Quasi-phase-matched frequency conversion in KNbO3 structures consisting of 90° ferroelectric domains
Periodic 90° domain structure with 18.6 μm periodicity was fabricated by applying a 200 V/mm electric field over (1̄01)-cut KNbO3 plate. The blue light generation by quasi-phase-matched frequency doubling in this periodic 90° domain structure is demonstrated. The 90° domain structure completely compensates for a Poynting vector walk-off of the second-harmonic beam. Moreover, these structures exhibit amphoteric Poynting vector refraction properties, i.e., the refraction can be negative or positive depending on the angle of incidence at the 90° domain boundary.
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