Recently, Weina Han, Academician Jiang Lan, and colleagues from Beijing Institute of Technology published a paper in Advanced Materials proposing a phase-modulated femtosecond laser non-diffractive beam lithography technology.
By superimposing axial prism phase with blazed grating phase, the femtosecond laser is reshaped into a quasi-Bessel non-diffractive beam with a depth of field exceeding that of tightly focused Gaussian beams by more than tenfold. This reduces the need for refocusing during processing and suppresses focal drift. Dynamic beam deflection control achieves precision down to 7 nanometers. Subsequent chemical processing of the voxel metasurface, formed by phase-change regions, enables mask-free lithography.
This technology was used to fabricate a tunable Ge₂Sb₂Te₅ metasurface with structural features down to 9 nanometers. It further enabled the fabrication and control of multifunctional programmable photonic logic devices, demonstrating high-precision processing capabilities. This approach establishes a new paradigm for fabricating and controlling active metasurfaces, advancing the development of next-generation photonic devices.
Femtosecond Laser Non-Diffracting-Beam Lithography via Phase Modulation for Dielectric Metasurface Fabrication
Phase-modulated femtosecond laser non-diffracting-beam lithography for dielectric metasurface fabrication
Figure 1 Phase-modulated non-diffracting-beam lithography (PNDL) for dielectric metasurface fabrication.
Figure 2 Stability of quasi-Bessel non-diffracting beam generation.
Figure 3: Fabrication precision study of the phase-modulated non-diffracting-beam (PNDL) method.
Figure 4: Lithography of Ge₂Sb₂Te₅ (GST) metasurfaces using the phase-modulated non-diffracting-beam (PNDL) method.
Figure 5: Metasurface device with a dual-rectangular GST superlattice configuration.
The experiment centers on the phase-change material Ge₂Sb₂Te₅ (GST), leveraging its reversible phase transition between amorphous and crystalline states. Using femtosecond laser phase modulation technology, the preparation and control of metasurface structures are achieved. By superimposing axial prism phase and diffractive grating phase via a spatial light modulator, the femtosecond laser (515 nm) is shaped into a quasi-Bessel non-diffractive beam. Focused through a high numerical aperture objective, this beam induces localized crystallization on the GST thin film surface. Subsequently, selective wet etching (TMAH solution) removes non-crystallized regions while preserving crystallized structures, forming metasurface units. By controlling parameters such as laser energy and pixel pitch, high-precision patterning with structural line widths as low as 270 nm and gaps as small as 9 nm was achieved. The dual-rectangular GST superlattice demonstrated multiple logic gate functions upon polarization-excited light.
