Recent advances in self-frequency-doubling crystals

The self-frequency-doubling (SFD) crystal is a representative of multifunctional crystals. In recent years, SFD crystals and lasers have gained renewed attention based on the progress on SFD crystals and lasers and Nd:RECa4O(BO3)3 (RE = Y or Gd) crystals, with SFD lasers becoming commercial products. Here, we review the advances of SFD crystals and lasers, including the basic selection rules, theoretical analysis and recent progress of some potential SFD crystals and lasers. The Nd:RECa4O(BO3)3 crystals and lasers are highlighted, and their applications are also proposed and discussed, which may provide some inspiration for the further development of the SFD field and multifunctional materials.