Index-of-refraction sensors: virtually unlimited sensing power at the critical angle

Abstract

In an effort to improve and simplify refractive index sensors, we identified a basic operation mode at the critical angle. Sensitivity to the refractive index is higher than in standard surface plasmon resonance sensors, and we have been able to demonstrate analytically that it is virtually an unbounded value. We describe this approach and submit a complete analytical study demonstrating its unlimited sensing power. To test the approach, we constructed an economical and basic sensor. Despite its simplicity, we demonstrated the discrimination capability to be of the order of 10(-6), as far as we know close to the best sensitivity ever recorded. This detection method is generally applicable to any optical system and may pave the way for the next generation of optical sensing devices.

A local curve-fitting method for the complex refractive index measurement of turbid media

“…This fitting rewrites equation (1) as where a width ε of the local range is set as full-width at half-maximum (FWHM) of the peak on the angular gradient curve of τ . The characteristic of the reflectivity around the critical angle θ c has previously been exploited for the refractive index measurement of high sensitivity [11,12], but operating at only one data point slightly below θ c would not be as robust as the fitting with multiple points. For the measured and theoretical curve, the transmission ratios τ and τ in tworeflection DDCAR are substituted for reflectivities R and R. τ is a function of R shown in equation ( 3), and it has been given in [10]…”