Manchester and the National University of Singapore), have uncovered unusual optical behavior in arsenic trisulfide (As2S3), a crystalline van der Waals semiconductor. Their findings show that this material can be permanently altered by light and even shaped at the nanoscale using simple continuous-wave (CW) light. This approach avoids the need for costly cleanroom fabrication or advanced femtosecond laser systems.
A key concept behind this discovery is the refractive index, which describes how much a material bends or slows light. Materials with higher refractive indices are better at confining and directing light within devices. In certain materials, light can also change this property. This effect, known as photorefractivity, occurs when exposure to light alters the refractive index.
In crystalline As2S3, this response happens even under low-intensity ultraviolet light. The study reports an exceptionally large change in refractive index (up to Δn ≈ 0.3), which exceeds the values typically observed in well-known photorefractive materials such as BaTiO3 or LiNbO3.
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