Abstract-Ultimate terahertz field enhancement of single nanoslits

Young-Mi Bahk, Sanghoon Han, Jiyeah Rhie, Joohyun Park, Hyeongtag Jeon, Namkyoo Park, and Dai-Sik Kim

Phys. Rev. B 95, 075424

http://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.075424

A single metallic slit is the simplest plasmonic structure for basic physical understanding of electromagnetic field confinement. By reducing the gap size, the field enhancement is expected to first go up and then go down when the gap width becomes subnanometer because of the quantum tunneling effects. A fundamental question is whether we reach the classical limit of field enhancement before entering the quantum regime, i.e., whether the quantum effects undercut the highest field enhancement classically possible. Here, by performing terahertz time domain spectroscopy on single slits of widths varying from 1.5 nm to 50 µm, we show that ultimate field enhancement determined by the wavelength of light and film thickness can be reached before we hit the quantum regime. Our paper paves way toward designing a quantum plasmonic system with maximum control yet without sacrificing the classical field enhancements.

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Abstract-Graphene-based reconfigurable terahertz plasmonics and metamaterials

Sara Arezoomandan^a, 

Hugo O. Condori Quispe^a, 

Nicholas Ramey^b, 

Cesar A. Nieves^c, 

Berardi Sensale-Rodriguez

http://www.sciencedirect.com/science/article/pii/S000862231630985X

This work discusses and compares two proposed practical approaches for realizing graphene-based reconfigurable terahertz metamaterials, namely: graphene-only plasmonic structures, and graphene/metal hybrid structures. From rigorous theoretical analysis, full-wave electromagnetic numerical simulations, as well as supporting experiments, several reconfigurable structures are analyzed and compared in terms of their: (i) Quality-factor, (ii) Extinction-ratio, (iii) Unit-cell dimensions, and (iv) Resonance-frequency tunability-range. From this analysis it is observed that at terahertz frequencies, although typically possessing larger unit-cell dimensions and being limited by a restricted resonance-frequency tunability-range, reconfigurable metamaterials based on graphene/metal hybrid structures can provide much larger quality-factors, extinction levels, and, when reconfigured, smaller extinction-level degradation than graphene-only plasmonic structures. As a result, when analyzed in the context of reconfigurable terahertz metamaterials, graphene might result attractive as a reconfigurable media providing tunability to otherwise passive metallic structures rather than as a reconfigurable plasmonic material per-se.

Abstract-Plasmonic enhancement of sensitivity in terahertz (THz) photo-conductive detectors

Oleg Mitrofanov; Ting Shan Luk; Igal Brener; John L. Reno

http://spie.org/Publications/Proceedings/Paper/10.1117/12.2188177

We demonstrate enhancement of sensitivity in terahertz photoconductive detectors achieved by incorporation of plasmonic structures into the photo-conductive region of the detector. Auston switches based on lowtemperature grown GaAs (LT GaAs) have been reliably used for detection of THz pulses over two decades. This material exhibits high electron mobility with sub-picosecond carrier lifetimes and high dark resistivity. This combination is difficult to achieve in other materials. Application of LT GaAs in THz devices is nevertheless limited due to absorption characteristics of this material. Plasmonic structures can be employed to modify the distribution of the optical field in the photoconductive region and hence modify the response of the THz photoconductive detectors. We will discuss design of plasmonic structures to enhance the response of THz detectors based on LT GaAs and demonstrate incorporation of such structures into THz detectors. We also apply the developed design in integrated photo-conductive probes for THz near-field microscopy, where the enhancement of the material absorption translates into an increase of the detector sensitivity and an improvement in spatial resolution. Performance on these near-field probes that provide a spatial resolution of 3- 5 micrometers (~1/100 of the wavelength) will be discussed and demonstrated.

Abstract-Current-driven detection of terahertz radiation using a dual-grating-gate plasmonic detector

S. Boubanga-Tombet^1,a), Y. Tanimoto¹, A. Satou¹, T. Suemitsu¹, Y. Wang²,H. Minamide², H. Ito², D. V. Fateev^3,4, V. V. Popov^3,4 and T. Otsuji¹
 HIDE AFFILIATIONS
1 Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-Ku, Sendai 980-8577, Japan
2 RIKEN Sendai, 519-1399 Aramaki Aoba, Aoba-ku, Sendai 980-0845, Japan
3 Kotelnikov Institute of Radio Engineering and Electronics (Saratov Branch), 410019 Saratov, Russia
4 Saratov State University, 410012 Saratov, Russia
a) Author to whom correspondence should be addressed. Electronic mail: stephanealbon@hotmail.com
Appl. Phys. Lett. 104, 262104 (2014); http://dx.doi.org/10.1063/1.4886763

We report on the detection of terahertz radiation by an on-chip planar asymmetric plasmonicstructure in the frequency region above one terahertz. The detector is based on a field-effect transistor that has a dual grating gate structure with an asymmetric unit cell, which provides a geometrical asymmetry within the structure. Biasing the detector with a dc source-to-drain current in the linear region of the current-voltage characteristic introduces an additional asymmetry (electrical asymmetry) that enhances the detector responsivity by more than one order of magnitude (by a factor of 20) as compared with the unbiased case due to the cooperative effect of the geometrical and electrical asymmetries. In addition to the responsivity enhancement, we report a relatively low noise equivalent power and a peculiar non-monotonic dependence of the responsivity on the frequency, which results from the multi-plasmonic-cavity structure of the device.

Terahertz Plasmonic Structures with Varying Conductivities

By: Eva Rittweger
http://www.materialsviews.com/terahertz-plasmonic-structures-with-varying-conductivities/

With the ongoing desire to create devices and systems at ever increasing speeds, there is great interest in developing technology that operates at terahertz (THz) frequencies (1 THz = 1000 GHz). Plasmonics offers an excellent platform to create such devices, since metals exhibit extremely low loss in this frequency range. Most plasmonic structures are made by using a homogeneous metal film and then patterning it with an appropriate geometry. In order to broaden the operational capabilities of such devices, it would be advantageous to vary the conductivity of the metal film spatially.

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Credit: Photo credit: Dan Hixson, University of Utah College of Engineering.

Using a commercially available desktop inkjet printer equipped with conductive metal ink and resistive carbon ink, rather than the usual color inks, Ajay Nahata and co-workers (University of Utah) demonstrate a silver film with spatially varying conductivity.  They examined the effect of this added variation on the beam properties of freely propagating THz radiation. Their results demonstrate that this approach has great potential for creating entirely new families of plasmonic devices.

Abstract-Efficient terahertz electro-absorption modulation employing graphene plasmonic structures

http://arxiv.org/abs/1211.4176
 Berardi Sensale-Rodriguez, Rusen Yan, Mingda Zhu, Debdeep Jena, Lei Liu, Huili Grace Xing

We propose and discuss terahertz electro-absorption modulators based on graphene plasmonic structures. The active device consists of a self-gated pair of graphene layers, which are patterned to structures supporting THz plasmonic resonances. These structures allow for efficient control of the effective THz optical conductivity, thus absorption, even at frequencies much higher than the Drude roll-off in graphene where most previously proposed graphene-based devices become inefficient. Our analysis shows that reflectance-based device configurations, engineered so that the electric field is enhanced in the active graphene pair, could achieve very high modulation-depth, even ~100%, at any frequency up to tens of THz.