Study of the optical rotatory of potassium titanyl phosphate using the advanced dual-wavelength polarimetric method

A dual-wavelength high-accuracy universal polarimeter was applied to the circular birefringence and optical activity measurement in potassium titanyl phosphate (KTP) nonlinear crystal. The experimental setup used two single-mode He-Ne lasers with close wavelengths of 594 and 633 nm as light sources. Measurement has been carried out for two crystal settings in directions of a 45-degree relative angle to the [100] and [010] crystallographic axes. Multiple light reflections inside the crystal sample were considered when processing the results of the polarimetric measurements. The results have been analysed using the optical transmission function for the polariser-sample-analyser system, and 2D intensity contour maps made it possible to determine the phase parameters, systematic errors, and eigenwaves ellipticity. It was found that the gyration tensor component of the KTP crystal is equal to g12 = 1.4 ⋅ 10−5 which in terms of optical rotatory power corresponds to the very small magnitude of the rotation value of 2.3 deg/mm.