Controlled steering of Cherenkov surface plasmon wakes with a one-dimensional metamaterial

Why not investigate wakes in plasmonics, such as Cherenkov waves, well-known from the acoustic bang that occurs when a jet-plane breaks the ultrasonic barrier? Patrice Genevet, Federico Capasso, et al. investigated such “supersonic” plasmon waves and present it in their talk at the CLEO 2015 conference. They excite the required plasmonic waves with specifically arranged small slit antennas in a metal film such as to design the phase of the plasmons that are excited and run along the metal surface. They generate waves whose phase velocity is higher than the waves supported by the unchanged standard interface. With resonator geometries and near-field scanning optical microscopy (NSOM) they then are able to observe Cherenkov waves, which they boldly call “super plasmonic waves”, in reminiscence of “super sonic waves”.

The key component of the experiments is indeed an experimental configuration that the authors around Federico Capasso recently introduced and published as a tool for versatile wavefront control: Arrays of short, small, deeply sub wavelength slits that are fabricated with FIB into a metal film[1][2]. Depending on the angle of those effective antennas that varies along the antenna array it is possible to shape the phase of the running wave with high versatility, fundamentally as a superposition of many, tilted SPP sources. Searching for alternative applications, the group discovered the challenging idea of generating plasmonic Cherenkov waves.

The results were very well perceived by the audience. However, a critical comment highlighted that the system indeed has a quite important difference from acoustic Cherenkov waves. The waves emerge from the antenna array that is not moving in space. This is what makes Cherenkov waves in acoustics interesting. Hence, even as the effects are quite interesting as a playground application of a very interesting method, applications are not obvious. Anyway, it is a very nice demonstration of what is ultimately possible with free wave phase design in plasmonics.



  1. N. Yu, and F. Capasso, "Flat optics with designer metasurfaces", Nature Materials, vol. 13, pp. 139-150, 2014.
  2. N. Yu, P. Genevet, M.A. Kats, F. Aieta, J. Tetienne, F. Capasso, and Z. Gaburro, "Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction", Science, vol. 334, pp. 333-337, 2011.

Nanophotonic metastructures: Functionality at the extreme

Nader Engheta of University of Pennsylvania.

Nader Engheta of University of Pennsylvania.

Nader Engheta from the University of Pennsylvania gives an excellent overview talk of his metamaterial lumped circuit approach and what he calls “metatronics” to explain and analyze how light behaves in complex, coupled nanophotonic structures below the wavelength of light.

This approach has during the last years proven to be powerful enough to open even new approaches to previously seemingly well-known systems. This might be the reason why his talk is stuffed with scientists eager to learn about his most recent findings. Based on this approach Engheta suggested investigating epsilon-near-zero (ENZ) systems, solutions for optical cloaking and generally optical systems that are extreme in space, spectrally and in time.

Graphene is such an example for an extreme material in space. One single atom thin layer. Optically combinations of materials with graphene can in fact be described as a metamaterial that offers interesting properties and a whole plethora of different results on the topic were already shown on this conference. Engheta now combines two different systems: Wrapping a single atomic thin graphene layer around an optical fiber makes the thin layer act as a metamaterial. The light that propagates through the optical fiber interacts with the graphene layer as it travels along a taper and is successively increasingly laterally confined. However, the electromagnetic field that travels along such a fiber usually cannot be focused lower than slightly below the Abbe diffraction limit, a value that is given by the effective index of the mode that is itself determined by the refractive index of the medium. In case of glass in the visible range, this index hence the confinement-enhancement factor can only be slightly larger than 1.4. Now wrap a layer of single atomic graphene around such an optical fiber as it is tapered to a very low diameter. Even if the diameter becomes much smaller than the free-space wavelength of the light, the wrapped fiber still acts as an efficient, highly confining waveguide.

As a last, but definitely one of the most exciting applications, Engheta treats the task of information processing with metamaterials. This is an approach that differs a lot from the sequential binary information processing in electronic micro circuits. Metatronics is the term that Engheta phrases to cover the approach. He makes a reference to original analog computing machines, room-large devices that were used in the time before the advent of today’s efficient binary computing machines. Those systems, although being bulky and complicated, were very efficient in solving specialized tasks, e.g. mathematics with derivations. Actually, nowadays we observe again an increasing interest deviating from the obiquitous multi-purpose processing devices that usually form the central processing unit (CPU) of computers: Highly parallelized graphical computing units (GPU) calculate your images for the computer screens. ASIC systems are e.g. used to effieciently mine bit coins. Those electronic processing devices are specialized, but still binary.

Engheta predicts that highly parallelized, highly efficient, but very specialized analog, optical metamaterial data processing devices might in the short future become really useful. Signals that are already optical can be processed with this approach in its native form and basically with the speed of light. He recently drafted several possible approaches in a Science article[1].



  1. A. Silva, F. Monticone, G. Castaldi, V. Galdi, A. Alu, and N. Engheta, "Performing Mathematical Operations with Metamaterials", Science, vol. 343, pp. 160-163, 2014.

Eric Betzig on near-field microscopy and superresolution

2014 was a year of plenty of Nobel prizes for the optics community. Eric Betzig describes his development from optics with an interest in bio-imaging, via a number of detours and mechanical engineering back to microscopy and ultimately to his Nobel prize.

His initial work was indeed already on nano imaging with near-field optical microscopy, starting during his graduate studies, leading him to Bell labs and in fact he discovered there some of the techniques that I am currently using in my research[1].

After some time off science, he returned, when he saw that it had become possible to implement green bio fluorescence into living cells[2]. This made it possible to actually map molecules in living cells under the microscope. While electron microscopes are and have for a long time been the first choice for imaging dead material, for imaging live cells, a high vacuum environment is no choice. Optics is the method to use. The connection to the approach of Stefan Hell, introduced in his earlier talk today, becomes clear there. Nano resolution imaging inside cells became possible[3].

In fact, a basic problem with the described methods is, while they reach very high resolution with even biological samples, they are slow. Being slow is a problem when the aim is imaging moving cells. Increasing the power is not helpful either, as this grills the cells faster. Betzig emphasizes that his methods are not actually ideal regarding that tradeoff.

The acronym of these methods is PALM for photo-activated localization microscopy. Betzig likes to compare the perfrmance of PALM and different other high-resolution microscopy techniques that are applicable for biology. The technique that he highlights most is structured illumination microscopy (SIM)[4].

Finally Betzig shows how laterally illuminated light sheet microscopy has recently further shifted the practical resolution limit and how he and his colleagues are continuing working on this technique in his group at Janelia Farm.


  1. E. Betzig, "Proposed method for molecular optical imaging", Optics Letters, vol. 20, pp. 237, 1995.
  2. G.H. Patterson, "A Photoactivatable GFP for Selective Photolabeling of Proteins and Cells", Science, vol. 297, pp. 1873-1877, 2002.
  3. E. Betzig, G.H. Patterson, R. Sougrat, O.W. Lindwasser, S. Olenych, J.S. Bonifacino, M.W. Davidson, J. Lippincott-Schwartz, and H.F. Hess, "Imaging Intracellular Fluorescent Proteins at Nanometer Resolution", Science, vol. 313, pp. 1642-1645, 2006.
  4. B. Bailey, D.L. Farkas, D.L. Taylor, and F. Lanni, "Enhancement of axial resolution in fluorescence microscopy by standing-wave excitation", Nature, vol. 366, pp. 44-48, 1993.

William E. Moerner on fluorescence-based super-resolution microscopy

The second Nobel laureate’s talk at the CLEO plenary session today. William E. Moerner from Stanford University now explains how he and his colleagues discovered the nowadays highest resolution microscopy techniques. Different to Stefan Hell, he focuses on single molecule based microscopy, including the effects of blinking and photo bleaching. How does that work?

It is about active control. If all molecules emit light at the same time, their point spread functions would overlap in an image, making them indistinguishable. Now, if they emitted light not at the same time, but sequentially, their PSFs would not be indistinguishable. Is that possible? It is, if you are able to switch on and off your molecules. This is a kind of time multiplexing. This was demonstrated in 1997 and allowed for an enormous increase in microscopic resolution[1].

Today’s challenges? It seems clear that the key to the method is the fluorescent molecules. Therefore identifying and applying new, different fluorescent molecules is the limiting factor for applications in imaging different new biology applications.

Also, applying the techniques to 3D optical tomographic applications in biology recently lead to new important breakthroughs[2].



  1. R.M. Dickson, A.B. Cubitt, R.Y. Tsien, and W.E. Moerner, "On/off blinking and switching behaviour of single molecules of green fluorescent protein", Nature, vol. 388, pp. 355-358, 1997.
  2. M.K. Lee, P. Rai, J. Williams, R.J. Twieg, and W.E. Moerner, "Small-Molecule Labeling of Live Cell Surfaces for Three-Dimensional Super-Resolution Microscopy", Journal of the American Chemical Society, vol. 136, pp. 14003-14006, 2014.

The optics and photonics community gathering in San Jose: CLEO

CLEO conference in San Jose, California.

CLEO conference in San Jose, California.

Today one of the largest and, in my personal view, most concise and exciting optics and photonics conference, the annual CLEO conference has started in San Jose, California. Just now, after a day full of novel nanophotonics sessions, I am attending the first of a couple of plenary talks.

Tony Heinz from Stanford University has started with a talk on 2D optical materials, particularly graphene and its extraordinary properties regarding confinement, fundamental physics involved with its single-atomic thickness and its potentially low-loss future properties.

Now, the first of 6 recent Nobel laureates in the field of optics, Stefan Hell, is starting his talk on unprecedentedly high resolution microscopic imaging techniques. He explains how he and his colleagues beat the good old Abbe diffraction limit that originally restricted the maximum resolution of light microscopes to the iconic formula of the Abbe diffraction limit. STED: Stimulated emission depletion microscopy.

Cui et al.: Hybrid Plasmonic Photonic Crystal Cavity for Enhancing Emission from near-Surface Nitrogen Vacancy Centers in Diamond

TOC GraphicShanying Cui, Xingyu Zhang, Tsung-li Liu, Jonathan Lee, David Bracher, Kenichi Ohno, David Awschalom, and Evelyn L. Hu in ACS Photonics
Abstract: Optical cavities create regions of high field intensity, which can be used for selective spectral enhancement of emitters such as the nitrogen vacancy center (NV) in diamond. This report discusses a hybrid metal–diamond photonic crystal cavity, which provides greater localization of the electric field than dielectric cavities and mitigates metal-related losses in existing plasmonic structures. We fabricated such hybrid structures using silver and single-crystal diamond and observed emission enhancement of NVs near the diamond surface. We measured a mode quality factor (Q) as high as 170 with a simulated mode volume of ∼0.1 (λ/n)3 and demonstrated its tunability. This cavity design and the associated fabrication approach specifically target enhancement of emission from near-surface NVs.

Go to the original article…


  1. S. Cui, X. Zhang, T. Liu, J. Lee, D. Bracher, K. Ohno, D. Awschalom, and E.L. Hu, "Hybrid Plasmonic Photonic Crystal Cavity for Enhancing Emission from near-Surface Nitrogen Vacancy Centers in Diamond", ACS Photonics, vol. 2, pp. 465-469, 2015.

Douglas et al.: Quantum many-body models with cold atoms coupled to photonic crystals

J. S. Douglas, H. Habibian, C.-L. Hung, A. V. Gorshkov, H. J. Kimble, and D. E. Chang in Nature Photonics [1]

Go to the original article…


  1. J.S. Douglas, H. Habibian, C. Hung, A.V. Gorshkov, H.J. Kimble, and D.E. Chang, "Quantum many-body models with cold atoms coupled to photonic crystals", Nature Photonics, vol. 9, pp. 326-331, 2015.

Piazza et al.: Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field

L Piazza, T.T.A. Lummen, E Quiñonez, Y Murooka, B.W. Reed, B Barwick, and F Carbone in Nature Communications [1]

Abstract: Surface plasmon polaritons can confine electromagnetic fields in subwavelength spaces and are of interest for photonics, optical data storage devices and biosensing applications. In analogy to photons, they exhibit wave–particle duality, whose different aspects have recently been observed in separate tailored experiments. Here we demonstrate the ability of ultrafast transmission electron microscopy to simultaneously image both the spatial interference and the quantization of such confined plasmonic fields. Our experiments are accomplished by spatiotemporally overlapping electron and light pulses on a single nanowire suspended on a graphene film. The resulting energy exchange between single electrons and the quanta of the photoinduced near-field is imaged synchronously with its spatial interference pattern. This methodology enables the control and visualization of plasmonic fields at the nanoscale, providing a promising tool for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits.


  1. L. Piazza, T. Lummen, E. Quiñonez, Y. Murooka, B. Reed, B. Barwick, and F. Carbone, "Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field", Nature Communications, vol. 6, pp. 6407, 2015.

Millen et al.: Cavity Cooling a Single Charged Levitated Nanosphere

J. Millen, P. Z. G. Fonseca, T. Mavrogordatos, T. S. Monteiro, and P. F. Barker in Physical Review Letters[1]
Abstract: Combining two trapping techniques reduces the motion of a levitated bead close to the point where quantum effects should become observable.

Go to the original article…


  1. J. Millen, P. Fonseca, T. Mavrogordatos, T. Monteiro, and P. Barker, "Cavity Cooling a Single Charged Levitated Nanosphere", Physical Review Letters, vol. 114, 2015.

Selected optics landmark papers in PRL – for free

International year of lightA lot of groundbreaking optics research throughout the last decades has been published in Physical Review Letters and before in its practical predecessor Physical Reviews. To celebrate the international year of light 2015 PRL has decided to compile some selected important papers and make them free to read for everyone. Remember, PRL is still one of those ‘good old’ non-open-access journals. The list is online here and in a shorter version. Also, over the year Physics is publishing highlight articles on many of those discoveries that are linked from the overview site.