Finding a Novel Borate Ferroelectric with Random Domain Structures for Deep‐UV Quasi‐Phase‐Matching

Finding competitive nonlinear optical (NLO) crystals for practical deep‐ultraviolet (deep‐UV) lasers remains a fundamental yet challenging goal in photonic materials research. The production of deep‐UV lasers through the mesoscopic domain structure of ferroelectric materials has been a popular research area via quasi‐phase‐matching (QPM). However, as of right present, no ferroelectric in the deep‐UV area is able to provide QPM laser output. Here, a new room‐temperature borate ferroelectric Ba 3 Mg 3 (BO 3 ) 3 F 3 (BMBF) is presented. The ferroelectricity of BMBF crystals exhibits significant relaxor behavior and the random domain structure can relax the strict phase‐matching conditions, rendering it a disordered NLO medium. Benefiting from its unique ferroelectric properties, BMBF crystal achieves a second‐harmonic generation output energy of 3.55 µJ for 398 to 199 nm wavelength frequency conversion, even in the absence of birefringent phase‐matching conditions. This result demonstrates that BMBF is a promising candidate for deep‐UV QPM applications. Furthermore, this study expands the frontiers of borate ferroelectrics while the realization of deep‐UV light output using BMBF crystal motivates and provides a path for its broader application.