Abstract-Performance evaluation of tunneling field effect transistor on Terahertz detection

Q. Yang, J. Zhang,  C. Zhu,  X. Lin, F. Yan, X. Ji

https://ieeexplore.ieee.org/document/8369195

Tunneling field-effect transistor (TFET) with integrated circuit manufacture process is capable of rectifying high frequency radiations in THz region. As an efficient device to detect Terahertz signal. In this paper, we demonstrate a Si-based TFET device for THz imaging. The static characteristics and THz performance are presented by using technology computer-aided design simulation. For an optimally designed TFETs with SS of 40.3mV/dec, it has a high responsivity of 4300V/W to a 1THz radiation. Compared to the traditional CMOS Terahertz detector, TFET-based one has faster response rate and higher detect efficiency, suggesting TFET a promising device for the low-power Terahertz imagin

Abstract-Measurement of Absorption Coefficient of Paraformaldehyde and Metaldehyde with Terahertz Spectroscopy

J. Zhang, T. Xia, Q. Chen, Q. Sun, Y. Deng, C. Wang, 

https://link.springer.com/article/10.1007/s10812-018-0616-6

The characteristic absorption spectra of paraformaldehyde and metaldehyde in the terahertz frequency region are obtained by terahertz time-domain spectroscopy (THz-TDS). In order to reduce the absorption of terahertz (THz) wave by water vapor in the air and the background noise, the measurement system was filled with dry air and the measurements were conducted at the temperature of 24°C. Meanwhile, the humidity was controlled within 10% RH. The THz frequency domain spectra of samples and their references from 0 to 2.5 THz were analyzed via Fourier transform. The refractive index and absorption coefficients of the two aldehydes were calculated by the model formulas. From 0.1 to 2.5 THz, there appear two weak absorption peaks at 1.20 and 1.66 THz in the absorption spectra of paraformaldehyde. Only one distinct absorption peak emerges at 1.83 THz for metaldehyde. There are significant differences between the terahertz absorption coefficients of paraformaldehyde and metaldehyde, which can be used as "fingerprints" to identify these substances. Furthermore, the relationship between the average absorption coefficients and mass concentrations was investigated and the average absorption coefficient–mass concentration diagrams of paraformaldehyde and metaldehyde were shown. For paraformaldehyde, there is a linear relationship between the average absorption coefficient and the natural logarithm of mass concentration. For metaldehyde, there exists a simpler linear relationship between the average absorption coefficient and the mass concentration. Because of the characteristics of THz absorption of paraformaldehyde and metaldehyde, the THz-TDS can be applied to the qualitative and quantitative detection of the two aldehydes to reduce the unpredictable hazards due to these substances.

Abstract-Identifying the perfect absorption of metamaterial absorbers

G. Duan, J. Schalch, X. Zhao, J. Zhang, R. D. Averitt, and X. Zhang

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.035128

We present a detailed analysis of the conditions that result in unity absorption in metamaterial absorbers to guide the design and optimization of this important class of functional electromagnetic composites. Multilayer absorbers consisting of a metamaterial layer, dielectric spacer, and ground plane are specifically considered. Using interference theory, the dielectric spacer thickness and resonant frequency for unity absorption can be numerically determined from the functional dependence of the relative phase shift of the total reflection. Further, using transmission line theory in combination with interference theory we obtain analytical expressions for the unity absorption resonance frequency and corresponding spacer layer thickness in terms of the bare resonant frequency of the metamaterial layer and metallic and dielectric losses within the absorber structure. These simple expressions reveal a redshift of the unity absorption frequency with increasing loss that, in turn, necessitates an increase in the thickness of the dielectric spacer. The results of our analysis are experimentally confirmed by performing reflection-based terahertz time-domain spectroscopy on fabricated absorber structures covering a range of dielectric spacer thicknesses with careful control of the loss accomplished through water absorption in a semiporous polyimide dielectric spacer. Our findings can be widely applied to guide the design and optimization of the metamaterial absorbers and sensors.

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Abstract-Terahertz emission driven by two-color laser pulses at various frequency ratios

W.-M. Wang, Z.-M. Sheng, Y.-T. Li, Y. Zhang, J. Zhang

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.96.023844

We present a simulation study of terahertz radiation from a gas driven by two-color laser pulses in a broad range of frequency ratios 

${\omega }_1/{\omega }_0$. Our particle-in-cell simulation results show that there are three series with ${\omega }_1/{\omega }_0=2n,n+1/2,n\pm 1/3$ ($n$ is a positive integer) for high-efficiency and stable radiation generation. The radiation strength basically decreases with the increasing ${\omega }_1$ and scales linearly with the laser wavelength. These rules are broken when ${\omega }_1/{\omega }_0<1$ and much stronger radiation may be generated at any ${\omega }_1/{\omega }_0$. These results can be explained with a model based on gas ionization by two linear-superposition laser fields, rather than a multiwave mixing model.

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Abstract-Terahertz emission driven by two-color laser pulses at various frequency ratios

W. -M. Wang, Z. -M. Sheng, Y. -T. Li, Y. Zhang, and J. Zhang

https://journals.aps.org/pra/accepted/e3073NbeQfc1301fb53673d6f1b3f282e85d2c8b0

We present a simulation study of terahertz radiation from a gas driven by two-color laser pulses in a broad range of frequency ratios \omega_1/\omega_0. Our particle-in-cell simulation results show that there are three series with \omega_1/\omega_0=2n, n+1/2, n\pm1/3 (n is a positive integer) for high-efficiency and stable radiation generation. The radiation strength basically decreases with the increasing \omega_1 and scales linearly with the laser wavelength. These rules are broken when \omega_1/\omega_0

Abstract-Terahertz emission from two-plasmon-decay induced transient currents in laser-solid interactions

G.-Q. Liao¹, Y.-T. Li^1,2,a), C. Li¹, S. Mondal³, H. A. Hafez³, M. A. Fareed³, T. Ozaki³, W.-M. Wang^1,2, Z.-M. Sheng^2,4,5,a) and J. Zhang^2,5
 http://scitation.aip.org/content/aip/journal/pop/23/1/10.1063/1.4939605?TRACK=RSS
a) Authors to whom correspondence should be addressed. Electronic addresses:ytli@iphy.ac.cn and zmsheng@sjtu.edu.cn
Phys. Plasmas 23, 013104 (2016); http://dx.doi.org/10.1063/1.4939605

We have studied the generation of terahertz (THz) radiation via the interaction of intense femtosecond laser pulses with solid targets at a small incidence angle. It is found that preplasma with a moderate density gradient can enhance the emission. We also observe saturation of the THz output with the driving laser energy. We find that THz emission is closely related to the 3/2 harmonics of the driving laser. Particle-in-cell simulations indicate that under the present experimental conditions, the THz emission could be attributed to the transientcurrents at the plasma-vacuum interface, mainly formed by the two-plasmon-decay instability.

Manipulating Light with a Single Layer of Carbon

My Note: This is somewhat old, but I include it because it's from the source for the most popular blog post found on this blog: "Viewpoint: Stimulated Near-Infrared Light Emission in Graphene".

"Femtosecond Population Inversion and Stimulated Emission of Dense Dirac Fermions in Graphene"

 http://www.ameslab.gov/research/highlights/manipulating-light-single-layer-carbon

 T. Li, L. Luo, M. Hupalo, J. Zhang, M.C. Tringides, J. Schmalian, and J. Wang 

Researchers have shown that it may be possible to make lasers using single-layer sheets of carbon atoms — the novel material known as graphene. Lasers are made from materials that can absorb ordinary light and then emit photons that have matching waves to provide high intensity.To generate laser power, a material must first undergo a population inversion where an excess of electrons is excited. They must then produce optical gain when one photon is emitted spontaneously causing the excited state electrons to undergo a cascade reaction, each one emitting an additional photon coherent with the first, so a large intensity builds up. Graphene exhibits both of these properties. Very short light pulses, only a few femtoseconds (10^-15 seconds) in duration, were used to stimulate the graphene. Almost instantaneously broad population inversions were observed; and the ultrabroad band gain is established at about 10 femtoseconds, producing a much wider tuning range of light (from terahertz to ultraviolet) than in conventional lasing materials. This is remarkable for photonics materials. Comparison of the experiments with newly-developed theoretical approaches neatly explains the findings. This work opens up a wide range of possible uses of graphene in previously-unexplored areas, particularly ultra-fast telecommunications and laser technology.With graphene a little light may go a long way