Polymerization Photoinitiators with Near-Resonance Enhanced Two-Photon Absorption Cross-Section: Toward High-Resolution Photoresist with Improved Sensitivity

Abstract

We take advantage of the near-resonant enhancement of the third-order nonlinear response to engineer a two-photon polymerization photoinitiator with optimized efficiency in regard to literature benchmarks. We study in detail its linear and resonant third-order nonlinear optical properties, with particular focus on photoinduced radical generation. Careful choice of peripheral substituents enables its direct solubilization into a mixture of commercial multifunctional acrylic monomers, resulting in a homogeneous photoresist with good optical transparency upon simple mixing. When submitted to sub-nanosecond pulsed laser irradiation at 532 nm, the resulting photoresist displays a polymerization threshold up to eight times lower than that obtained with the classically used two-photon initiators, giving rise to sub-100 nm line width at 250 nm interline separation and resulting in highly defined three-dimensional structures.

Understanding and overcoming proximity effects in multi-spot two-photon direct laser writing

“…All reagents were used without further purification. Three resins were used in this study based on the use of a photoinitiator (PI) previously reported by our team [32,33]: PR_organic (DPPHA/DDA/V-Shape, weight ratio: 79.2/19.8/1, includes ca. 600 ppm MEHQ as stabilizer/polymerization inhibitor), PR_hybrid (PI-free Ormocomp/V-Shape, weight ratio: 99.5/0.5, stabilizer free) and stabilized PR_hybrid (PI-free Ormocomp/V-Shape, weight ratio: 99.5/0.5 + 700 ppm MEHQ).…”

Rapid, continuous projection multi-photon 3D printing enabled by spatiotemporal focusing of femtosecond pulses

“…Another limiting factor for achieving high printing rates is the sensitivity of the photoresist. Much work has been done to develop two-photon photoinitiators with improved photoinitiating capabilities [48][49][50][51] .…”

Fabrication of Functional Microdevices in SU-8 by Multi-Photon Lithography

“…The TPA cross section σ 2 is often represented as “ δ ” and has units of m 4 s molecule −1 photon −1 , typically expressed in units of “GM” (1 GM = 1 × 10 −58 m 4 s molecule −1 photon −1 ). Augmenting polarizability of PAGs by judicious incorporation of donor/accepter moieties can increase δ up to two orders of magnitude [ 28 , 38 , 39 , 40 ] compared to that of common UV initiators [ 41 ]. Increasing δ enhances the sensitivity of the resin and enables fabrication at lower powers.…”