Challenges and Opportunities in 3D Laser Printing Based on (1 + 1)-Photon Absorption

Abstract

Most light-based 3D printing methods rely on optical or chemical nonlinearities to spatially confine the polymerization reaction. In 3D micro-and nanoprinting, this nonlinearity can be provided by two-photon absorption, which describes the simultaneous absorption of two photons. To achieve comparable absorption cross sections for two-photon as in onephoton absorption, short and intense laser pulses with intensities in the range of 1 TW/cm 2 are typically required. Herein, we review three emerging excitation processes that provide a quadratic nonlinearity versus intensity without relying on two-photon absorption: upconversion luminescence, two-step absorption, and triplet−triplet annihilation. We term these "(1 + 1)-photon absorption". Such processes allow for using continuous-wave lasers at much lower peak laser powers and at much lower cost than those typical for two-photon absorption. We review recent progress, describe current challenges, and outline future perspectives.

Nanoengineering Triplet–Triplet Annihilation Upconversion: From Materials to Real-World Applications

“…The majority of stereolithographic processes require UV light for absorption by the photoinitiator in the resin to initiate polymerization, generally limiting printing to the surface of the print volume. Volumetric 3D printing can enable the printing of complex shapes without relying on a layer-by-layer process, eliminating the need for support structures, speeding up the print process, and reducing waste. , Taking advantage of nonlinear processes can enable volumetric 3D printing: ,, for instance, two photon polymerization (2PP) is a commercially available technology in which two low energy IR photons generate a high energy state to ultimately initiate the photopolymerization by means of electron transfer. , While excellent resolution at the nanoscale is achievable, limits in fundamental material properties (e.g., potential for dielectric breakdown due to requisite pulsed lasers), and volumes limited to the mm 3 scale prevent the widescale adoption of this technology. ,,, …”

“…Volumetric 3D printing can enable the printing of complex shapes without relying on a layer-by-layer process, eliminating the need for support structures, speeding up the print process, and reducing waste. 179,180 Taking advantage of nonlinear processes can enable volumetric 3D printing: 172,181,182 for instance, two photon polymerization (2PP) is a commercially available technology 183 in which two low energy IR photons generate a high energy state to ultimately initiate the photopolymerization by means of electron transfer. 184,185 While excellent resolution at the nanoscale is achievable, limits in fundamental material properties (e.g., potential for dielectric breakdown due to requisite pulsed lasers), 172 TTA-UC-driven photopolymerization shows promise for volumetric printing by addressing the limitations mentioned above.…”

“…https://doi.org/10.1021/acsnano.3c00543ACS Nano XXXX, XXX, XXX−XXX limited to the mm 3 scale prevent the widescale adoption of this technology.2,174,182,186 …”

Two‐Photon Polymerization Lithography for Optics and Photonics: Fundamentals, Materials, Technologies, and Applications

“…Combining one‐ and two‐photon polymerization is also a feasible way for photonic integration. [ 754 ] Moreover, with the recent development of cw laser polymerizable photoresists, [ 755–757 ] cost‐effective and high‐power 3D TPL printing systems may bring new possibilities for industrial mass production, and also minimization into highly integrated equipment. [ 758 ]…”

“…Combining one-and two-photon polymerization is also a feasible way for photonic integration. [754] Moreover, with the recent development of cw laser polymerizable photoresists, [755][756][757] cost-effective and high-power 3D TPL printing systems may bring new possibilities for industrial mass production, and also minimization into highly integrated equipment. [758] In addition, multimaterial printing is promising as different parts of the structure can be fabricated and integrated within one step for multifunctional applications.…”