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Device for the measurement of refractive index of liquids on the base of surface plasmon resonance

№39 Department of Optoelectronics polariton
N.L. Dmitruk, О.І. Mayeva, S.V. Mamykin, M.V. Sosnova

 Short description:  Tested liquid with unknown refractive index has to be placed into the glass prism of trapezoidal profile. Laser beam goes through the prism and is being refracted on the output. So, the angle of light incidence on the sensor-photodetector depends on the refractive index of liquid. Photocurrent of the photodetector is greatly dependent on the angle of light incidence due to Surface Plasmon Resonance. Therefore, the strong dependence of photocurrent on refractive index is obtained.

Obtained parameters of Au/GaAs sensitive element
Parameter                                                                        Value
Structure                                                                               Au/GaAs
Light wavelength to work for                                                 650nm
Grating period                                                                       800 nm
The limit of sensitivity to refractive index of tested liquid , Δn    0.001

Fig.1. Design of the device for the measurement of refractive index of liquids
1- light path in the absence of liquid:
2- light path in the presence of liquid;
Uph- output voltage (signal)

Fig.2. Angle dependence of the photocurrent of Au/GaAs senstive element measured for different media:  1 - air; 2-water; 3- mixture of ethanol in the water 50%; 4- pure ethanol.	Fig.3.  Dependence of the photocurrent maximum position (see Fig.2) on the refractive index of liquid.

Fig.4. The photo of the device.
 Red line shows the light path of the laser
1- the laser λ =650 nm
2- the container for liquid of triangle prism shape
3- the cylindrical lens
4- the sensitive element with holder and preamplifier
5- the system for signal processing and indication.

Dimensions: 305mm*75mm*95mm.   Weight: 0.4 kg.