Figure 3: Group matching for type-II PDC in a BBO crystal pumped by 0.9 ps pulses at 400 nm.
From: Giant narrowband twin-beam generation along the pump-energy propagation direction
Tuning curves for the ordinary down-converted radiation are shown for positive angles for crystal orientations 31°, 34.5° and 37.5° (a). For each orientation, at some wavelength the group velocity of the ‘ordinary’ photon matches that of the pump (green arrows). The PDC ring at this wavelength is hugely enhanced if the crystal is long enough (we used four 5-mm BBO crystals stacked together). (b–d) Snapshots of the intensity distributions on a screen placed in the far field, with the angular scale and the crystal orientations the same as in panel a. For comparison, spectra of a single 5-mm crystal with the same orientations show much broader emission spectra (e–g).
