Researchers from the XPANCEO Emerging Technologies Research Center, in collaboration with Nobel Laureate Prof. Konstantin Novoselov, have discovered that the crystalline van der Waals semiconductor arsenic trisulfide (As2S3) exhibits a remarkably strong photorefractive effect. This means low-intensity ultraviolet light can permanently alter its refractive index - by up to Δn ≈ 0.3, a change that surpasses those in classic materials like BaTiO3 or LiNbO3 - without needing expensive cleanrooms or fancy femtosecond lasers.
This property allows optical functions to be directly 'written' into the material, a handy trick for creating the tiny structures in telecom systems, compact optical components for sensors, and hologram-like features for security. The effect is so potent at the nanoscale that it can create unique, hard-to-replicate 'optical fingerprints,' ideal for anti-counterfeiting.
To showcase this precision, the team used a standard laser to etch a microscopic portrait of Albert Einstein onto a thin piece of As2S3, with points spaced a mere 700 nanometers apart. They've even pushed the resolution to ~50,000 dots per inch (about 500 nanometers between points), producing patterns with strong optical contrast thanks to the light-induced changes.
Beyond just patterning, exposure to light makes As2S3 physically expand by up to 5%, enabling the direct formation of optical structures like microlenses and diffraction gratings on its surface. This is crucial for developing components like wide field-of-view waveguides for augmented reality glasses and smart contact lenses.
Valentyn Volkov, Founder and CTO at XPANCEO, noted that discovering such sensitive natural crystals provides the 'essential building blocks' for a new generation of light-driven technology, moving photonics forward from its electrical roots. The material's responsiveness also makes it promising for photonic circuits and nanoscale sensors, marking a significant step in manipulating light for next-gen tech.