Confocal surface plasmon microscopy with vortex beam illumination for biosensing application

Abstract

We have developed surface plasmon interferometric microscope and demonstrated that by integrating a phase spatial light modulator (SLM) on conjugate back focal plane of confocal microscope objective lens, this enables us to perform surface plasmon phase imaging and phase sensing using phase stepping interferometry over well confined region [1-6]. In this paper, we address one of the key limitations of the system, which is data acquisition time. Since phase stepping algorithm requires 3 (for 120 degrees step) to 4 (for 90 degrees step) phases in order to obtain a relative phase value between the reference beam and the signal beam the phase pattern on the SLM needs to be frequently updated and the liquid crystal takes time to respond. This slows down the data acquisition process. Moreover, acquiring the phase steps at different times increases microphonic noise and introduces artefacts into real time experiments, such as protein binding. In this paper, we show that a simple and innovative method to overcome these issues is to employ a vortex reference beam provided by 0 to 2π rad topological phase pattern on the SLM; this enables us to obtain multiple phase information in one single shot measurement without updating the SLM pattern.