Experimental study of induced temporal coherence in parametric down conversion with multimode laser pump

We investigated the phenomenon of induced temporal coherence in optical parametric down conversion. We used a multimode blue-diode-laser pump and a single-mode laser for the injection signal beam. The temporal coherence of the idler beam is known to depend on the coherence function of the pump, the coherence function of the injection beam, the phase-matching condition, and the average photon number of the injection laser beam. Our experimental data show very good agreement with the multimode theory which predicts the changing the spectral shape as a function of the average photon number of the injection beam.