Widefield Confocal Microscope for Surface Wave K-Vector Measurement

Abstract

Optical surface waves are guided light on surface of optical structures. There are several optical structures that support optical surface waves, such as, nanostructures, gratings, optical waveguides and metamaterials. Optical surface waves have proven themselves very promising candidates for several applications including, biosensing, optical computing and optical circuitry. The characteristics of surface wave can be characterised by the wave vector (k-vector) of the surface wave. In this paper, we will discuss how a modified confocal microscope integrated with a phase spatial light modulator allows us to measure both the real part and the imaginary part (attenuation coefficient) of the surface wave k-vector. Surface plasmon resonance (SPR) excited on a uniform gold surface through Kretschmann configuration is employed as an example in this talk. Note that the system is not limited to the SPR. It is also applicable to other types of optical surface waves. We have demonstrated in our recent publication that the modified confocal not only provides the k-vector measurement both real and imaginary, it also allows us to separate different loss mechanisms in SPR. One limitation of the system was the single point detection. Here we will discuss the current stage of our development in widefield confocal surface plasmon microscope, which allows us to measure multiple points simultaneously. This has been achieved by integrating another amplitude spatial light modulator in the image plane of the objective lens. Use of orthogonal illumination patterns allows the image plane to be sequentially amplitude modulated and post-processed to recover the confocal image.