Diffraction efficiency is a measure of how effectively a diffractive optical element (DOE) or grating converts incident light into diffracted orders. It is a crucial parameter in the design and performance evaluation of diffractive optical devices, such as beam splitters, wavelength filters, and holograms. Higher diffraction efficiency indicates a more efficient conversion of input light into desired diffracted orders, leading to better overall performance of the device. Researchers in this area focus on optimizing DOE designs, materials, and fabrication techniques to achieve high diffraction efficiency and improve the functionality of diffractive optical systems.