Characterization of light collection through a subwavelength aperture from a point source

Xin Heng,Xiquan Cui,David W Knapp,Changhuei Yang,Demetri Psaltis,Emily J Mcdowell,Jigang Wu,Zahid Yaqoob

doi:10.1364/oe.14.010410

Abstract

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.

Highlights

IntroductionThe unique transmission and diffraction properties of a subwavelength circular aperture [1], a single nanoaperture with designed shapes [2, 3], a single nanoaperture surrounded by corrugated surface [4] or a tightly-spaced nanoaperture array [5, 6] have all been studied and reported in the recent past
Subwavelength apertures are known to possess interesting characteristics
As the collection mode point spread function (CPSF) are narrowest when H is small, we can conclude that a type-II aperture based imaging devices (ABIDs) should provide highest possible resolution when the target sample is at close proximity to the aperture

Summary

Introduction

The unique transmission and diffraction properties of a subwavelength circular aperture [1], a single nanoaperture with designed shapes [2, 3], a single nanoaperture surrounded by corrugated surface [4] or a tightly-spaced nanoaperture array [5, 6] have all been studied and reported in the recent past. Subwavelength aperture based imaging devices (ABIDs) have the potential to deliver resolution that is beyond the diffraction limit; the resolution of such devices is fundamentally limited by the aperture size. These devices have the distinct advantage of enabling compact and portable analysis systems. ABID compares favorably with imaging systems based on other optical imaging strategies, such as laser scanning confocal microscopy [15], structured illumination [16] and stimulated emission depletion microscopy [17]

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