“Nanooptics and nanophotonics”

Thermal influence from the absorption of optical flux on the indications of the sensor "prism - gold nanolayer - water"
A.D. Suprun, L.V. Shmeleva
 Department of Theoretical Physics, Faculty of Physics, Taras Shevchenko National University of Kyiv. Volodymyrska Street, 64/13, Kyiv-01601, Ukraine. 
E-mail: lshmel@univ.kiev.ua  

In previous our studies, the thermal effect of laser radiation on the sensory effect of the three-layer structure "prism - gold - water" was analyzed. The presence of water in this structure is due to the fact that in many of these sensors, water is one of the components of the analyte. This is especially true for biosensors. In addition, for water, the dependence of the refractive index on temperature and wavelength in practically significant ranges (0÷100ºС and 300÷1000 nm, respectively) is well studied.
It is known that the influence of a laser radiation flux on a metal nano layer can lead to its heating and to the same heating of nearby water layers. In previous investigations, the approximation of an infinite absorption coefficient of the gold layer was considered. This approximation showed a significant influence on the thermal effect of radiation on the sensor indications. But the infinite absorption coefficient model significantly levels the specifics of gold. Such a model does not difference metals by their absorption coefficient.
In this research, the finiteness of the absorption coefficient for gold and the influence of this circumstance on the heating of the gold nanolayer were taken into account. It was found that as the absorption coefficient decreases in the sense of the inequality k < ∞, the amount of radiation flow, required to reach the same temperature as for k = ∞, increases. This means, in particular, that taking into account the finiteness of the absorption coefficient makes it possible to significantly expand the range of measuring the flux for the sensory effect.
The range of radiation flux at which the effect of temperature on the sensory effect can be neglected also increases. The magnitude of the sensory effect itself also increases both in terms of the wavelength and in terms of the resonant angle of incidence.