Lens element for a microlithographic projection exposure apparatus designed for operation in the duv, and method and arrangement for forming an antireflection layer

A method for forming an antireflection layer on a lens element substrate of a lens element for a microlithographic projection exposure apparatus designed for operation in a Deep Ultraviolet (DUV) wavelength range, the method comprising:

• providing a lens element substrate;
• and
• forming the antireflective layer on the lens substrate from a first material of relatively lower refractive index and at least one second material of relatively higher refractive index, wherein a mixing ratio between the first material and the second material is varied in a lateral direction and/or in a vertical direction, and wherein the antireflection layer is formed using separate evaporation sources for the first and second materials, wherein the material from these evaporation sources is respectively supplied via an intermittently open shutter.