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

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.

Quantitative Cross-Platform Performance Comparison between Different Detection Mechanisms in Surface Plasmon Sensors for Voltage Sensing

“…Firstly, let us consider the uniform gold sensor as shown in Figure 3 as a basis to compare the other types of structures. Figure 7 a shows reflectance responses of the p-polarized incident light at 632.8 nm (HeNe laser wavelength) incident wavelength when the total gold thickness was varied from 20 nm to 80 nm and the applied potential was of 0 V. The total gold thickness that gave the minimum reflectance dip was 47 nm, which was in the range of optimum gold thickness for SPR sensor [ 15 ]. This 47 nm gold sensor was then calculated for different applied voltage levels as shown in Figure 7 b.…”

“…In this section, we consider only the thin film bimetallic structure as shown in Figure 4 . The thin film is applicable for in vitro SPR microscopic sensing [ 15 , 21 , 22 , 23 , 24 ]. Here, the gold layer was in contact with the 0.15 M NaCl electrolytic solution, since the gold is chemically stable and inactive [ 25 , 26 ] whereas silver is highly reactive and can also form hazardous substances [ 27 ], such as, silver sulfide Ag 2 S. The thicknesses of the silver and gold layers considered in this paper were at least 15 nm thick due to two major reasons.…”

“…It is important to point out that if the sensitivity or how far the plasmonic dip moves is more important than the depth of the SPR dip. This is the case for the confocal surface plasmon microscopy system [ 15 , 21 , 22 ] and SPR phase measurements [ 13 , 31 ]. It is then better to operate at slightly higher reflectance intensity as labelled in ‘E’ in Figure 12 a.…”

“…Recently, there has been an interest in employing label-free detection using surface plasmon resonance (SPR) as a voltage sensing platform for biological samples [ 15 , 16 , 17 , 18 , 19 ]. The SPR has been a gold standard for real-time binding kinetics studies [ 20 ] and very low concentration biological measurements [ 21 ].…”

Analysis of Open Grating-Based Fabry–Pérot Resonance Structures With Potential Applications for Ultrasensitive Refractive Index Sensing

“…A resonant cavity using Bragg reflectors [2], as shown in Fig. 1(c) can have even better performance with a sharper response since the ohmic losses are significantly reduced [3]. In these types of closed resonator structures, the analyte becomes an integral part of the resonant structure, which means that it is possible to have a very large change in the resonant position while retaining the sharp response.…”