Parallel Laser Printing of a Thermal Emission Pattern in a Phase-Change Thin Film Cavity for Infrared Camouflage and Security

Engineering the thermal emission of a material in the long-wavelength infrared (IR) range is applicable to a wide variety of fields, including IR-adaptive camouflage, information encryption, radiative cooling, energy-saving windows, and personal thermal management. Although many different materials or structures have been proposed for these purposes, the position-selective dynamic control of their thermal emission remains a significant challenge. Herein, a laser printing method is presented to spatially tune the thermal emission of a Ge2Sb2Te5 (GST) planar cavity formed on a metal back reflector. Crystallization-induced emission patterns are directly recorded into an amorphous GST film (400 nm thick) in a layer-by-layer fashion, where the crystallization of each layer is patterned using a spatially modulated pulsed laser beam. The proposed parallel laser printing method can produce gradient emission patterns as well as stepwise patterns, enabling the emissivity at a specific position to be tuned from 0.26 to 0.8. This provides a promising platform for IR-adaptive camouflage, which is demonstrated with emissivity-modulated GST emitters. This study also shows that laser-printed emission patterns can be effectively utilized for security applications such as anti-forgery.