Transparent Lead-Free Ferroelectric (K, Na)NbO_3 Single Crystal with Giant Second Harmonic Generation and Wide Mid-Infrared Transparency Window

摘要

Environment-friendly lead-free potassium-sodium niobate (KNN) has become one of the most extensively investigated ferroelectrics in the past decade, while high transparency KNN single crystal has never been realized yet. Here, a transparent KNN single crystal is successfully grown by the top seeded solution growth method. The KNN crystal possesses a very wide transmittance range of 0.37–8 μm, completely covering the important mid-infrared atmospheric transparent window (3–5 μm). Noticeably, the KNN crystal exhibits the largest second-harmonic generation efficiency (7.6× that of potassium-titanyl phosphate (KTP)) with type-I phase matchability under the fundamental wavelength of 1064 nm among all of the studied mid-infrared oxide nonlinear optical crystals reported so far. This work demonstrates a novel mid-infrared nonlinear optical oxide crystal with a giant second-harmonic generation and wide transparency range, providing a new idea for the exploration of nonlinear oxide crystals.