We report the simultaneous quasi-phase-matching of all three possible nonlinearities for propagation along the X axis of periodically poled (PP) KTiOPO4 (KTP) for second-harmonic generation of 745 nm pulsed light from 1490 nm subpicosecond pulses in a PPKTP crystal with a 45.65 µm poling period. This confirms the recent Sellmeier fits for KTP by Kato and Takaoka [Appl. Opt.41, 5040 (2002)]. Such coincident nonlinearities are of importance for realizing compact sources of multipartite continuous-variable entanglement [Pfister, Phys. Rev. A70, 020302 (2004)], and we propose a new simpler method for entangling four fields on the basis of this triple coincidence.
© 2005 Optical Society of America
Raphael C. Pooser and Olivier Pfister, "Observation of triply coincident nonlinearities in periodically poled KTiOPO4," Opt. Lett. 30, 2635-2637 (2005)