A surface wave has to not only satisfy the laws of electromagnetics in two distinct mediums but also boundary conditions. Hence, the propagation of a surface wave is easily disturbed by a change of constitution of either of the two partnering mediums.
This renders surface-wave propagation attractive for optical sensing of stimuli such as infiltrant matter, quasistatic magnetic fields, and temperature changes.
Among surface waves of different categories, the surface plasmon-polariton (SPP) wave guided by a metal/dielectric interface is extensively used for optical sensing. During the 1980s, another surface wave was theoretically predicted. It came to be called the Dyakonov wave.
Its propagation is guided by the interface of two homogeneous dielectric materials of which at least one must be anisotropic. As dissipation in both partnering mediums is extremely small, the Dyakonov wave should propagate over very long distances. It should also be excitable using the prism-coupled configuration commonly used to excite SPP waves.
The Dyakonov wave can propagate only in a very restricted range of directions along the interface. The angular existence domain rarely exceeds a degree in width, which seriously impeded experimental verification of the existence of the wave. Only in 2009 was it actually observed.
A schematic setup under study consists of a semi-infi nite Ag-GaAs superlattice (x>0) and an isotropic cover (x<0), either N-BAK1 or P-SF68
Now Juan Miret et al. have theoretically shown a way to widen the angular existence domain to several tens of degrees in their paper entitled, “Substantial enlargement of angular existence range for Dyakonov-like surface waves at semi-infinite metal-dielectric superlattice,” published in the Journal of Nanophotonics in November 2012.
The widening is achievable by replacing the anisotropic partnering medium by a metal-dielectric superlattice with the volume fraction of the metal not exceeding 0.1. The superlattice is periodic in a direction lying wholly in the interface plane.
The incorporation of a metal in one of the partnering mediums would naturally reduce the propagation length, but the widening of the angular existence domain may compensate by making these surface waves robust for optical sensing applications.
A new avenue for experimental research beckons SPIE members and other researchers.
Coauthors in the research are Carlos J. Zapata-Rodriguez, Zoran Jakšic´, Slobodan Vukovic´, and Milivoj R. Belic´.
Source:Journal of Nanophotonics6, 063525 (2012); doi:10.1117/1.JNP.6.063525.
– Akhlesh Lakhtakia is editor of the Journal of Nanophotonics.
Light-emitting nanoprobes detect tumors
A group of Taiwan researchers has reported that zinc oxide (ZnO) nanorods bonded to antibodies may be useful as nanoprobes for sensing cancer cells during tumor resection.
SPIE member Yung-Tsan Chen et al. presented “ZnO light-emitting nanoprobes for tumor detection” at the Nanoscale Imaging, Sensing, and Actuation for Biomedical Applications conference at BiOS in February.
The researchers say the detection of purple light from epidermal growth factor receptor (EGFR) cells connected to ZnO nanorods may make real-time identification of cancer cells during surgery easier than with the traditional fluorescence methods. The cancer cells can be excised more precisely with the help of purple light emission, they added.
Their paper can be found in the SPIE Digital Library at: http://dx.doi.org/10.1117/12.2004511
Special journal sections focus on nano-bio
Papers related to the February 2013 SPIE conference on Nano-Bio Sensing, Imaging, & Spectroscopy are being solicited for special sections in two photonics journals.
The Journal of Nanophotonics is seeking manuscripts by 1 June for a special section on nanobiophotonics and related techniques based on the conference in South Korea. This special section is devoted to advances in the techniques and theory of nanobiosensing, nanobioimaging, and nanobiospectroscopy.
The call for papers is open to anyone who wishes to submit a relevant paper, even those who did not attend the conference.
Guest editor is SPIE member Mun Seok Jeong of the Gwangju Institute of Science and Technology (South Korea).
Other papers related to the NBSIS conference are expected to be published in a special section of the Journal of Biomedical Optics.
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