Abstract

Though it is generally assessed that parametric superfluorescence has very poor spatial coherence, since it arises from the amplification of random-phase quantum noise, studies are in progress of the effect of transverse intensity modulations in the pump beam on the superfluorescence diffraction properties [1]. The present experiment provides the first demonstration of parametric generation of diffraction-limited superfluorescence. It was obtained by focusing the pump (λ_p=527 nm, τ_p - Ips, E_p = 2.5 µJ, M²− 1.2) in a - 60 µm FWHM spot on a 15 mm thick LBO crystal, operated in type I non-critical phase-matching. With such a choice of the pump spot size, the confocal parameter is equal to one half the crystal thickness. Singleshot measurements of signal beam quality were performed by collecting the generated superfluorescence with a focusing lens and recording the intensity distributions at the beam-waist and in far-field, simultaneously. Typical intensity plots are given in the figure for signal at 830 nm, from which a M² value equal to 1.01 was calculated. By measuring the beam divergence, we determined the signal spot size inside the crystal to be 17 µm FWHM. The conversion efficiency was few percents. Note that, by increasing the pump spot size, the signal beam quality soon lowered.

© 1996 IEEE