image: Figure 1 | Concept of single-pulse anisotropic amorphization lithography (SAAL). a Schematic diagram of SAAL in transparent dielectric crystals. b Basic implementation process of SAAL using isotropic and anisotropic energy sources. Red dotted curves indicate the laser spot profile in the XY plane.
Credit: Bo Zhang et al.
High-efficiency light manipulation inside transparent dielectric crystals is essential for next-generation integrated photonics. However, most existing photonic structures rely on two-dimensional surface processing, while precise three-dimensional structuring inside bulk crystals remains extremely challenging. In particular, nonlinear dielectric crystals such as lithium niobate and quartz possess excellent optical properties but are difficult to modify internally due to their highly stable ionic and covalent bonds and weak linear optical absorption.
In a new paper published in Light: Science & Applications, a team of scientists, led by Professor Jianrong Qiu from College of Optical Science and Engineering, Zhejiang University, China, and co-workers have reported a single-pulse anisotropic amorphization lithography technique that enables direct three-dimensional patterning inside all-inorganic dielectric crystals. By using a single ultrafast laser pulse, the researchers induce a highly controlled amorphous phase transition within the crystal matrix, forming regular sheet-like structures with feature sizes down to 200 nm and aspect ratios as high as 190 to 1.
The key to this breakthrough lies in the ultrafast laser-driven anisotropic thermal deposition enhanced by high-density free electrons. When the femtosecond pulse interacts with the crystal, it excites a transient metallic state in the focal region, dramatically increasing electronic thermal conductivity and enabling strongly anisotropic energy transfer. As a result, highly regular amorphous units can be created in a single pulse without cumulative damage or structural impurities.
“Conventional laser direct writing usually relies on multiple pulses, which often introduce unwanted phase impurities and structural defects,” said Professor Qiu. “Our approach uses a single ultrafast pulse to achieve high-purity amorphization, significantly improving structural regularity and optical modulation efficiency.”
Comprehensive structural characterizations confirmed the formation of sharp phase-transition interfaces and high-purity amorphous regions. By tailoring the spatial profile of the laser beam, the researchers demonstrated precise control over the orientation, length, and arrangement of the amorphous units. Importantly, the method is not limited to a specific material system and has been successfully extended to lithium niobate, quartz, lithium tantalate, yttrium orthovanadate, and potassium titanyl phosphate crystals.
To demonstrate practical functionality, the team fabricated three-dimensional nonlinear photonic architectures for efficient frequency conversion. In lithium niobate crystals, multilayer fork-shaped gratings enabled vortex second-harmonic beam generation with an overall conversion efficiency reaching 1.7%, representing more than an order-of-magnitude improvement over previous approaches. In quartz crystals, cascaded photonic structures allowed simultaneous generation of second- and third-harmonic vortex beams, achieving 3% second-harmonic efficiency and 0.1% third-harmonic efficiency.
“This single-pulse lithography strategy provides a versatile platform for three-dimensional integrated photonics inside transparent dielectrics,” the researchers noted. “By enabling on-demand phase-transition structuring with nanoscale precision, it opens new opportunities for compact, robust, and multifunctional photonic devices fully embedded within all-inorganic crystals.”
Journal
Light Science & Applications
Article Title
Single-pulse lithography of amorphous photonic architectures inside all-inorganic dielectric crystals