Characterization of light collection through a subwavelength aperture from a point source
We experimentally measure and theoretically model the light transmission characteristics of subwavelength apertures. The characterization consists of translating a point source at varying vertical height and lateral displacement from the aperture and measuring the resulting transmission. We define the variation of the transmission with lateral source displacement as the collection mode point spread function (CPSF). This transmission geometry is particularly relevant to subwavelength aperture based imaging devices and enables determination of their resolution. This study shows that the achieved resolutions degrade as a function of sample height and that the behavior of sensor devices based on the use of apertures for detection is different from those devices where the apertures are used as light sources. In addition, we find that the measured CPSF is dependent on the collection numerical aperture (NA). Finally, we establish that resolution beyond the diffraction limit for a nominal optical wavelength of 650 nm and nominal medium refractive index of 1.5 is achievable with subwavelength aperture based devices when the aperture size is smaller than 225 nm.
Additional Information© 2006 Optical Society of America Original Manuscript: August 22, 2006. Manuscript Accepted: October 20, 2006. Revised Manuscript: October 18, 2006. Published: October 30, 2006 We thank Zhenyu Li, Jaewoo Choi and James Adleman from Caltech, Dr. David Erickson from Cornell University, and Liang Feng from UCSD for helpful discussions. We are grateful to Dr. Scherer's group at Caltech and UCLA's Nanolab for their assistance in fabrication. We thank Caltech's Molecular Materials Resource Center for providing us with the NSOM system. This work was funded by DARPA Center for Optofluidic Integration (California Institute of Technology).
Published - HENoe06.pdf