Abstract

Fourth-order interference effects, especially in the absence of the second-order interference, are often considered to be non-classical phenomena. In this paper we demonstrate such effects observed for light scattered by acoustic waves with quasi-thermal statistics. Even for such a classical situation, the fourth-order interference pattern turns out to provide information that is not contained in the angular intensity distribution. Quasithermal acoustic waves were excited in fused silica using a narrow-band noise electric signal fed to a piezoelement. Light scattered at the Bragg angle was analysed in the far field zone using a Brown-Twiss interferometer with a pair of photon counting PMTs and a coincidence counting cirquit. Scanning one of the PMTs, we measured the angular dependence of the fourth-order correlation function (intensity correlation function) for different sizes of the scattering volume, which was determined by the pump beam diameter. Typically, the intensity correlation function g⁽²⁾ showed interference fringes, which were absent in the intensity distribution I (Fig. 1). The value of g⁽²⁾ in its maximum is close to 2, in accordance with the fact that the scattered light has quasi-thermal statistics [1]. The oscillations become more frequent as the pump beam diameter increases.

© 1996 IEEE