INTERFERENCE BETWEEN SPONTANEOUS 2-PHOTON RADIATION FROM 2 MACROSCOPIC REGIONS

Interference is observed between the spontaneous parametric radiation from two nonlinear crystals separated by a macroscopic air gap and exc ited in series by a common pump beam. The phase of the interference de pends on the phase shifts at three frequencies. A simple quantum model agrees well with the experimental results and makes it possible to in terpret the effect in terms of general vacuum fluctuations which give rise to the spontaneous emission of mutually coherent radiation from t he two crystals. (C) 1997 American Institute of Physics.