Measuring the thickness of Z-cut uniaxial crystals based on Bessel laser beams

An optical method for measuring the thickness of z-cut uniaxial crystals is proposed. The method uses a periodic mutual conversion of zero- and second-order Bessel beams observed during their propagation along the optical axis of a uniaxial crystal. The paper presents the theoretical background and features of the practical implementation of the measuring method. The applicability of the method for measuring thicknesses ranging from tens of micrometers up to tens of millimeters is shown for a lithium niobate crystal.