Large-Area Low-Cost Plasmonic Perfect Absorber Chemical Sensor Fabricated by Laser Interference Lithography

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Bagheri et al. (2016) employ laser interference lithography as a reliable and low-cost fabrication method to create nanowire and nanosquare arrays in photopolymers for manufacturing plasmonic perfect absorber sensors over homogeneous areas as large as 5.7 cm2. Subsequently, they transfer the fabricated patterns into a palladium layer by using argon ion beam etching. Geometry and periodicity of their large-area metallic nanostructures are precisely controlled by adjusting the interference conditions during single- and double-exposure processes, resulting in active nanostructures over large areas with spectrally selective perfect absorption of light from the visible to the near-infrared wavelength range. In addition, they demonstrate the method’s applicability for hydrogen detection schemes by measuring the hydrogen sensing performance of our polarization independent palladium-based perfect absorbers. Since palladium changes its optical and structural properties reversibly upon hydrogenation, exposure of the sample to hydrogen causes distinct and reversible changes within seconds in the absorption of light, which are easily measured by standard microscopic tools. The fabricated large-area perfect absorber sensors provide nearly perfect absorption of light at 730 and 950 nm, respectively, and absolute reflectance changes from below 1% to above 4% in the presence of hydrogen. This translates to a relative signal change of almost 400%. The large-area and fast manufacturing process makes our approach highly attractive for simple and low-cost sensor fabrication, and therefore, suitable for industrial production of plasmonic devices in the near future.



Infrared Plasmonic Biosensor for Real-Time and Label-Free Monitoring of Lipid Membranes




Odeta Limaj et al., report infrared plasmonic biosensor for real-time and lable-free monitoring of lipid membranes.

In this work, they present an infrared plasmonic biosensor for chemical-specific detection and monitoring of biomimetic lipid membranes in a label-free and real-time fashion. Lipid membranes constitute the primary biological interface mediating cell signaling and interaction with drugs and pathogens. By exploiting the plasmonic field enhancement in the vicinity of engineered and surface-modified nanoantennas, the proposed biosensor is able to capture the vibrational fingerprints of lipid molecules and monitor in real time the formation kinetics of planar biomimetic membranes in aqueous environments. Furthermore, they show that this plasmonic biosensor features high-field enhancement extending over tens of nanometers away from the surface, matching the size of typical bioassays while preserving high sensitivity.



Odeta LimajDordaneh EtezadiNathan J. WittenbergDaniel RodrigoDaehan YooSang-Hyun Oh, and Hatice Altug– Nano Lett., 2016, 16 (2), pp 1502–1508

DOI: 10.1021/acs.nanolett.5b05316

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Plasmonic Lasers Get a Sharper Focus

Plasmonic Lasers Get a Sharper Focus



In the Lehigh team’s “antenna feedback” approach, the plasmonic-laser cavity is enclosed between two metal films, with periodic slits on the top film. One SPP wave is confined inside the 10-micron-thick cavity; the other, with a larger spatial extent, is located on top of the cavity and coupled both to it and the far field, allowing a strong, narrow-beam emission. [Image: Sushil Kumar]

Lasers based on coherent surface plasmon polaritons (SPPs)—subwavelength oscillations of electrons that are excited when incident light hits a metal-dielectric interface—hold promise for ultraminiaturized, chip-scale optics, and also as a possible platform for terahertz quantum cascade lasers (QCLs). But there’s a catch: SPP lasers, precisely because of their subwavelength apertures, tend to have divergent radiation patterns, making it tough to produce a sharp, directional beam.

Now, a research team led by Sushil Kumar of Lehigh University, Penn., USA, has devised an “antenna feedback” scheme that reportedly can provide single-mode operation and strong, highly directional far-field coupling in such SPP lasers, bringing them “closer to practical applications” (Optica, doi:10.1364/OPTICA.3.000734). The team’s work includes a proof-of-concept terahertz QCL based on the scheme that, according to the study, achieved the narrowest beam yet reported for such a QCL.

The pros and cons of “spasers”

SPP lasers—also called plasmonic lasers or “spasers”—operate by confining light energy as coherent SPP oscillations in subwavelength cavities (commonly parallel-plate Fabry-Perot-type cavities in with a length greater than the subwavelength cavity width). Their subwavelength dimensions make these lasers intriguing for certain applications in integrated photonics and nanophotonics. Parallel-plate cavities with SPP modes are also used for terahertz QCLs (which have some interesting potential applications in biosensing and standoff detection of dangerous materials), as they can show low-threshold, high-temperature performance at those frequencies.

It turns out, however, that it’s difficult to extract light from the plasmonic energy trapped in the spaser cavity. And when light can be made to leak out, it tends to be low in power and highly divergent, which limits its usefulness in actual applications.

A plasmonic phased array?

Kumar’s team found a potential solution through a distributed-feedback approach that the team has dubbed “antenna feedback,” and that Kumar compares to the action of phased-array antennas in microwave communication systems. The team demonstrated by numerical modeling that a grating of slits on one side of the subwavelength Fabry-Perot resonator, spaced at a specific value, would allow a single SPP mode within the cavity to diffract outside of the cavity in the surrounding medium, through Bragg diffraction. The energy outside of the cavity builds up with positive feedback (again the result of the selection of the grating period).

As a result, a second intense SPP wave develops in the medium outside of the cavity that remains coupled to the cavity’s metal cladding but also can form a highly directional beam outside of it. “The narrow-beam emission,” the team writes, “is due in part to the cavity acting like an end-fire phased-array antenna at microwave frequencies.”

In a proof of concept, the team implemented the antenna-feedback scheme in a terahertz QCL, using a box-shaped cavity consisting of two 100-µm by 1400-µm metallic plates, separated by a distance of 10 µm. The researchers report that the resulting laser showed a beam divergence as small as 4 degrees by 4 degrees—“the narrowest beam reported for any terahertz QCL to date,” according to the study.

Applications in security and elsewhere

The researchers note that terahertz QCLs in particular have some interesting applications in security and standoff detection. At a recent innovation conference, they pointed out that “approximately 80 to 95 percent of explosives, and all commonly used ones, have unique and identifiable terahertz signatures.”

But, while their experiments focused particularly on terahertz QCLs, they stress that the antenna-feedback scheme should be applicable to plasmonic lasers of any operating wavelength that operate with Fabry-Perot cavities. That, in turn, could aid help make other applications of plasmonic lasers, in areas such as nanophotonics, more feasible, according to the scientists.

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Self-consistent description of graphene quantum amplifier


The development of active and passive plasmonic devices is challenging due to the high level of dissipation in normal metals. One possible solution to this problem is using alternative materials. Graphene is a good candidate for plasmonics in the near-infrared region. In this paper, we develop a quantum theory of a graphene plasmon generator. Lozovic et al. account for quantum correlations and dissipation effects, thus they are able to describe such regimes of a quantum plasmonic amplifier as a surface plasmon emitting diode and a surface plasmon amplifier using stimulated radiation emission. Switching between these generation types is possible in situ with a variance of the graphene Fermi level. They provide explicit expressions for dissipation and interaction constants through material parameters, and they identify the generation spectrum and the second-order correlation function, which predicts the laser statistics.



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