Crystal Structural Editing: Novel Biaxial MgTe₂O₅ Crystal as Zero-Order Waveplates

Waveplates are important optical components to control the polarization of light. Currently, they are often fabricated from uniaxial crystals, and there is no report about waveplates based on the biaxial crystals. In this work, a novel biaxial crystal MgTe₂O₅ with a structure constructed by 0D Te₂O₅ groups is designed and grown as waveplate materials for the first time. The exciting result is that the birefringence in the (001)-plane is smaller than 0.0028 in the range from 0.4 to 5 µm, which is significantly smaller than that of the current waveplate materials. The polarization modulations of the MgTe₂O₅ devices working at 532 nm indicate that excellent zero-order half and quarter waveplates have been successfully prepared. In addition, achromatic waveplates used in the visible, near-infrared, and mid-infrared ranges have also been calculated. The MgTe₂O₅ crystal not only exhibits a high laser damage threshold of up to 2.7 GW cm^-2 but also shows a wide transmission range from 0.37 to 6.3 µm. These results provide an excellent waveplate crystal and explore the applications of biaxial crystals.