Ga(IO3)3: a mid-IR nonlinear optical iodate with balanced performance between band gap and second harmonic generation response

Abstract

The balance between band gap and second harmonic generation (SHG) response, which are usually inversely related, is the key factor for achieving good performance in a mid-infrared (mid-IR) nonlinear optical (NLO) crystal. Still it remains a challenge to achieve this balance, which strongly hinders the development of mid-IR solid-state lasers. In this work, utilizing an aliovalent substitution strategy of functional units, we successfully realize mid-IR NLO balanced performance in a chiral iodate, Ga(IO₃)₃, which simultaneously exhibits a strong SHG response (13 × KDP) and a wide optical band gap (3.94 eV). The first-principles calculation is also performed to elucidate its NLO origin. Combining the experimental measurements and theoretical calculations, it is clear that Ga(IO₃)₃ possesses excellent comprehensive NLO performance including a strong SHG effect, a wide band gap, good thermal stability (450 °C), and a large birefringence, indicating its potential applications as a mid-IR NLO crystal.