Application of confocal surface wave microscope to self-calibrated attenuation coefficient measurement by Goos-H\xe4nchen phase shift modulation

Suejit Pechprasarn,Terry W K Chow,Michael G Somekh

doi:10.1038/s41598-018-26424-2

Suejit Pechprasarn, Terry W K Chow + Show 1 more

Open Access

https://doi.org/10.1038/s41598-018-26424-2

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Abstract

In this paper, we present a direct method to measure surface wave attenuation arising from both ohmic and coupling losses using our recently developed phase spatial light modulator (phase-SLM) based confocal surface plasmon microscope. The measurement is carried out in the far-field using a phase-SLM to impose an artificial surface wave phase profile in the back focal plane (BFP) of a microscope objective. In other words, we effectively provide an artificially engineered backward surface wave by modulating the Goos Hänchen (GH) phase shift of the surface wave. Such waves with opposing phase and group velocities are well known in acoustics and electromagnetic metamaterials but usually require structured or layered surfaces, here the effective wave is produced externally in the microscope illumination path. Key features of the technique developed here are that it (i) is self-calibrating and (ii) can distinguish between attenuation arising from ohmic loss (k″Ω) and coupling (reradiation) loss (k″c). This latter feature has not been achieved with existing methods. In addition to providing a unique measurement the measurement occurs of over a localized region of a few microns. The results were then validated against the surface plasmons (SP) dip measurement in the BFP and a theoretical model based on a simplified Green’s function.

Highlights

Optical surface waves occur when light is guided by a surface; these waves propagate parallel to the surface with its energy confined close to that surface
This paper has demonstrated how a modified confocal microscope can be used to measure attenuation of surface waves over a localized region
The main result of the paper, is to show how the system can be used to measure attenuation coefficients associated with different loss mechanisms as a direct far-field method and without reference to any model

Summary

Introduction

Optical surface waves occur when light is guided by a surface; these waves propagate parallel to the surface with its energy confined close to that surface. The method presented can be regarded as a bridge between near field methods and low spatial resolution far field measurements Another approach involves indirect evaluation of the parameters by using a model to fit to the loss parameters. There are a number of publications developing theoretical models to explain the relationship between the amplitude and phase of the SP reflection spectrum and its attenuation including Goos-Hänchen phase shift model[14], pole and zeros model[15], Poynting vector[16], multilayered structure model[17,18] and a simplified Green’s function[19,20] All these methods involve fitting to a model which require detailed knowledge of the structure, clearly our direct measurement measures the generated waves without any presumptions about the structure

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Results

Conclusion