Direct measurement of Two-Photon Absorption and Refraction properties of SZ2080™-based resists at 515 nm: insights into 3D printing

The two-photon absorption (TPA) and non-linear refraction coefficients β and n ₂ of SZ2080 ^TM resist with the photo-initiators (PI) IRG369 and BIS (Irgacure 369 and 4,4' bis(diethylamino)-benzophenone or Michler’s ketone) are determined using the Z-scan method at a wavelength of 515 nm. The nonlinear response of the host polymer is shown to have a considerable contribution to energy deposition despite the addition of the PI, as the host polymer makes up the majority of 99% in the solution. TPA cross section σ = 5.7 ± 0.4 GM (1GM = 10 ^-50 cm ⁴ sphoton ^-1 ) for pure SZ2080 ^ΤΜ , 40 GM for IRG and 87 GM for BIS at 515 nm. The positive n ₂ = (85.3 ± 6) × 10 ^-5 cm ² /TW for pure polymer favors self-focusing and is larger than that for PIs: 16 × 10 ^-5 cm ² /TW (IRG369) and 2.8 × 10 ^-5 cm ² /TW (BIS). Hence, the properties of the host material govern non-linear light propagation, although, in high numerical aperture focusing, the self-focusing has a negligible effect. Z-scan experiments were carried out at a low 1 kHz laser repetition rate to exclude thermal accumulation at the focal region. These findings will allow for the estimation of exact energy deposition in 3D laser printing using ultrashort laser pulses.