Power and Bandwidth of Spontaneous Parametric Emission

Abstract

Theoretical and experimental results concerned with the spectral and angular distribution of spontaneous parametric emission are reported. Such emission results when light from a pumping laser is incident on a nonlinear crystal, and does not require that the parametric gain exceed the single-pass crystal loss. The emission is somewhat like spontaneous Raman or Brillouin scattering, but differs in two major respects. First, in a lossless crystal, the bandwidth of the emission is controlled by the crystal length and accepted angular aperture as opposed to a loss mechanism in the Raman or Brillouin case. Second, by changing the crystal temperature or orientation, the spontaneous emission may be tuned over several thousand angstroms. The reported experiments employed a 4880 Å laser as a pump and a 1-cm crystal of LiNb${\mathrm{O}}_3$ as the non-linear material. The application of parametric spontaneous emission to the measurement of crystal non-linearities is considered, and the advantages of this method over second-harmonic generation are discussed.