Figure 1: Beamlike PDC along the pump spatial walk-off.
From: Giant narrowband twin-beam generation along the pump-energy propagation direction
The highest gain is achieved for emission along the pump Poynting vector, which inside the crystal is non-collinear to the wavevector (a). The optic axis direction is schematically shown on top of the crystal. Snapshots with a photographic camera (b–f) show the spectra of high-gain PDC at different crystal orientations: 32.97° (b,c), 33.4° (d), 33.7° (e) and 34° (f). The angular scale is shown in panel b; the grid is the same for all panels. Additional stripes in d,e are due to the reflections in the crystal. Emission at the walk-off angle and in the phase-matched direction is enhanced. This occurs, at different crystal orientations, for different colours (d–f). A snapshot with a neutral-density filter (c) shows colours without the saturation.
