Two-photon lithography (TPL) is a direct write technique that enables fabrication of macroscale complex 3D structures with submicron features. In this process, writing of complex structures is achieved through a serial writing technique wherein a high light intensity spot is sequentially scanned in 3D space to generate the entire structure. Due to the serial writing scheme, the rate of writing is fundamentally limited to such an extent that two-photon lithography of large volumes of functional parts is not feasible. Although attempts to increase the rate via parallelization have been made in the past, such attempts have failed to achieve the same degree of pattern complexity as that available in the point-scanning serial technique. Specifically, past parallelization efforts have either generated arrays of identical features or printed 2D parts with no depth resolvability.
LLNL has solved the challenges of depth-resolved parallel TPL by using a temporal focusing technique in addition to the spatial focusing technique used in serial writing systems. We temporally focus the beam (through optical set-up design) so that a sharp Z-plane can be resolved while projecting 2D “light sheets” that cause localized photo-polymerization. This enables printing of complex 3D structures in a parallel fashion. To minimize the errors arising from discretization of 3D structures, LLNL has also developed techniques to “bend” the 2D light sheet into a 3D surface for printing of curved features.
The inventive elements of the LLNL apparatus are the arrangement of the laser light, the digital mask, and the axis of the collimating optics and the relative size of the collimating optics to ensure that temporal focusing of the projected light sheet is achieved.
The Livermore innovative technology also comprises the grayscale printing method that ensures that high-quality parts can be fabricated. Our grayscale printing technique comprises the sequence of operations and the selection of writing conditions in these operations that leads to a non-uniform dosage during printing.
LLNL parallel two-photon lithography technique ensures a depth resolution less than 5 microns and an in-plane feature size less than 350 nm. The LLNL technique appears functionally similar to DMD-based parallelization in projection micro-stereolithography systems, however it implements a fundamentally different optical system to ensure that the light sheet is both spatially and temporally focused.
By overcoming the barrier to depth resolvability in femtosecond projection optics, LLNL has successfully increased the rate by a factor of 50X while still maintaining the less than 350 nm feature size resolutions of high-quality serial techniques. In addition, bending of the light sheet into 3D surfaces minimizes discretization errors during printing of curved structures. The LLNL techniques eliminate a fundamental barrier to scaling up submicron additive manufacturing and transforms two-photon lithography into a serious contender for high-volume additive manufacturing of functional parts with nanoscale features.
- Fabrication tool and technique for submicron additive manufacturing
- 2D and 3D printer for microelectronics industry
- Fabrication of high-energy laser targets
- 3D printer for printing of photonic crystals (sensors), mechanical metamaterials (low-density, high-strength, engineered metamaterials), microfluidics (for biomedical diagnostic chips).
LLNL has patents pending for this technology (internal case numbers ILs13220 & 13266).
This technology was presented at the Photonics West 2018 conference in San Francisco during a technical talk on Jan 29, 2018 (Paper 10544-23).