High-resolution grayscale printing on Ge thin films via two-beam direct laser writing

Grayscale lithography is crucial for micro-optical component fabrication but faces challenges in resolution and cost. Conventional methods are diffraction-limited, while phase-change materials often require complex processing. This work presents germanium (Ge) thin films as a versatile platform for maskless grayscale printing. A custom dual-beam direct laser writing system is developed, using a 450 nm auxiliary laser for localized preheating and a 405 nm writing beam for patterning. The writing laser modulates grayscale tones by adjusting surface roughness, oxidation level, and crystallization. This dual-beam setup enables high-resolution, multilevel printing with a maximum resolution of 7.9×10⁴ DPI, enhancing thermal control. Arbitrary grayscale images are successfully fabricated, establishing Ge thin films as a promising medium for high-resolution grayscale lithography.