Measurement of angular distribution of radiation from dye molecules coupled to evanescent wave

Abstract

We measured the angular distribution of spontaneous emission radiation from dye molecules near a plane boundary. We found a systematic change of the angular distribution depending on the pump beam angle. By comparing the experimental results obtained by normal pumping and evanescent pumping, we could discern between the characteristics of radiation from the molecules within subwavelength distance from the boundary and that from the molecules relatively far from the boundary. It is found that the exact shape of the angular distribution of radiation is determined by the local geometrical factor related to the pump beam angle and the radiation detection angle. The characteristics of the spontaneous emission beyond critical angle and the measured polarization dependence of the radiation are in good agreement with the triplet mode quantum theory, as well as semiclassical theory.