Figure 2: Giant amplification of twin beams along the spatial walkoff.
From: Giant narrowband twin-beam generation along the pump-energy propagation direction
Frequency-angular spectra of type-I PDC from 355 nm pump in a 5-mm BBO crystal (a) show that at orientation 32.97° (as in Fig. 1b,c), only the infrared beam (white dot) propagates along the Poynting vector (green dashed line), but its twin is in the green spectral range (green dot). At orientation 33.7°, the enhanced twin beam is at wavelength 590 nm (yellow dot and Fig. 1e). At orientation 34.9°, the emission at the degenerate wavelength 710 nm is along the walk-off (red dots), and the 2D intensity distribution obtained by a charge-coupled device camera (b) shows hugely enhanced low-divergence twin beams. The rest of the PDC ring is faint and not seen in the linear scale. At other orientations, emission at 710 nm is much weaker, which is shown by logarithmic-scale one-dimensional angular intensity distributions measured (c) and calculated (d) for orientations 33° (red), 34° (green), 34.9° (blue) and 36° (magenta). Slight angular displacement of the right-hand experimental peaks is caused by the large (up to 10°) tilt of the crystal.
