Title : Single-scattering theory of light diffraction by a circular subwavelength aperture in a finitely conducting screen
Authors : Evgeny Popov, Michel Nevière, Anne Sentenac, Nicolas Bonod, Anne-Laure Fehrembach, Jérome Wenger, Pierre-François Lenne, and Hervé Rigneault
It has been released in the February edition of the journal of the optical society of JOSA A, vol. 24, pp. 339-358 (2007). Click here to read the abstract and download the paper (subscribers only).
This theoretical paper provides analytical formulas for the electromagnetic field diffracted by a subwavelength aperture in an opaque screen (metallic or dielectric). My contribution to these findings is very small, my name was put on the paper mostly because of the ongoing collaboration between the theoretical and experimental groups at the Fresnel Institute.In my opinion, the main application concerns the far-field directivity from a nanoaperture (part 6, figures 8 to 11). The theory predicts a directivity of the radiation pattern that increases for small permittivities. Surprisingly, this holds for metals AND dielectrics, thus independently of surface plasmon excitation.
Aaaarrrrgggghhhhh…. I finally submitted that doomed paper to this high-impact factor physics journal. Took me a too long time to write it down, and to get it into the limited article length :o((
For those interested, here is the abstract :
As member of the OMNT “materials and components for optics” committee, I regularly give a selection and a brief description of articles, that I found particularly relevant to the field. Here is my latest selection :
"Creating hot nanoparticle pairs for surface enhanced Raman spectroscopy through optical manipulation"; Fredrik Svedberg, Zhipeng Li, Hongxing Xu, Mikael Käll, Nano Letters 6, 2639-2641 (2006).
Abstract : We use optical tweezers to move single silver nanoparticles into near-field contact with immobilized particles, forming isolated surfaceenhanced Raman spectroscopy (SERS) active Ag particle dimers. The surface-averaged SERS intensity increases by a factor 20 upon dimerization. Electrodynamics calculations indicate that the final approach between the particles is due to “optical binding”. The described methodology may facilitate controlled single molecule SERS analysis.
"Enhancing sensitivity of a whispering gallery mode biosensor by subwavelength confinement"; O. Gaathon, J. Cullic-Viskota, M. Mihnev, I. Terakoa, S. Arnold, Applied Physics Letters 89, 223901 (2006).
Abstract : the authors demonstrate enhanced sensitivity of a spherical whispering gallery mode biosensor WGMB by confining orbiting light near the surface using a subwavelength high refractive index layer on a fluorine doped silica microsphere. Their experiments at a free space wavelength of 1310 nm show that the frequency shift sensitivity by changing the external refractive index is increased by more than 700% by adding a 340 nm thick polystyrene layer. This advance is expected to move the WGMB well into the lead as the most sensitive method for unlabeled biosensing.
"Shining new light on neural circuits"; Greg Miller, Science 314, 1674-1676 (2006).
Abstract : Emerging methods that combine genetics and optics have neuroscientists glowing about the possibilities
A point that is always missed by readers of peer-reviewed articles is the discussion with referees, which I believe often contains interesting comments and should somehow be available to the scientific community. To (locally) correct for this, I give here the reviewers’ remarks concerning our latest Optics Express publication on FCCS.
“[…] The experiments are carefully done, the analysis seems correct, the FCS and FCCS experiments are internally consistent and the results are very convincing. […] This is a straightforward next step of earlier work of the group of Wenger, using nano apertures, which looks very promising and widens the path for the use of FCCS. “
“[…] It is an important work on the field of fluorescence microscopy and is worth publishing in Optics Express. Unfortunately, the manuscript is not written in a well manner. […] If it wasn't for this important topic and the in principle well-done experimental work, I would not recommend this work for publication.”
I obviously do not share his global opinion ! Reviewer #2 then wrote a list of 20 points, which I cannot detail here. Fortunately, my answers and corrections were convincing. I give here a selection of the main discussion :
Q: “How is the influence of the nanoholes on the performance of biological assays in general? Usually, biological and chemical reactions are influenced by a mechanically confined sample volume.”
A: Actually, we don’t know much about this issue, which is well beyond the scope of this paper. We can only say that we never detected any effect of the aperture on the reactions we tested. A nice point with Al is the aluminum oxide layer that forms naturally on top of the film and passivates the surface. Thus we have no reason to think that the aperture has a large influence on the biochemical reactions. A challenging question is to determine by how much the nanoaperture itself affects the molecular diffusion. We are aware of some work preformed by Harold Craighead’s group (Samiee et al, Biophys. J. 88, 2145), but this reference assumes a 1D diffusion. If this seems valid for a 50nm diameter aperture, we question the fact that it still holds for a 340nm diameter hole, which is obviously more complex. We use the general FCS formula for a 3D Brownian diffusion, while letting the aspect ratio s vary freely. The numerical fits converge easily, and remarkably account for the experimental data.