Abstract-Antireflection self-reference method based on ultrathin metallic nanofilms for improving terahertz reflection spectroscopy

Weien Lai, Haibing Cao, Jun Yang, Guangsheng Deng, Zhiping Yin, Qian Zhang, Beatriz Pelaz, and Pablo del Pino

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-15-19470

We present the potential of an antireflection self-reference method based on ultra-thin tantalum nitride (TaN) nanofilms for improving terahertz (THz) reflection spectroscopy. The antireflection self-reference method is proposed to eliminate mutual interference caused by unwanted reflections, which significantly interferes with the important reflection from the actual sample in THz reflection measurement. The antireflection self-reference model was investigated using a wave-impedance matching approach, and the theoretical model was verified in experimental studies. We experimentally demonstrated this antireflection self-reference method can completely eliminate the effect of mutual interference, accurately recover the actual sample’s reflection and improve THz reflection spectroscopy. Our method paves the way to implement a straightforward, accurate and efficient approach to investigate THz properties of the liquids and biological samples.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-A Tunable Polarization-Dependent Terahertz Metamaterial Absorber Based on Liquid Crystal

Guangsheng Deng, Yujiao Lu, Zhiping Yin,  Weien Lai, Hongbo Lu,  Jun Yang, Aifeng Yang, Yang Ye, Dayong Liu, Baihong Chi,

http://www.mdpi.com/2079-9292/7/3/27

In this paper, a tunable polarization-dependent terahertz (THz) metamaterial absorber based on liquid crystal (LC) is presented. The measurement results show that absorption peak is at 239.5 GHz for a TE-polarized wave and 306.6 GHz for a TM-polarized wave, without exerting the bias voltage on the LC layer. An increase in bias voltage affects the orientation of LC molecules and causes redshifted resonant frequencies. By adjusting the bias voltage from 0 to 10 V, frequency tunabilities of 4.7% and 4.1% for TE- and TM-polarized waves, respectively, were experimentally demonstrated. Surface current and power loss distribution was analyzed to explain the physical mechanism of the absorber, while the absorption dependence on geometrical parameters and incident angles was also studied in detail. According to the obtained results, the proposed absorber is shown here to be capable of achieving tunable polarization-dependent absorption, and to have potential application in terahertz polarization imaging, terahertz sensing, and polarization multiplexing

Abstract-Electrically tunable terahertz dual-band metamaterial absorber based on a liquid crystal

Zhiping Yin,  Yujiao Lu,  Tianyu Xia,  Weien Lai,  Jun Yang,  Hongbo Lua,  Guangsheng Deng,

http://pubs.rsc.org/en/content/articlelanding/2018/ra/c7ra13047c#!divAbstract

In this paper, a liquid crystal (LC) based tunable metamaterial absorber with dual-band absorption is presented. The proposed absorber is analysed both numerically and experimentally. The analysis shows that the two absorption peaks, originating from the new resonant structure, are experimentally detected at 269.8 GHz and 301.4 GHz when no bias voltage is applied to the LC layer. In order to understand the absorption mechanisms, simulation results for the surface current and power loss distributions are presented. Since liquid crystals are used as the dielectric layer to realize the electrically tunable absorber, a frequency tunability of 2.45% and 3.65% for the two absorption peaks is experimentally demonstrated by changing the bias voltage of the LC layer from 0 V to 12 V. Furthermore, the absorber is polarization independent and a high absorption for a wide range of oblique incidence is achieved. The designed absorber provides a way forward for the realization of tunable metamaterial devices that can be applied in multi-band detection and imaging.

Abstract-Enhanced All-Optical Modulation of Terahertz Waves Based on Manganese Ferrite Nanoparticles

Weien Lai, Peng Huang, Beatriz Pelaz, Pablo del Pino, and Qian Zhang

http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.7b07756?mi=aayia761&af=R&AllField=nano&target=default&targetTab=std

We present an all-optical modulator based on manganese ferrite nanoparticles (MnFe2O4 NPs), which provides an enhanced attenuation of broadband terahertz waves. A wide-band modulation of THz transmission was observed in a frequency range from 0.15 to 1.2 THz. The experimental results were assessed by simulations in the context of a band structure model of semiconductors. Our work demonstrated that coatings of MnFe2O4 NPs can be efficiently used to improve the performance of THz modulators based on optical modulation. This paper describes a new route to increase the surface photoconductivity of semiconductors by coating of MnFe2O4 NPs. This work demonstrates that the THz modulator based on MnFe2O4 NPs can significantly boost the overall performance of THz communication systems, and MnFe2O4 NPs may offer some useful solutions for future THz devices

Abstract-Enhanced Terahertz Radiation Generation of Photoconductive Antennas Based on Manganese Ferrite Nanoparticles

• Weien Lai
• , Oday Mazin Abdulmunem
• , Pablo del Pino
• , Beatriz Pelaz
• , Wolfgang J. Parak
• , Qian Zhang
•  & Huaiwu Zhang
• • 
    
  • http://www.nature.com/articles/srep46261

This paper presents a significant effect of manganese ferrite nanoparticles (MnFe2O4 NPs) on the increase of the surface photoconductivity of semiconductors. Herein, the optical characterization of photo-excited carriers of silicon coated with MnFe2O4 NPs was studied by using THz time-domain spectroscopy (THz-TDs). We observed that silicon coated with MnFe2O4 NPs provided a significantly enhanced attenuation of THz radiation in comparison with bare silicon substrates under laser irradiation. The experimental results were assessed in the context of a surface band structure model of semiconductors. In addition, photoconductive antennas coated with MnFe2O4 NPs significantly improved the efficiency of THz radiation generation and signal to noise ratio of the THz signal. This work demonstrates that coating with MnFe2O4 NPs could improve the overall performance of THz systems, and MnFe2O4 NPs could be further used for the implementation of novel optical devices.

Abstract-Broadband antireflection coating for optimized terahertz beam splitters

Weien Lai, Norman Born, Lorenz Maximilian Schneider, Arash Rahimi-Iman, Jan C. Balzer, and Martin Koch
https://www.osapublishing.org/ome/abstract.cfm?uri=ome-5-12-2812

We investigate the potential of anti-ferromagnetic nanofilms as broadband antireflection coatings in the terahertz frequency range. The anti-ferromagnetic layer is modeled by an analytic wave-impedance matching approach. The experimental results of the transmission and reflection measurements demonstrate the effectiveness of our antireflection coatings. Furthermore, we use anti-ferromagnetic nanofilms as antireflection coating for a terahertz beam splitter. Compared with conventional terahertz beam splitters consisting of an uncoated thick silicon wafer, the coated silicon beam splitter has two advantages: elimination of multiple reflections and improvement of the signal-to-noise ratio for terahertz time-domain spectroscopy in reflection geometry.

© 2015 Optical Society of America

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