Interference between independent light beams of small intensity

Leonid A. Vainshtein, V.N. Melekhin, S. A. Mishin +1 more

V. V. Mityugov, V. P. Morozov

Wolfgang Radloff

Abstract We have observed the interference between two independent single mode He‐Ne laser beams. Our special equipment allowed us to record many times the interference pattern, when it was standing for a short time at the same position on the recorder. In this way we have obtained an interference picture of two independent light beams, which was (a) visible directly for the unaided eye for large intensities, (b) recorded on a photographic film for low intensities. The result of the experiments were in agreement with the statement of the quantummechanical description: We found a classical interference pattern down to very small intensities of the superposed beams. This result is discussed with regard to the quantum structure of light.

Jianbin Liu, Jingjing Wang, Zhuo Xu

The second-order temporal interference of classical and nonclassical light at an asymmetrical beam splitter is discussed based on two-photon interference in Feynman's path integral theory. The visibility of the second-order interference pattern is determined by the properties of the superposed light beams, the ratio between the intensities of these two light beams, and the reflectivity of the asymmetrical beam splitter. Some requirements about the asymmetrical beam splitter have to be satisfied in order to ensure that the visibility of the second-order interference pattern of nonclassical light beams exceeds the classical limit. The visibility of the second-order interference pattern of photons emitted by two independent single-photon sources is independent of the ratio between the intensities. These conclusions are important for the researches and applications in quantum optics and quantum information when an asymmetrical beam splitter is employed.

Lajos Jánossy, Zs. Náray

L. Mandeļ

The conditions are examined under which interference effects should be observable in the superposition of two light beams derived from independent sources. The quantum-mechanical description of these effects differs from the classical description principally in that it is necessarily based on expectation values of the light intensity at one or more space-time points. It is shown that pure states of the radiation field which are not energy states give rise to interference effects, but in that case the two beams cannot meaningfully be described as statistically independent. For a realistic description mixed states have to be introduced, when the expectation value of the intensity gives no indication of interference effects. On the other hand, the intensity correlation at two space-time points is a periodic function of the separation of the points and indicates the presence of transient interference effects. The effects become readily observable only when the average photon occupation number of each cell of phase space is appreciably greater than 1, and this explains why laser beams were needed for the experimental observations. It is pointed out that, even in these experiments, each photon may be regarded as interfering only with itself.