De-coherent parallel laser processing of ultradense nanopores for high-density, large-area 3D optical phase encoding.

Abstract

Single-beam femtosecond laser pulses can surpass the diffraction limit of conventional focusing systems, enabling deep sub-waveguide single-spot modifications via nonlinear absorption at the focus. However, extending this capability to multi-beam parallel processing has been fundamentally limited by the diffraction limit (~λ/2). Herein, we experimentally and theoretically clarify that this limitation stems from spatial coherence and temporal sequence interference, inducing laser-matter interaction crosstalk, non-uniform modifications, and sparse duty-cycle structures. To address this, we propose a de-coherent parallel direct laser writing (Dc-PDLW) strategy, utilizing a patterned single pulse together with a de-coherent holographic algorithm (SSP-BM) to ensure multi-foci polarization orthogonality and eliminate spatial coherence. This method achieves single-shot fabrication of ultra-dense nanopore arrays, with 300 nm (~λ/4) resolution in crystals. We further demonstrate centimeter-scale 3D Pancharatnam-Berry phase plates and voluminous cipher sequences, realizing high-density 3D phase and polarization coding.