I’ve joined a group of folks on Twitter who have vowed to read roughly a paper a day for an entire year, and will summarize my reading here occasionally. Part 1 can be read here, part 2 can be read here, and part 3 can be read here. Links are provided for those with university access who are interested in reading more. These posts are a bit more technical than my usual fare, so feel free to ignore if you’re not an optics enthusiast! More fun stuff to come soon.

2/23: Circularly symmetric operation of a concentric‐circle‐grating, surface‐ emitting, AlGaAs/GaAs quantum‐well semiconductor laser, T. Erdogan, O. King, G.W. Wicks, D.G. Hall, E.H. Anderson and M.J. Rooks (1992). I’ve been reading a lot about “vector beams” these past few weeks, in which the polarization of light either points radially from the center of the beam or circulates azimuthally around it. This paper, which describes a new laser design with azimuthal polarized light, sparked the modern interest in such beams.

2/24: Focusing of high numerical aperture cylindrical vector beams, K.S. Youngworth and T.G. Brown (2000). So what good are “vector beams,” that possess unusual polarization? This paper, combining theory and experiment, noted how radial beams produce a strong longitudinal electric field at focus, which can be used to accelerate charged particles.

2/25: The electric and magnetic polarization singularities of paraxial waves, M.V. Berry (2004). I’ve been extensively studying the “polarization singularities” of light for my chapter on the subject in my singular optics book. Basically, points in a field where light is circularly polarized may be considered “singular” and distinct from other points. This paper is one in a long set of articles studying the properties of such singularities.

2/26: An image of an exoplanet separated by two diffraction beamwidths from a star, E. Serabyn, D. Mawet and R. Burruss (2010). In order to actually image planets around distant stars, it is necessary to block out the starlight and only image the light of the planet itself, which can be a million times dimmer. A simple strategy is to just put a physical obstruction in the center of the imaging system to block out the star, but light can diffract around this obstruction. It is also possible to use a vortex mask, however, to almost perfectly block out the star’s light! This paper was one of the first practical demonstrations of such a vortex “coronagraph.”

2/27: Optical lattice model towards nonreciprocal invisibility cloaking, T. Amemiya, M. Taki, T. Kanazawa, T. Hiratani and S. Arai (2015). This recent paper proposes a quite unique method to make invisibility “nonreciprocal,” meaning that the cloaked person cannot be seen but can nevertheless see him/herself. The strategy involves something I don’t quite understand yet, the idea of creating an effective “magnetic field for photons.” Light particles, being uncharged, are not influenced by a magnetic field, but it is possible to make materials that act as an effective magnetic field for light.

2/28: Nodal areas in coherent beams, G.J. Ruane, G.A. Swartzlander, Jr., S. Slussarenko, L. Marrucci, and M.R. Dennis (2015). Typically, zeros in a light wave manifest as lines in three-dimensional space, around which the field swirls, making an optical vortex. However, it is possible to design fields that are zero over an extended surface in three-dimensional space, but it has not been explored in detail before. Such “nodal areas” were the subject of this paper.

3/1: Perfect vortex beam: Fourier transform of a Bessel beam, P. Vaity and L. Rusch (2015). Beams with optical vortices are of potential use in applications like free-space optical communications, but one major problem is that different orders of vortex beams spread at different rates on propagation. A “perfect” vortex beam would have the same spreading properties for any order, and this paper suggests one method for making a perfect beam.

3/2: Vortex Hermite-Gaussian laser beams, V.V. Kotlyar, A.A. Kovalev, and A.P. Porfirev (2015). There are two important classes of laser beams that are in general use: Laguerre-Gauss beams, which possess vortices, and Hermite-Gauss beams, which do not. This article describes a method to generate beams with both properties.

3/3: Supersymmetric transparent optical intersections, S. Longhi (2015). Data is transmitted over much of the internet using light transmitted through fiber optic cables. However, though it could be useful to design intersections in such optical waveguides, light is typically lost in the crossing. In this paper, a new lossless design for intersections is introduced using supersymmetry, which I’ve blogged about before.

3/4: Transient behavior of invisibility cloaks for diffusive light propagation, R. Schittny, A. Niemeyer, M. Kadic, T. Bückmann, A. Naber, and M. Wegener (2015). A major problem with most invisibility cloak designs is that they are very wavelength-specific: that is, they might work for a certain shade of red but not blue or green. In a diffusive medium, where light bounces around strongly like a ball in a pinball machine, it is possible to make broadband cloaks, however. Here, the authors study the transient behavior of these cloaks: do they still work when the illumination is switched on suddenly, or only when the light has been on for some time?

3/5: New Green-function formalism for surface optics, J.E. Sipe (1987). A “Green’s function” is a function that can be used to describe the behavior of light emitted from a point source, and is a valuable mathematical tool in optics and other fields. In this paper, Green’s functions are applied to the study of light interacting with an interface between two media.

3/6: Polarization singularities in the clear sky, M.V. Berry, M.R. Dennis and R.L. Lee Jr. (2004). This is a cool paper that looks at the structure of the earlier-mentioned polarization singularities in the sky! It turns out that there are four polarization singularities: two near the Sun and two near the “anti-Sun” on the opposite side of the sky, though only one of the latter two can be seen above the horizon.

3/7: Discrete-dipole approximation for scattering calculations, B.T. Draine and P.J. Flatau (1994). Calculating how light scatters off of a complicated object is a difficult problem that cannot be solved analytically — with pen and paper — in all but the simplest cases. The discrete-dipole approximation is an early numerical technique where a scattering object is approximated as a collection of point dipoles. This review article summarizes the technique.

3/8: Measuring the transverse spin density of light, M. Neugebauer, T. Bauer, A. Aiello, and P. Banzer (2015). I’ve talked about circularly polarized light, where the electric field traces out a circle in a plane transverse to the direction of propagation. But what happens when the electric field circulates kind of like a bicycle wheel, “rolling” in the direction of propagation? It’s not terribly easy to measure, but that’s just what this paper did.

3/9: A proof of the hairy ball theorem, M. Eisenberg and R. Guy (1979). I’ve blogged about the hairy ball theorem before, which states that it is impossible to comb a hairy ball flat without leaving a cowlick somewhere on the ball. Well, it turns out that it would be very useful to include a detailed explanation of the theorem in my book, so I’m hunting for a simple proof, if such a thing exists.

3/10: Poynting singularities in optical dynamic systems, A.V. Novitsky and L.M. Barkovsky (2009). The power flow of light, referred to as the Poynting vector, also exhibits “singularities,” points where the energy goes around in circles. In this paper, these Poynting singularities are classified using the familiar mathematics of dynamic systems theory.

3/11: Remarks on forces and the energy-momentum tensor in macroscopic electrodynamics, V.L. Ginzburg and V.A. Ugarov (1976). I’ve also blogged about the Abraham-Minkowski controversy before, in which there is a vigorous and unsolved debate over whether the momentum of light increases or decreases when entering a transparent medium. This is something else I want to write about in my book, but detailed derivations of the related math are hard to come by. This paper is one that includes some detail.

3/12: The hairy ball theorem via Sperner’s lemma, T. Jarvis and J. Tanton (2004). Another proof of the hairy ball theorem. Still looking for a proof I can use in my book!

3/13: Transverse energy flows in vectorial fields of paraxial beams with singularities, A.Ya. Bekshaev and M.S. Soskin (2007). Finally, here’s one more paper on Poynting singularities, which also uses the dynamic systems classification but more details.

That’s it for a couple weeks of #365papers!