Near-infrared refractometry of liquids by means of waveguide Čerenkov second-harmonic generation

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Abstract
A new, to our knowledge, method for measuring the refractive index of liquids in the near infrared by means of waveguide Čerenkov second-harmonic generation is presented. It makes use of a nonlinear planar waveguide whereby the liquid sample is put into place as the cover. By measurement of the output angle of the Čerenkov radiation mode (in the visible) the liquid sample refractive index (in the near infrared) is determined. Experiments were performed by means of a proton-exchanged LiNbO3 waveguide as the sensor and a set of liquids with known refractive index. The values obtained are in good agreement with the expected ones, and the average accuracy is on the third decimal place.