Unique Anamorphic Lens Design Used for Femtosecond Micromachining in Transparent Bulk Materials (Preprint).

摘要

A unique anamorphic lens design was applied to a circular 780nm femtosecond laser pulse to transform it into a narrow line spread at focus. This lens was developed to give an alternative method of micromachining bulk transparent materials. The challenge for femtosecond laser processing is to control the nonlinear affect of self-focusing, which can occur when using a fast f-number lens. Once the focused spot is dominated by self-focusing the predicted focused beam becomes a filament inside the bulk, which is an undesirable effect. The anamorphic lens resolves this self-focusing result by increasing the numerical aperture (NA) and employing an elliptical beam shape. The anamorphic lens was also designed to furnish a 2.5 um by 190 um line spread that will exceed a transparent bulk material's damage threshold in a single femtosecond laser pulse. Damage in this text refers to visual change in the index of refraction as observed under an optical microscope. Using this line spread, grating structures were micro-machined on the surface of SiC bulk transparent substrate.