As freeform optical system design pushes fabrication limits, manufacturing approaches must provide higher flexibility and deterministic precision. Conventional glass figuring relies on contact-based, multi-step processes such as milling and grinding, which introduce subsurface damage and require chemical polishing for mitigation. Tool size further limits sub-aperture feature fabrication as dimensions decrease. Diamond turning offers precision but is difficult to apply to brittle materials such as glass, and residual tool marks lead to persistent mid-spatial frequency (MSF) errors. Non-contact techniques, including ion beam figuring and plasma jet polishing, require stringent environmental control, increasing cost and limiting reliability.

Laser-based fabrication has emerged as a non-contact, flexible, and precise approach that avoids chemical processing and extensive environmental constraints. Ultrafast lasers deliver high peak power with low average power, enabling nonlinear absorption and athermal material removal with minimal thermal damage. Direct femtosecond laser fabrication developed at the Qiao lab has demonstrated sub-nanometer surface polishing and nanometer-level material removal control [1], along with MSF error mitigation [2] and deterministic fabrication of micro-scale structures [3].

In this work, calibrated material removal is integrated with deterministic shape prediction to fabricate a freeform surface on Borofloat 33 glass. A root-mean-square (RMS) error of 1 nm relative to the target profile is achieved. The fabrication method and process are presented.

[1] G. Chen and J. Qiao, Opt. Lett. 47(15), 3860 (2022).

[2] G. Chen and J. Qiao, Opt. Lett. 49(6), 1560 (2024).

[3] G. Chen et al., Opt. Express 33(11), 23252 (2025).