Ultrafast laser plasma dynamics enabled ultrafine vertical nanochannel array in transparent materials

Abstract

The direct fabrication of vertical nanochannels with ultrahigh aspect ratios (1000:1) in transparent materials has long been hindered by diffraction-limited focal spots and plasma-induced instabilities inherent to conventional ultrafast laser processing. To address these challenges, we introduce a dynamic focusing homogenized light field technique, which integrates a high-refractive-index optical medium to compress the laser focal spot below the diffraction limit (∼700 nm) while leveraging nonlinear Kerr effects to elongate the axial energy distribution. This approach dynamically redistributes energy spatiotemporally, suppressing plasma explosion pressures by 86 % (1440 nm vs. 192 nm) and enabling deterministic control over nanochannel geometry. Through dual-temperature equation simulations and time-resolved plasma spectroscopy, we establish a predictive framework linking processing parameters—such as cover glass thickness, pulse width, and energy—to nanostructure dimensions, achieving aspect ratio close to 1000:1, exemplified by nanochannels measuring 182 μm in length and 192 nm in width. Key innovations of this technique include nonlinear focal drift engineering, which decouples transverse resolution from longitudinal energy deposition, and a plasma suppression mechanism informed by numerical simulations and spectroscopy, ensuring structural integrity through multi-dimensional light field control. Furthermore, we demonstrate the first single-step fabrication of 3D volumetric diffraction gratings in fused silica with sub-1.25 μm channel spacing and tailored optical responses, such as 35.9 % diffuse transmittance and a 0.52 absorption coefficient at 247 nm. This method transcends traditional trade-offs, offering precision, scalability, and versatility: it achieves sub-100 nm feature control, enables scalable fabrication of complex architectures like through-hole and multi-depth structures, and tailors optical properties for metamaterials in integrated photonics, nanofluidics, and quantum optics. By resolving plasma-driven instability and thermal accumulation, our technique unlocks transformative applications in low-loss waveguides, single-molecule sensors, and topological photonic crystals. This work redefines laser nanofabrication as a universal platform for high-precision, scalable 3D structuring in brittle materials, positioning it as a cornerstone for next-generation optical and quantum technologies.