Negative Polarisation in Fluorescence

Abstract

IN an important paper¹ Wawilow has reported measurements on the polarisation of fluorescence of solutions of some dye-stuffs in glycerine, when excited by radiations of different wave-lengths. Using for excitation the radiations from a mercury lamp, isolated by a quartz monochromator, he finds that the degree of polarisation shows a marked dependence on the wave-length of the exciting light. Starting from the visible region of the spectrum, as the wavelength of the exciting light is diminished the degree of polarisation decreases rapidly, passes through a minimum value (corresponding, in genera], to excitation by λ3125–3131), and rises again as we proceed farther towards the ultra-violet. The minimum value is usually negative; that is, the intensity of the fluorescent vibrations along the direction of propagation of the incident light is greater than that of vibrations in the perpendicular direction.