Abstract-High-responsivity and polarization-discriminating terahertz photodetector based on plasmonic resonance

Applied Physics Letters

Yuanliao Zheng, Pingping Chen, Heming Yang, Jiayi Ding, Yuwei Zhou, Zhou Tang, Xiaohao Zhou, Zhifeng Li, Ning Li,  Xiaoshuang Chen, Wei Lu,

(a) The structure of the SPQWP device; (b) the schematic view of the periodic units for the SPQWP structure

https://aip.scitation.org/doi/abs/10.1063/1.5085813

In this paper, a high-responsivity terahertz quantum well photodetector based on plasmonic resonance is proposed and investigated theoretically and experimentally, and the polarization-discriminating detection of the device is demonstrated. With a one-dimensional metallic grating structure integrated on the top of the detector, a 6-fold enhancement of the peak responsivity about 0.82 A/W at 46 μm compared to that of the standard device has been achieved. The physical mechanism behind the enhanced responsivity can be attributed to the enhancement of the intersubband absorption resulting from the surface Plasmon polariton mode, which can be explored from the theoretical simulation results. The polarization extinction ratio of the plasmonic-enhanced device reaches 56, and the measured signal intensity at each polarization angle satisfies Malus' law. In addition to the above advantages, the structure is simple in fabrication and compatible with the preparation process of the focal plane array. The results open up an effective method for the application of surface plasmon in terahertz detection.

Characterizing PM2.5 in Beijing and Shanxi Province using terahertz radiation

Ning Li, Honglei Zhan, Kun Zhao, Zhenwei Zhang, Chenyu Li, Cunlin Zhang,

http://link.springer.com/article/10.1007/s12200-016-0608-1

Particles of aerodynamic diameter⩽2.5 µm (PM2.5) caused extremely severe and persistent haze pollution is of concern in many cities. In this study, samples of PM2.5 were collected from atmosphere environment of Beijing and Shanxi Province, and analyzed using terahertz (THz) radiation. The transmission spectrum of PM2.5 in Shanxi Province had two distinct absorption peaks at 6.0 and 6.7 THz, and the curve was increasing on the whole. However, the transmission spectrum of PM2.5 in Beijing had obviously different variation tendency and the absorption peak was studied by monitoring PM2.5 masses in conjunction with two-dimensional correlation spectroscopy (2DCOS). By comparing the pollutant species and concentrations of Shanxi Province and Beijing over the time of collecting samples, the concentrations of sulfate and ammonium were similar, which contributed to emerge absorption bands in the same position. While the concentrations of organic matter (OM), nitrate, chloride and elemental carbon (EC) were different. Furthermore, dust and some other inorganic ion are unique to Shanxi province, which lead to different variation tendency of the transmission spectrum of PM2.5. These results will be of importance for environmental monitoring and for controlling PM emissions. According to this research, optical techniques, and especially spectral methods, should be considered for PM2.5 monitoring.

Abstract-The effect of infrared plasmon on the performance of Si-based THz detectors

He Zhu, Jintao Xu, Jiaqi Zhu, Miao Wang, Huizhen Wu, Ning Li, Ning Dai

http://link.springer.com/article/10.1007/s10854-016-5598-7

Plasmons in metals have great impact on light emission, propagation, and detection in visible and infrared light wave frequencies. To explore plasmonic effect on the THz detection, both a backside-illuminated and a topside-illuminated blocking impurity band (BIB) THz detectors are developed and significant influence of plasmonic effect on the performance of BIB THz detectors is observed. The plasmonic effect in the heavily doped semiconductor layer of BIB THz detectors causes high reflectance of THz radiation which curtails the detection frequencies of the backside-illuminated BIB detectors. However, due to the advantages of flip-chip package and high quantum efficiency, the dark current, the responsivity, and the detectivity of the backside-illuminated detector shows superior characteristics to the topside-illuminated detector. The performance of the THz detector could be further improved with the suppression of the plasmonic effect.

Abstract-Energy scaling of terahertz-wave parametric sources

Energy scaling of terahertz-wave parametric sources Guanqi Tang, Zhenhua Cong, Zengguang Qin, Xingyu Zhang, Weitao Wang, Dong Wu, Ning Li, Qiang Fu, Qingming Lu, and Shaojun Zhang  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-23-4-4144

Optics Express, Vol. 23, Issue 4, pp. 4144-4152 (2015)
http://dx.doi.org/10.1364/OE.23.004144

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Terahertz-wave parametric oscillators (TPOs) have advantages of room temperature operation, wide tunable range, narrow line-width, good coherence. They have also disadvantage of small pulse energy. In this paper, several factors preventing TPOs from generating high-energy THz pulses and the corresponding solutions are analyzed. A scheme to generate high-energy THz pulses by using the combination of a TPO and a Stokes-pulse-injected terahertz-wave parametric generator (spi-TPG) is proposed and demonstrated. A TPO is used as a source to generate a seed pulse for the surface-emitted spi-TPG. The time delay between the pump and Stokes pulses is adjusted to guarantee they have good temporal overlap. The pump pulses have a large pulse energy and a large beam size. The Stokes beam is enlarged to make its size be larger than the pump beam size to have a large effective interaction volume. The experimental results show that the generated THz pulse energy from the spi-TPG is 1.8 times as large as that obtained from the TPO for the same pumping pulse energy density of 0.90 J/cm² and the same pumping beam size of 3.0 mm. When the pumping beam sizes are 5.0 and 7.0 mm, the enhancement times are 3.7 and 7.5, respectively. The spi-TPG here is similar to a difference frequency generator; it can also be used as a Stokes pulse amplifier.

© 2015 Optical Society of America

Abstract-Terahertz parametric oscillator based on KTiOPO4 crystal

Weitao Wang, Zhenhua Cong, Xiaohan Chen, Xingyu Zhang, Zengguang Qin, Guanqi Tang, Ning Li, Cong Wang, and Qingming Lu  »View Author Affiliations

Optics Letters, Vol. 39, Issue 13, pp. 3706-3709 (2014)
http://dx.doi.org/10.1364/OL.39.003706

https://www.blogger.com/blogger.g?blogID=124073320791841682&pli=1#editor/target=post;postID=8620925169788540846

KTiOPO4 (KTP) crystal is used as the nonlinear medium in a surface-emitted terahertz-wave parametric oscillator for the first time. The oscillating Stokes beam propagates along the x axis of the KTP crystal, the pumping beam propagates with a small incident angle θext to the x axis, and the polarizations of the pumping beam, the Stokes beam, and the THz wave are along the z axis. When θext is changed from 1.250° to 6.000°, the THz wave is intermittently tuned from 3.17 to 3.44 THz, from 4.19 to 5.19 THz, and from 5.55 to 6.13 THz. The maximum output of the THz wave is 336 nJ, obtained at 5.72 THz with a pumping energy of 80 mJ. The two frequency gaps, from 3.44 to 4.19 THz and from 5.19 to 5.55 THz, are located in the vicinities of the A1 modes of 134 and 178.7  cm−1, which are strongly infrared absorbing.

© 2014 Optical Society of America