Abstract-Seeing through a Black Box: Toward High-Quality Terahertz Tomographic Imaging via Multi-Scale Spatio-Spectral Image Fusion

 

Weng-tai Su, Ta-Hsuan Chao, Shang-Hua Yang, Chia-Wen Lin

https://arxiv.org/abs/2103.16932

Terahertz tomographic imaging has recently arisen significant attention due to its non-invasive, non-destructive, non-ionizing, material-classification, and ultrafast-frame-rate nature for object exploration and inspection. However, its strong water absorption nature and low noise tolerance lead to undesired blurring and distortion of reconstructed terahertz images. Research groups aim to deal with this issue through the use of synthetic data in the training phase, but still, their performances are highly constrained by the diffraction-limited terahertz signals. In this paper, we propose a novel multi-scale spatio-spectral fusion Unet (MS3-Unet) that extracts multi-scale features from the different spectral of terahertz image data for restoration. MS3-Unet utilizes multi-scale branches to extract spatio-spectral features which are then processed by element-wise adaptive filters, and then fused to achieve high-quality terahertz image restoration. Here, we experimentally construct ultra-high-speed terahertz time-domain spectroscopy system covering a broad frequency range from 0.1 THz to 4 THz for building up temporal/spectral/spatial/phase/material terahertz database of hidden 3-D objects. Complementary to a quantitative evaluation, we demonstrate the effectiveness of the proposed MS3-Unet image restoration approach on 3-D terahertz tomographic reconstruction applications.

Abstract-Navigating Terahertz Spectrum via Photomixing

Shang-Hua Yang and Mona Jarrahi

https://www.osapublishing.org/opn/abstract.cfm?uri=opn-31-7-36

Photomixers, including recent designs based on plasmonics, can combine tunability, power and room-temperature operation in both THz transmitters and receivers, for applications in 5G communications, astronomy and more.

© 2020 Optical Society of America

Abstract-Globally stable microresonator Turing pattern formation for coherent high-power THz radiation on-chip

Shu-Wei Huang, Jinghui Yang, Shang-Hua Yang, Mingbin Yu, Dim-Lee Kwong, T. Zelevinsky, Mona Jarrahi, and Chee Wei Wong

https://journals.aps.org/prx/accepted/44076K0cIb517709416d6635e46a4d487511ca7c6

In nonlinear microresonators driven by continuous-wave (cw) lasers, Turing patterns have been studied in the formalism of Lugiato-Lefever equation with emphasis on its high coherence and exceptional robustness against perturbations. Destabilization of Turing pattern and transition to spatio-temporal chaos, however, limits the available energy carried in the Turing rolls and prevents further harvest of their high coherence and robustness to noise. Here we report a novel scheme to circumvent such destabilization, by incorporating the effect of local mode hybridizations, and attain globally stable Turing pattern formation in chip-scale nonlinear oscillators with significantly enlarged parameter space, achieving a record high power conversion efficiency of 45{\%} and an elevated peak-to-valley contrast of 100. The stationary Turing pattern is discretely tunable across 430 GHz on a THz carrier, with a fractional frequency sideband non-uniformity measured at 7.3\texttimes 10}\mathbf{-14}{. We demonstrate the simultaneous microwave and optical coherence of the Turing rolls at different evolution stages through ultrafast optical correlation techniques. The free-running Turing roll coherence, 9 kHz in 200 ms and 160 kHz in 20 minutes, is transferred onto a plasmonic photomixer for one of the highest power THz coherent generation at room-temperature, with 1.1{\%} optical-to-THz power conversion. Its long-term stability can be further improved by more than two orders of magnitude, reaching an Allan deviation of 6\texttimes 10}\mathbf{-10}{ at 100 s, with a simple computer-aided ...

Researchers strive to channel the strength of terahertz waves

Mona Jarrahi, an associate professor of electrical engineering, leads the development of a new technology to create more sensitive detectors through terahertz waves. (Jennifer Hu/Daily Bruin staff)

BY BRIANNA CAMPBELL

 http://dailybruin.com/2016/10/13/researchers-strive-to-channel-the-strength-of-terahertz-waves/

A UCLA researcher is working to improve doctors’ abilities to detect tumors.

Mona Jarrahi, an electrical engineering associate professor and principal investigator of the Terahertz Electronics Laboratory, developed a new technology that converts light into high-powered radiation waves, called terahertz waves.

Jarrahi won the Popular Mechanics Breakthrough Award this year for her research, which may eventually lead to better imaging technology for detecting tumors and early signs of cancer.

[Related: UCLA to participate in new science and technology imaging center]

“Our lab is working with physicians to employ our technology for various medical imaging and diagnosis applications, including burn wound characterization and early stage detection of lung cancer and melanoma,” Jarrahi said.

Terahertz imaging can provide high contrast images that other technologies cannot, Jarrahi said.

“Terahertz technology has a lot of unique applications for imaging and sensing,” Jarrahi added. “One of the main problems that we have in this field is lack of high-power radiation sources and high sensitivity detectors to be able to do imaging and sensing in various settings.”

The device Jarrahi developed has high sensitivity detectors that allow researchers to see deeper into tissues, allowing them to study environments that weren’t easily accessed before.

Jarrahi added that researchers can also see new concentrations of chemicals with the terahertz radiation waves.

 For example, Jarrahi said the Terahertz Electronics Laboratory is collaborating with NASA’s Jet Propulsion Laboratory to detect chemicals in planetary gases.

[Related: Three UCLA engineering professors to be awarded highest honors for research]

Shang-Hua Yang, who works with Jarrahi in the lab, added the terahertz power level can also offer opportunities for agricultural inspection and pharmaceutical quality control.

Nezih Yardimci, a doctoral student in the electrical engineering and computer science department at the University of Michigan, Ann Arbor, has worked with Jarrahi in the lab for four years.

“She is well-versed in physical and wave electronics and taught me how to conduct more effective research, think innovatively and devote myself to what I do,” Yardimci said.

Jarrahi said the lab is working to make the terahertz imaging systems more compact and efficient. With that technology they hope to miniaturize the entire imaging system and create sensors small enough to fit in handheld devices like the iPhone.

“The general idea is to eventually design a handheld device (that can be used) for personal monitoring,” she said. “The great thing about terahertz waves is that they have very low energy compared to x-rays, so being exposed to these rays for long periods of time wouldn’t cause health problems, since they don’t harm the tissue.”

Jarrahi will continue to work to make the terahertz waves more sensitive so researchers will be able to accomplish new tasks – from making airport security sensors stronger to improving researchers’ ability to explore space.

Compact terahertz radiation source using a bimodal laser and plasmonic photomixer

http://spie.org/newsroom/technical-articles/6389-compact-terahertz-radiation-source-using-a-bimodal-laser-and-plasmonic-photomixer

Shang-Hua Yang, ReganWatts, Xiao Li, Ning Wang, Vivi Cojocaru, Liam Barry, James O’Gorman and Mona Jarrahs

Combining a plasmonic photomixer with a novel two-section digital distributed feedback laser diode enables generation of high-power, wavelength-tunable terahertz radiation at room temperature.

19 April 2016, SPIE Newsroom. DOI: 10.1117/2.1201603.006389

Terahertz waves offer unique opportunities in many fields. These include chemical sensing, material characterization, non-destructive diagnosis, medical imaging, and security screening. For many of these applications, however, practical feasibility is limited by low radiation power, narrow bandwidth, and the bulky nature of existing terahertz radiation sources.1

To address these limitations, we have recently demonstrated a compact terahertz source based on a novel two-section digital distributed feedback (D-DFB) laser diode and plasmonic photomixer. Our system generates terahertz radiation with 0.15–3THz frequency tunability, 2MHz linewidth, and less than 5MHz frequency stability over one minute, at power levels that can be used in practical imaging and sensing applications. We achieve terahertz wave generation through difference frequency generation, by pumping the plasmonic photomixer with two output optical beams from a two-section D-DFB laser diode.

Our two-section D-DFB laser diode—see Figure 1(a)—is a standard ridge waveguide laser diode, with a ridge width of 2.5um, which we fabricated on an indium phosphide substrate. The laser active region consists of five compressively strained aluminum gallium indium arsenide quantum wells with a well thickness of 5nm. The laser cavity is 700μm long and divided into two sections (with lengths of 400 and 300μm, respectively) that are separated by a 2μm-wide etched trench. The output beam is emitted from the first of these sections (section 1).

Figure 1. (a) Schematic diagram of the two-section digital distributed feedback laser diode. (b) The system's optical spectra at three different operating points. dBm: Decibel-milliwatts.

To achieve dual-mode output wavelengths, different features are etched into the ridge waveguide of each section to select two dynamically stable single lasing modes.2, 3 When both lasers are operated together, the coupling between the two laser cavities results in the generation of light at two wavelengths.4 In the meantime, we can tune the separation between the wavelengths by varying the temperature of the overall structure and the currents applied to the laser sections. The output spectra of the two-section D-DFB laser, at three specific operating points, are shown in Figure 1(b). With these operating conditions, we achieve spectral separations of 0.15, 1.62, and 2.99THz, and linewidths of about 1MHz.1

We used a plasmonic photomixer to convert the optical beam from the two-section D-DFB laser to terahertz radiation.5, 6 The photomixer comprises an ultrafast photoconductor, with plasmonic contact electrode gratings, integrated with a logarithmic spiral antenna on an erbium arsenide:indium gallium arsenide substrate, as shown in Figure 2(a). When the optical beam from the two-section D-DFB laser is incident on the anode plasmonic contact electrodes, a large fraction of the photogenerated carriers is generated in close proximity to the contact electrodes (as a result of the excitation of surface plasmon waves). By concentrating a major portion of the incident optical beam near the plasmonic contact electrodes, a large number of the photogenerated electrons drift to the anode plasmonic contact electrodes on a sub-picosecond timescale to efficiently contribute to terahertz radiation.5–11 We then feed the induced photocurrent to the logarithmic spiral antenna to generate terahertz radiation at the beating frequency of the two main spectral peaks of the two-section D-DFB laser. We use a fiber amplifier with a 2% duty cycle to amplify the laser output before coupling it to the plasmonic photomixer.

Figure 2. (a) Schematic diagram and scanning electron microscope images of the fabricated erbium arsenide:indium gallium arsenide (ErAs:InGaAs) plasmonic photomixer with plasmonic contact electrode gratings. (b) The radiated terahertz power at each continuous wave (CW) radiation cycle, as a function of frequency. (c) The radiated terahertz power at each CW radiation cycle as a function of the average optical pump power and bias voltage at 1.62THz.

The measured terahertz radiation power, as a function of frequency, is shown in Figure 2(b). These results indicate a broad radiation frequency tuning range of 0.15–3THz. At an average optical pump power of 100mW, we achieved terahertz radiation powers as high as 1.3mW, 106μW, and 12μW at each continuous wave radiation cycle at 0.44, 1.20, and 2.85THz, respectively. We also achieved higher terahertz radiation powers at higher optical pump powers, as illustrated in Figure 2(c). Linewidth measurements for the generated signals exhibit radiation linewidths of about 2MHz, with a frequency stability of less than 5MHz over a one-minute time frame.

In summary, we have demonstrated a novel compact terahertz radiation source that is based on a two-section D-DFB laser diode and plasmonic photomixer. The high power, broad frequency tunability, compact size, and robust operation of our terahertz source means that it offers a good solution for future high-performance terahertz imaging and sensing systems. In our future work, we will investigate the inclusion of plasmonic photomixing elements inside various types of bimodal lasers to offer a single-chip terahertz radiation source.

We gratefully acknowledge financial support from the Office of Naval Research, National Science Foundation, Army Research Office, Science Foundation Ireland Irish Photonic Integration Centre program, and the European Space Agency project Far IR Local Oscillator.

---

Shang-Hua Yang, Xiao Li, Ning Wang, Mona Jarrahi

University of California Los Angeles

Los Angeles, CA

Regan Watts, Vivi Cojocaru, Liam Barry

School of Electronic Engineering
Dublin City University

Dublin, Ireland

James O'Gorman

Xylophone Optics Ltd

Dublin, Ireland

---

References:

1. S.-H. Yang, R. Watts, X. Li, N. Wang, V. Cojocaru, J. O'Gorman, L. P. Barry, M. Jarrahi, Tunable terahertz wave generation through a novel bimodal laser diode and plasmonic photomixer, Opt. Express 23, p. 31206-31215, 2015.

2. J. Patchell, D. Jones, B. Kelly, J. O'Gorman, Specifying the wavelength and temperature tuning range of a Fabry-Perot laser containing refractive index perturbations, Proc. SPIE 5825, 2005. doi:10.1117/12.611334

3. B. Corbett, D. McDonald, Single longitudinal mode ridge waveguide 1.3 μm Fabry-Perot laser by modal perturbation, Electron. Lett. 31, p. 2181-2182, 1996.

4. J. Hong, R. Finlay, R. Tong, C. Rogers, D. Goodchild, Simultaneous dual-wavelength operation in cascaded strongly gain-coupled DFB lasers, IEEE Photon. Technol. Lett. 11, p. 1354-1356, 1999.

5. C. W. Berry, M. R. Hashemi, S. Preu, H. Lu, A. C. Gossard, M. Jarrahi, Plasmonics enhanced photomixing for generating quasi-continuous-wave frequency-tunable terahertz radiation, Opt. Lett. 39, p. 4522-4524, 2014.

6. C. W. Berry, M. R. Hashemi, S. Preu, H. Lu, A. C. Gossard, M. Jarrahi, High power terahertz generation using 1550 nm plasmonic photomixers, Appl. Phys. Lett. 105, p. 011121, 2014.

7. S.-H. Yang, M. Jarrahi, Enhanced light-matter interaction at nanoscale by utilizing high-aspect-ratio metallic gratings, Opt. Lett. 38, p. 3677-3679, 2013.

8. C. W. Berry, N. Wang, M. R. Hashemi, M. Unlu, M. Jarrahi, Significant performance enhancement in photoconductive terahertz optoelectronics by incorporating plasmonic contact electrodes, Nat. Commun. 4, p. 1622, 2013. doi:10.1038/ncomms2638

9. M. Jarrahi, Advanced photoconductive terahertz optoelectronics based on nano-antennas and nano-plasmonic light concentrators, IEEE Trans. Terahertz Sci. Technol. 5, p. 391-397, 2015.

10. N. T. Yardimci, S.-H. Yang, C. W. Berry, M. Jarrahi, High power terahertz generation using large area plasmonic photoconductive emitters, IEEE Trans. Terahertz Sci. Technol.5, p. 223-229, 2015.

11. S.-H. Yang, M. R. Hashemi, C. W. Berry, M. Jarrahi, 7.5% optical-to-terahertz conversion efficiency offered by photoconductive emitters with three-dimensional plasmonic contact electrodes, IEEE Trans. Terahertz Sci. Technol. 4, p. 575-581, 2014.

Prof. Jarrahi’s student Shang-Hua Yang invited to attend the 66th annual gathering of Nobel Laureates.

https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=7691909459918471195

Shang-Hua Yang, a Ph.D. student from Prof. Mona Jarrahi’s research group, has been invited to attend the 66th annual gathering of Nobel Laureates that takes place in Lindau, Germany from June 26 to July 1, 2016.

This is an annual event, gathering Nobel Laureates, in Lindau to meet the next generation of young scientists from all over the world. The attendees are selected based on their academic and research achievements through a rigorous and highly competitive process. Only the 400 most qualified young scientists from 80 countries are given the opportunity to enrich and share the unique atmosphere of the 2016 Lindau Nobel Laureate Meeting. The 2016 meeting is dedicated to the field of physics.

Shang-Hua has made significant contributions to the advancement of terahertz technology by developing innovative terahertz devices and systems. His exceptional academic performance has been recognized by several prestigious awards and scholarships including Taiwanese Government Studying Abroad Scholarship (2015), IEEE Antennas and Propagation Society Doctoral Research Award (2014), SPIE Graduate Scholarship (2012), etc.

Abstract-Spectral characteristics of terahertz radiation from plasmonic photomixers

Shang-Hua Yang and Mona Jarrahi
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-22-28522

We present a comprehensive analysis of spectral characteristics of terahertz radiation from plasmonic photomixers. We fabricate plasmonic photomixer prototypes with plasmonic contact electrode gratings on a low temperature grown GaAs substrate and characterize the spectral properties of the generated terahertz radiation by use of a heterodyne detection scheme. Our analysis shows that linewidth, stability, and frequency tuning range of the generated terahertz radiation are directly determined by linewidth, stability, and wavelength tuning range of optical pump beam and not affected by device geometry, substrate properties, optical pump power level and other operational settings. Our study indicates the crucial role of optical sources in realizing high performance terahertz spectroscopy and wireless communication systems based on plasmonic photomixers.

© 2015 Optical Society of America

Full Article  |  PDF Article

Abstract-Frequency-tunable continuous-wave terahertz sources based on GaAs plasmonic photomixers

Shang-Hua Yang^1,2 and Mona Jarrahi^1,2
 HIDE AFFILIATIONS
1 Electrical Engineering and Computer Science Department, University of Michigan, Ann Arbor, Michigan 48109, USA
2 Electrical Engineering Department, University of California Los Angeles, Los Angeles, California 90095, USA
Appl. Phys. Lett. 107, 131111 (2015); http://dx.doi.org/10.1063/1.4932114

http://scitation.aip.org/content/aip/journal/apl/107/13/10.1063/1.4932114

We present frequency-tunable, continuous-wave terahertz sources based on GaAs plasmonicphotomixers, which offer high terahertz radiation power levels at 50% radiation duty cycle. The use of plasmonic contact electrodes enhances photomixer quantum efficiency while maintaining its ultrafast operation by concentrating a large number of photocarriers in close proximity to the device contact electrodes. Additionally, the relatively high thermal conductivity and high resistivity of GaAs allow operation under high optical pump power levels and long duty cycles without reaching the thermal breakdown limit of the photomixer. We experimentally demonstrate continuous-wave terahertz radiation with a radiation frequency tuning range of more than 2 THz and a record-high radiation power of 17 μW at 1 THz through plasmonicphotomixers fabricated on a low temperature grown GaAs substrate at 50% radiation duty cycle.

Fully integrated broadband terahertz modulators

Mehmet Unlu, Mohammad Hashemi, Christopher Berry, Shenglin Li, Shang-Hua Yang and Mona Jarrahi,

http://spie.org/x110776.xml?highlight=x2406&ArticleID=x110776

Metasurfaces that can be reconfigured by microelectromechanical systems allow extreme switching in scattering parameters.

19 November 2014, SPIE Newsroom. DOI: 10.1117/2.1201410.005657

Recent advances in terahertz sources and detectors have made terahertz radiation much more accessible for many practical imaging and sensing applications, such as identifying chemicals, characterizing materials, biological sensing, and biomedical imaging, increasing demand for high-performance terahertz passive components. Among these, terahertz modulators play a key role in single-pixel compressive sensing and imaging systems,1, 2 especially when high-sensitivity detector arrays with a large number of pixels are not available.

It is challenging to construct high-performance terahertz modulators based on conventional optical and IR modulation schemes3–8 due to a lack of materials with the desired properties at terahertz frequencies and practical difficulties in scaling device dimensions to operate efficiently in this regime.9 In contrast, the spectral response of reconfigurable metamaterials (constructed by assembling so-called meta-molecule building blocks in a specific arrangement) can be engineered by their geometry, rather than being limited by the characteristics of natural materials at terahertz frequencies. As a result, they offer a very promising platform for manipulating terahertz waves.10, 11

However, until now the operational bandwidth of terahertz modulators based on metamaterials has been limited by the resonant nature of the device configurations employed. There is a good reason for using resonant structures in previously demonstrated reconfigurable metamaterials: the response is highly sensitive to small changes in the metamaterial's constituent parts as a result of external stimuli at resonance frequency.

To enable broadband modulation, we have developed a reconfigurable metasurface that, unlike previous attempts, offers extreme switching in the scattering parameters without use of any resonant enhancement within the device operation frequency range.12 Therefore, it enables the broadband modulation required in time-domain and frequency-tunable terahertz spectroscopy and imaging systems. Moreover, we achieved the demonstrated broadband switching of the scattering parameters through a fully integrated, electrically controlled, room-temperature platform, making it suitable for real-world, practical wave manipulation applications, such as portable sensors and imaging systems.

The metasurface consists of an array of microscale metallic islands integrated with an array of microelectromechanical systems (MEMS) switches (see Figure 1). Activating the MEMS switches brings the previously separate metallic islands into contact with each other. Their electromagnetic properties then change from a low pass (capacitive) filter to a high-pass (inductive) filter over a range of wavelengths that are much larger than the feature size and periodicity of the islands.12, 13 As a result, by shifting the MEMS switches between the contact and non-contact modes, their response to an incident electromagnetic wave changes from transmission to reflection, leading to efficient terahertz modulation over a broad range of frequencies determined by the meta-surface geometry.

 

Figure 1. Scanning electron microscopy images (above) and schematic diagram (below) of a microelectromechanical systems (MEMS)-reconfigurable metasurface that offers broadband terahertz modulation. E, H, KTHz: Electric field, magnetic field, and wave vector of the incident terahertz wave. Au: Gold. Si: Silicon. SiO2: Silicon dioxide.

We used the extraordinary switching of the scattering parameters of the presented metasurface to develop a fully integrated room-temperature terahertz intensity modulator. The modulator was fabricated on a high-resistivity silicon substrate and characterized in a time-domain terahertz spectroscopy setup exhibiting terahertz intensity modulation with record high modulation depths (>70%) and modulation bandwidths (>1.5THz). The high modulation depth of the presented modulator offers higher signal-to-noise ratio levels in single-pixel compressive sensing and imaging systems. Additionally, its broad modulation bandwidth makes it compatible with time-domain and frequency-tunable terahertz spectroscopy and imaging systems. We are now working on miniaturizing the reconfigurable metasurface to extend the terahertz modulator's bandwidth beyond 1.5THz. We are also working on improving the yield of the MEMS switch arrays to further increase the device modulation depth beyond 70%.

We gratefully acknowledge financial support from the National Science Foundation Sensor and Sensing Systems division (1030270) and Army Research Office Young Investigator Award (W911NF-12-1-0253).

---

Mehmet Unlu, Mohammad Hashemi, Christopher Berry, Shenglin Li, Shang-Hua Yang, Mona Jarrahi

Electrical Engineering and Computer Science Department University of Michigan

Ann Arbor,

---

References:

1. W. L. Chan, M. L. Moravec, R. G. Baraniuk, D. M. Mittleman, Terahertz imaging with compressed sensing and phase retrieval, Opt. Lett. 33, p. 974-976, 2008.

2. W. L. Chan, K. Charan, D. Takhar, K. F. Kelly, R. G. Baraniuk, D. M. Mittleman, A single-pixel terahertz imaging system based on compressed sensing, Appl. Phys. Lett. 93, p. 121105, 2008.

3. A. Liu, R. Jones, L. Liao, D. Samara-Rubio, D. Rubin, O. Cohen, R. Nicolaescu, M. Paniccia, A high-speed silicon optical modulator based on a metal-oxide-semiconductor capacitor, Nature 427, p. 615-618, 2004.

4. M. Liu, X. Yin, E. Ulin-Avila, B. Geng, T. Zentgraf, L. Ju, F. Wang, X. Zhang, A graphene-based broadband optical modulator, Nature 474, p. 64-67, 2011.

5. M. Jarrahi, T. H. Lee, D. A. B. Miller, Wideband, low driving voltage traveling wave Mach-Zehnder modulator for RF photonics, Photon. Technol. Lett. 20, p. 517, 2008.

6. W. E. Ross, D. Psaltis, R. H. Anderson, Two-dimensional magneto-optic spatial light modulator for signal processing, Opt. Eng. 22, p. 485-490, 1983.

7. O. Solgaard, F. S. A. Sandejas, D. M. Bloom, Deformable grating optical modulator, Opt. Lett. 17, p. 688-690, 1992.

8. M. Jarrahi, R. F. W. Pease, D. A. B. Miller, T. H. Lee, Optical switching based on high-speed phased-array optical beam steering, Appl. Phys. Lett. 92, p. 014106, 2008.

9. M. Rahm, J.-S. Li, W. J. Padilla, THz wave modulators: a brief review on different modulation techniques, J. Infrared Milli. Terahz. Waves 34, p. 1-127, 2012.

10. H. Tao, W. J. Padilla, X. Zhang, R. D. Averitt, Recent progress in electromagnetic metamaterial devices for terahertz applications, IEEE J. Sel. Top. Quant. Electron. 17, p. 92-101, 2011.

11. H. Tao, A. C. Strikwerda, K. Fan, W. J. Padilla, X. Zhang, R. D. Averitt, Reconfigurable terahertz metamaterials, Phys. Rev. Lett. 103, p. 147401, 2009.

12. M. Unlu, M. R. Hashemi, C. W. Berry, S. Li, S.-H. Yang, M. Jarrahi, Switchable scattering meta-surfaces for broadband terahertz modulation, Nat. Sci. Rep. 4, p. 5708, 2014.

13. C. W. Berry, J. Moore, M. Jarrahi, Design of reconfigurable metallic slits for terahertz beam modulation, Opt. Exp. 19, p. 1236-1245, 2011.