Ultra-precision cutting process of the diffractive mold core

The application of diffractive optical elements in optical systems can effectively correct chromatic aberration and improve imaging quality. The processing accuracy and diffraction efficiency of diffractive optical elements can determine the application range of diffractive optical elements. The injection molding process can greatly reduce the manufacturing cost of diffractive optical elements. The surface accuracy of injection molded diffractive optical elements is largely guaranteed by the surface accuracy of the mold core. In order to improve the diffraction efficiency of the shaped diffractive optical element, higher requirements are placed on the machining accuracy of the diffractive optical core. Therefore, this paper studies the ultra-precision turning process of diffractive optical element die core. Firstly, the relationship between the processing parameters and the manufacturing error of the diffractive optical element core is constructed. Then, based on the relationship between the processing parameters and the manufacturing error, the mathematical relationship model between the processing parameters and the diffraction efficiency is constructed. A method for optimizing the height error, period width error and surface roughness of the microstructure during the processing of diffractive optical cores is proposed. Based on this method, an ultra-precision cutting experiment was carried out on the nickel-phosphorus surface with a diffraction grating die core with an aperture of 15 mm. The machining results of the period width error are 6.1μm, the microstructure height error is 0.0454μm, the surface roughness of Ra is 0.816nm and root mean square (RMS) is 1.06nm. Under the experimental results of surface quality, the polychromatic integral diffraction efficiency of the diffractive optical element can reach 98.7 % in the range of 0.45-1.2μm. The results show that the optimization method applied in this paper can ensure the key performance indexes of the diffractive optical element, the machining accuracy and diffraction efficiency of the shaped diffractive optical element can be improved. It lays the foundation for the ultra-precision cutting of the diffractive optical element and the diffractive optical element. Besides, this research can expand the application range of the diffractive optical element.