Optical freeform generation of N-BK7 by fluorine‐based plasma jet machining

The production of complex shaped optical elements like non-standard aspheres, acylinders, or freeform elements are highly demanded. Thus, optical manufacturing technologies need to be developed for optical systems to design freeform surfaces. Reactive Plasma Jet (RPJ) is one of the most promising tools for freeform generation of fused silica, SiC, ULE® and silicon. However, there are severe limitations when this technique is used for the surface machining of optical glasses like N-BK7®. The chemical interaction between plasma generated active species and metal components of N-BK7 induces the formation of a residual layer in the plasma-surface contact zone and surrounding which can degrade the capability of acquiring the required surface profile. It is shown that elevated surface temperature can modify the residual layer leading to higher predictability of freeform machining results.