  We introduce a method for finely adjusting the etch depth profile by dynamic
shielding in the course of ion beam etching (IBE), which is crucial for the
ultra-precision fabrication of large optics. We study the physical process of
dynamic shielding and propose a parametric modeling method to quantitatively
analyze the shielding effect on etch depths, or rather the shielding rate,
where a piecewise Gaussian model is adopted to fit the shielding rate profile.
We have conducted two experiments. In the experiment on parametric modeling of
shielding rate profiles, its result shows that the shielding rate profile is
significantly influenced by the rotary angle of the leaf. And the experimental
result of fine-tuning the etch depth profile shows good agreement with the
simulated result, which preliminarily verifies the feasibility of our method.
