Accounting for the imperfection of the spectrophotometric complex optical elements when measuring transmission spectra of gyrotropic uniaxial crystals. II. Samples are cut parallel to the optical axis

A theoretical and experimental study of the effect of imperfections of the polarizer, analyzer and photomultiplier tube (PMT) on the measurement results of the transmission coefficient spectra of the langasite family crystals cut parallel to the optical axis has been carried out. It is shown that in the absence of an analyzer, oscillations appear on the transmission spectra, the amplitude of which depends on the rotation of the crystal. These oscillations are associated with linear birefringence and appear due to the imperfection of the PMT, which plays the role of a partial analyzer. From the obtained spectra, the parameters of the PMT are calculated depending on the wavelength. The calculation of the birefringence of the studied crystals was carried out and an estimate of the error of such calculation was obtained. It is shown that the imperfection of optical elements does not lead to additional errors in the calculation of birefringence. Thus, when the plate is cut perpendicular to the optical axis, circular birefringence is manifested, when parallel, there is linear birefringence.