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Description
This work investigates the influence of laser repetition rate, pulse number, and fluence on surface-structure formation in PVA/AA and Biophotopol photopolymers under femtosecond laser irradiation [1]. By analyzing the dependence of structure height on the irradiation parameters, different growth efficiencies associated with monomer diffusion are identified, providing further insight into repetition-rate effects during ultrafast laser-induced photopolymerization [2]. These results demonstrate that micro- and nanostructures can be fabricated in these materials more rapidly and with greater control than in other dielectrics, metals, or semiconductors, making them promising candidates for functional and biomimetic surfaces.
Experiments were performed using a 120, 220 and 450 fs laser at (800, 1030 and 515 nm, respectively) operating from single-pulse to 1 MHz repetition rates by varying the fluence. The photopolymer films (~110 µm thick) were prepared following the standard formulation reported in Ref. [3]. Laser irradiation induces radical generation, monomer polymerization, and diffusion-driven formation of surface relief structures.
Figure 1. (a) 3D representation of the structure generated on the surface of PVA/AA after irradiating with N = 1 pulse and F = 1.25 J/cm2. (b) Measured heights of the structures induced on the surface of PVA/AA irradiations as a function of the fluence for N = 1 (blue), N = 2; 1 kHz (orange) and N = 2; 60 kHz (yellow).
Figure 1a shows a 3D confocal microscopy image (N = 1; F = 1.25 J/cm²) revealing a Gaussian-like surface profile characteristic of diffusion-driven monomer redistribution. Figure 1b presents the dependence of the structure height on fluence for three irradiation conditions: N = 1, N = 2 at 1 kHz, and N = 2 at 60 kHz. The results demonstrate that structure height increases with both pulse number and fluence. However, for the same number of pulses, structures produced at 1 kHz are significantly higher than those obtained at 60 kHz, indicating that repetition rate strongly affects monomer diffusion. The longer interval between pulses at lower repetition rates promotes more efficient monomer transport towards the irradiated region, enhancing structure growth. These findings highlight the interplay between photopolymerization and monomer diffusion, showing that repetition rate governs the balance between polymer formation and monomer transport, thereby determining the final surface morphology.
Acknowledgements
This work was supported by the Spanish MCIN/AEI and ERDF/EU through projects PID2024-161610OB-I00 and+ PID2023-148178OB-C22; by the Generalitat Valenciana (CIPROM/2024/90); the EU Horizon Europe programme (NFFA-Europe, Grant No. 101007417, Access Proposal ID894); and the Provence-Alpes-Côte d’Azur Regional Council (INTENSITY 2022). A.P.B. and I.S. acknowledges a predoctoral fellowships (PRE2022-105016 and FPU23/01300) from the Spanish MCIU. This work was carried out using the LaMP facilities at LP3.
Notes and References
1 M. Malinauskas, A. Žukauskas, S. Hasegawa, Y. Hayasaki, V. Mizeikis, R Buividas, S. Juodkazis, Light-Sci. Appl., 5 (2016).
2 T. Babeva, I. Naydenova, S. Martin, V. Toal, Opt. Express 26, 8487–8497 (2008)
3 A. P. Bernabeu, J. C. Bravo, J. J. Sirvent-Verdú, B. Nieto-Rodríguez, D. Puerto, S. Gallego, Polymers 18, 46 (2025)