Phosphogermanate Crystal: A New Ultraviolet–Infrared Nonlinear Optical Crystal with Excellent Optical Performances

The
phase matching ability is a key factor for nonlinear optical
crystals to realize coherent output. Herein, a new design strategy
combining ultraviolet and infrared functional groups into a ferroelectric
was put forward. Thus, a phosphogermanate crystal, KGeOPO4, was designed and studied. It exhibits a wide transparency window
(0.22–9.70 μm), a strong second harmonic generation response
(5× KH2PO4), a high laser-induced damage
threshold (1.61 GW/cm2), and the typical ferroelectricity
(coercive field ∼ 9.8 kV/cm and remnant polarization ∼7.6
μC/cm2). In the infrared region, it could realize
coherent output by the birefringence phase matching method, while
it could generate ultraviolet coherent lights by the quasi-phase matching
technique. Therefore, this work designs a promising ultraviolet–infrared
nonlinear optical crystal and provides a new perspective for exploring
nonlinear optical crystals.