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bulletRodney Agayan

Rodney Agayan
(Applied Physics Graduate Student)
http://www-personal.umich.edu/~ragayan/
ragayan@umich.edu

Background:
Prior to attending the University of Michigan, I acquired a BS in Applied & Engineering Physics at Cornell University.  My senior-level research involved the fabrication of gratings and fresnel lenses via microcontact printing and pattern transfer to self-assembled monolayers on Au surfaces.  I also did research at the Lawrence Livermore National Laboratory for a total of two years.  I spent about five months in the Inertial Confinement Fusion department learning how to fabricate extremely efficient dielectric gratings using holographic interference lithography.  The remainder of my time at Livermore was spent utilizing the same interometric lithography technique to design holographic bifocal contact lenses.

Current Research:
As a student in Applied Physics, I spent much of my first couple years in the Kopelman group exploring several fields, the gamut of which extends from chemistry to biophysics to optics.  While most of this ongoing "exploration" consists of reading journal publications, juggling coursework, and lots of speculation, I've also managed to do some experimental labwork.

In general, I would like to study the interaction between light and matter, with some specification to biological material.  Such an endeavor requires an interdisciplinary approach comprised of a wide variety of scientific fields.  Thus, I am also interested in such aspects as non-linear and ultrafast spectroscopy, near-field optics, quantum optics and single-molecule studies.

My primary interest lies in the field of optics and its application to the study of biological media. Most recent experiments have investigated the phenomenon of trapping dispersive materials in an optical potential well formed by a focussed laser beam. Such contraptions, also known as "optical tweezers", are widely used to realize and/or study, for example, motional characteristics of cellular structures, mechanical properties of DNA, or the manipulation of micro- and nano-scale probes.  In particular, I have been looking at the possibility of enhancing tweezer forces by trapping absorptive particles near resonance.  Although the principal motive of this study is to enable the intracellular manipulation of PEBBLEs (sol gel and polymeric), there is great interest in other particle types, including solid state crystals and semiconductor nanostructures.

NEAR RESONANCE TRAPPING

Research in the Kopelman laboratory involves the creation of nano-scale biochemical probes for sensing analyte concentrations within and around cells. A smaller probe offers the advantages of non-invasiveness, spatial resolution, response speed and lower absolute detection limit. In order to manipulate this smaller probe optically (i.e. with laser tweezers) for measurements in and around single cells, one must specifically trap the particle without perturbing the surrounding environment. To achieve this specificity, we proposed near-resonance trapping of absorptive particles.

The Classical Electron Oscillator(CEO) model provides a simple description of the frequency-dependent complex polarizability of a Rayleigh particle (d << lambda) in a focused laser beam. Real and imaginary parts of the polarizability are proportional to the gradient and scattering forces, respectively. Similar relations occur for components of the complex index of refraction in the geometrical optics regime (d >> lambda). By frequency tuning the trapping beam near the probe's absorption resonance, one can maximize the gradient force and minimize the scattering force, thus optimizing the single beam gradient trap.

For more details on the theoretical aspects please refer to the following publications:

Reference in Phys. Rev Focus

Applied Optics-LP, Volume 41, Issue 12, 2318-2327.

 


 

 

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