dielectric inner coatings. The latter waveguides have
been specifically designed to force the propagation of a dominant optical mode once the thickness (d) of the inner dielectric
coating is properly chosen. Our results demonstrate that both the TE01 and the TE11 modes can be easily converted to a hybrid
one when d > 6 μm allowing the propagation of THz QCL beams with transmission losses as low as 1.5 dB/m, bending losses < 1.1 dB
and reasonably high coupling efficiencies (87%). 相似文献
10.
Kei Takeya Yoshiaki Takemoto Iwao Kawayama Hironaru Murakami Takeshi Matsukawa Masashi Yoshimura Yusuke Mori Masayoshi Tonouchi 《Journal of Infrared, Millimeter and Terahertz Waves》2011,32(4):426-433
We have investigated the generation of THz radiation in lithium ternary compounds LiInSe2, LiGaSe2, LiInS2, LiGaS2 and characterized these materials by THz time-domain spectroscopy. Using 800 nm femtosecond excitation pulse, all crystals
produce THz radiation due to an optical rectification corresponding to the nonlinear optical coefficient d
33. We have measured refractive indices along the x-axis and the z-axis for all crystals in the range 150–700 μm and fitted them by using Sellmeier equation. With respect to the obtained results,
velocity-matching between the incident laser pulse and the generated THz wave cannot be achieved at 800 nm, but for shorter
wavelengths. Hence, an enhanced THz generation in Lithium ternary compounds may be observed by using a laser emitting below
800 nm. 相似文献
11.
从麦克斯韦方程出发,采用电涌模型对用飞秒激光触发大间隙光导天线产生的太赫兹脉冲远场辐射特性进行研究。文章分析了大间隙GaAs光电导天线的天线电极形状和参数、天线间隙对产生的THz脉冲频谱特性的影响。用制作不同间隙、天线形状的光导天线进行产生THz辐射的实验,仿真实验结果表明:大间隙光导天线的带宽为0.1 THz~2 THz,不同的电极形状主要影响1 THz~2 THz频段内的THz信号幅值;间隙更小的光导天线的频谱带宽稍宽,而且在1 THz以上的高频段信号略高一些。 相似文献
12.
This work presents a novel scalable multiplication algorithm for a type-t Gaussian normal basis (GNB) of GF(2m). Utilizing the basic characteristics of MSD-first and LSD-first schemes with d-bit digit size, the GNB multiplication can be decomposed into n(n + 1) Hankel matrix-vector multiplications. where n = (mt + 1)/d. The proposed scalable architectures for computing GNB multiplication comprise of one d × d Hankel multiplier, four registers and one final reduction polynomial circuit. Using the relationship of the basis conversion from the GNB to the normal basis, we also present the modified scalable multiplier which requires only nk Hankel multiplications, where k = mt/2d if m is even or k = (mt − t + 2)/2d if m is odd. The developed scalable multipliers have the feature of scalability. It is shown that, as the selected digit size d ≥ 8, the proposed scalable architectures have significantly lower time-area complexity than existing digit-serial multipliers. Moreover, the proposed architectures have the features of regularity, modularity, and local interconnection ability. Accordingly, they are well suited for VLSI implementation. 相似文献
13.
小孔径蝴蝶型光电导天线太赫兹辐射源的研究 总被引:2,自引:0,他引:2
研究了5种小孔径光电导天线的太赫兹发射特性,并且对它们所发射的太赫兹波进行了对比,为研制高效率的太赫兹波发射源提供了参考依据。利用太赫兹时域光谱技术测量了光电导天线发射的太赫兹(THz)脉冲,得到了时域发射光谱,并通过快速傅里叶变换得到相应的频域光谱。结果表明,太赫兹信号强度随偏置电压的增大而增强;随着泵浦激光功率的增大而增强并出现饱和现象。偏置电压与泵浦激光功率相同时,我们对比5种光电导天线产生的太赫兹信号,从中找到了一种发射效率较高的小孔径光电导天线,并且研究了电极形状、电极间距对光电导天线发射效率的 相似文献
14.
Zhi-Xian Jiu Du-Luo Zuo Liang Miao Zu-Hai Cheng 《Journal of Infrared, Millimeter and Terahertz Waves》2010,31(12):1422-1426
Experimental studies on an efficient high-energy pulsed NH3 terahertz (THz) laser pumped by a TEA CO2 laser are presented. Pulsed THz radiation of 204 mJ with a wavelength of 151.5 μm was generated from an ammonia laser pumped
by a 32 J TEA CO2 laser tuned to the 10P(32) transition, and the photon conversion efficiency of 18% was achieved, in which the pulsed energy
was measured by pyroelectric detectors. Meanwhile, the THz transmittance was measured and compared for 5 kinds of materials.
Finally, regarding the THz transmittance of these materials, a phenomenon for ammonia radiations with 91 μm and 152 μm pumped
by a 9R(14) line was observed: i.e. while the 152 μm THz radiation can win in competition for gain at lower pressure, the
91 μm THz radiation in contrast can prevail at higher pressure. 相似文献
15.
Masahiko Tani Kohji Yamamoto Elmer S. Estacio Christopher T. Que Hidekazu Nakajima Masakazu Hibi Fumiaki Miyamaru Seizi Nishizawa Masanori Hangyo 《Journal of Infrared, Millimeter and Terahertz Waves》2012,33(4):393-404
Recent studies on the techniques and development of photoconductive (PC) semiconductor devices for efficient generation and
detection of terahertz (THz) pulsed radiation are reported. Firstly, the optimization of PC antenna design is discussed. The
PC detection of THz pulsed radiation using low-temperature grown GaAs with 1.55-μm wavelength probe is then described. Finally,
the enhancement of THz radiation from InSb by using a coupling lens and magnetic field is investigated. These results reveal
valuable insights on the design of an efficient, compact, and cost-effective THz time-domain spectroscopy system based on
1.55-μm fs laser sources. 相似文献
16.
Kaiqun Wang Chenyang Xue Ting Liang Binbin Jiao Wendong Zhang Dapeng Chen Jijun Xiong 《Journal of Infrared, Millimeter and Terahertz Waves》2010,31(7):810-820
In this paper, the design, fabrication and experimental results of the thermopile infrared detector, with a single layer of
low-stress SiNx membrane, instead of thin sandwich layer membrane of SiO2–Si3N4 are presented. Thermal isolation is achieved by using back etching of bulk silicon. Thermopiles are consisted of serially
interconnected p-poly-Si/Al thermocouples supported by the single layer of SiNx membrane with low stress. Au/Ti reflective coating was evaporated on the surface of cold junctions of the thermopile to block
incident radiation. In the measurement, we find that infrared absorbance of SiNx membrane to different wavelength is diverse and less than 100%, which has great influence on calculating the actual absorbing
power of the detector, so the infrared (IR) transmission spectrum is measured to calibrate the actual infrared absorbing amount
of the detector. The analysis result shows that only 43.72% infrared radiation is absorbed by the detector. Based on the measurement
of IR transmission spectrum and output voltage of the detector, the response sensitivity of the detector is calculated as
31.65 V/W, detectivity of the detector is 1.16 × 108 cmHz(1/2)W−1, and response time of the detector is 126 ms. 相似文献
17.
S. C. Corzo-Garcia M. Alfaro E. Castro-Camus 《Journal of Infrared, Millimeter and Terahertz Waves》2014,35(12):987-992
Monte-Carlo simulations are used to show that the transit time in ~100 nm gap photoconductive emitters of terahertz radiation is short enough to produce broad-bandwidth pulses. Furthermore, with these calculations we demonstrate that nanostructured contacts remove the need for low-temperature-grown or ion-implanted materials for broad-band terahertz devices. 相似文献
18.
S. Dvoretsky N. Mikhailov Yu. Sidorov V. Shvets S. Danilov B. Wittman S. Ganichev 《Journal of Electronic Materials》2010,39(7):918-923
We zone-engineered HgCdTe/HgTe/HgCdTe quantum wells (QWs) using the molecular-beam epitaxy (MBE) method with in situ high-precision ellipsometric control of composition and thickness. The variations of ellipsometric parameters in the ψ–Δ
plane were represented by smooth broken curves during HgTe QW growth with abrupt composition changes. The form of the spiral
fragments and their extensions from fracture to fracture revealed the growing layer composition and its thickness. Single
and multiple (up to 30) Cd
x
Hg1−x
Te/HgTe/Cd
x
Hg1−x
Te QWs with abrupt changes of composition were grown reproducibly on (013) GaAs substrates. HgTe thickness was in the range
of 16 nm to 22 nm, with the central portion of Cd
x
Hg1−x
Te spacers doped by In to a concentration of 1014 cm−3 to 1017 cm−3. Based on this research, high-quality (013)-grown HgTe QW structures can be used for all-electric detection of radiation
ellipticity in a wide spectral range, from far-infrared (terahertz radiation) to mid-infrared wavelengths. Detection was demonstrated
for various low-power continuous-wave (CW) lasers and high-power THz pulsed laser systems. 相似文献
19.
O. Hatem J. R. Freeman J. E. Cunningham P. J. Cannard M. J. Robertson E. H. Linfield A. G. Davies D. G. Moodie 《Journal of Infrared, Millimeter and Terahertz Waves》2016,37(5):415-425
We demonstrate efficient generation of terahertz (THz) frequency radiation by pulsed excitation, at wavelengths between 800 and 1550 nm, of photoconductive (PC) switches fabricated using Fe-doped InGaAsP wafers, grown by metal organic chemical vapor deposition (MOCVD). Compared to our previous studies of Fe-doped InGaAs wafers, Fe:InGaAsP wafers exhibited five times greater dark resistivity to give a value of 10 kΩ cm, and Fe:InGaAsP PC switches produced five times higher THz power emission. The effect of Fe-doping concentration (between 1E16 and 1.5E17 cm?3) on optical light absorption (between 800 and 1600 nm), on resistivity, and on THz emission is also discussed. 相似文献
20.
Ingrid Wilke Yujie J. Ding Tatiana V. Shubina 《Journal of Infrared, Millimeter and Terahertz Waves》2012,33(6):559-592
Indium nitride is a novel narrow band gap semiconductor. The material is a potential strong source of terahertz frequency
electromagnetic radiation with applications in time-domain terahertz spectroscopy and imaging systems. This article reviews
recent experimental research on terahertz emission from the binary compound semiconductor indium nitride excited by near-infrared
laser beams or microseconds electrical pulses. Advantages of indium nitride as terahertz radiation source material are discussed.
It is demonstrated that different mechanisms contribute to the emission of terahertz radiation from indium nitride. The emission
of up to 2.4 μW of THz radiation power is observed when InN is excited with near-infrared femtosecond laser pulses at an average
power of 1 W. 相似文献