Discovery of Novel Optical Properties in a Van der Waals Crystal

Scientists from the XPANCEO Emerging Technologies Research Center, in collaboration with Nobel Laureate Professor Konstantin Novoselov, have discovered that the van der Waals semiconductor crystalline arsenic trisulfide (As₂S₃) possesses remarkable and useful optical properties.

The discovery of new functional materials, particularly within the unique family of van der Waals crystals, is the fundamental engine for moving the entire field of photonics forward.

— Valentyn Volkov, Founder and CTO at XPANCEO

The research demonstrates that this material can be permanently modified and physically sculpted at the nanoscale using simple continuous-wave light. This process bypasses the need for complex cleanroom lithography or expensive femtosecond pulsed lasers.

Key Material Properties

Crystalline As₂S₃ shows a light-induced refractive-index change of up to Δn ≈ 0.3 under low-intensity UV illumination. This change is notably larger than values typically cited for classic photorefractive crystals like barium titanate (BaTiO₃) or lithium niobate (LiNbO₃).

Furthermore, the material can physically expand by up to 5% under light exposure, enabling the direct sculpting of three-dimensional optical elements.

Demonstrations of Precision and Capability

To showcase the technique's precision, researchers used a standard laser to create a microscopic portrait of Albert Einstein on a material flake. The portrait featured 700-nanometer spacing between individual points.

In separate tests, the method achieved approximately 50,000 dots per inch, which corresponds to a spacing of just 500 nanometers between points. The written patterns show strong optical contrast directly resulting from the light-driven refractive index change.

Potential Applications

The unique properties of this material open the door to a wide range of potential applications:

• Optical Hardware: Creating optical structures for telecommunications equipment.
• Sensors and Imaging: Fabricating diffractive elements for advanced sensors and imaging systems.
• Security Features: Developing hologram-like optics and extremely fine "optical fingerprints" for anti-counterfeiting and product traceability.
• Augmented Reality: Contributing to the creation of ultra-wide field-of-view waveguides for AR glasses and smart contact lenses.
• Advanced Photonics: Serving as a candidate material for next-generation photonic circuits and highly sensitive nanoscale sensors.

Valentyn Volkov of XPANCEO emphasized the significance of the find, adding that identifying natural crystals with this sensitivity provides building blocks for technology driven by light rather than electricity.