We discuss the visibility of Young’s interference fringes for non-stationary fields, such as optical fields considered for a short period of time, and contrast the usefulness of different time-frequency representations to determine this visibility.
We used the focal line of a cylindrical lens illuminated by a collimated expanded He–Ne red laser light as a filamentary light source to observe Young’s interference fringes. When the monochromatic filamentary light source is parallel to Young’s slits, the interference fringes are parallel to them and are well defined and highly contrasted. When the filamentary light source is rotated in a plane parallel to that of the slits, the visibility of the interference fringes is always extremely high, but their geometrical distribution and the distance between them depend on the rotation angle and the observation distance. A simple theoretical model is proposed, based on a cylindrical wave propagated according to the Huygens–Kirchhoff formula. The experimental results coincide remarkably well with the stated theoretical model.
We report an experiment of observation of classical double-slit interference fringes of two-photon interference. In the experiment, a commercial continuous-wave multi-mode F-P laser diode without either mode-locked or frequency-locked is used as the light source, the density of photons is far more than the single-photon level, and the path difference of the long and short paths is far more than the longitudinal coherence length of the laser diode. The temporal stable and clearly visible spatial-distributed pattern, i.e. first-order interference fringes, was observed .Contradict to the prediction of single-photon interference mechanism, the interference happened far beyond the coherence length, the occurrence possibility and time duration of the interference fringes decrease with the reduction of mode number of the LD, and the time difference between the fringes disappearance and the light vanish is equal to the time difference of the two paths. After discussion, we came to the conclusion that the observed phenomena can be understood in time-resolved two-photon interference mechanism. We reveal a new method to perform two-photon first-order interference, and this help to understand the nature of two-photon interference and also can be useful for quantum information science.