Optical security is a promising application of metasurfaces because light has large degrees of freedom in metasurfaces. Although many different structures/materials are proposed for this purpose, the fabrication of dynamic metasurfaces in a straightforward and scalable manner, while maintaining a high security level, remains a significant challenge. Herein, a metasurface consisting of a phase-changing GeSbTe layer and a metal back reflector is presented to space-selectively and dynamically control the infrared emission of the surface by a spatially modulated pulsed laser beam. Unlike conventional laser processes using a focused beam, the employed laser printing is an expanded beam-based parallel process that enables the fabrication of wafer-sized emission patterns. Owing to the multispectral responses of GeSbTe, mutually independent visible and infrared images can be printed in one region. Grayscale emission patterns can also be obtained by gradually modulating the spatial profile of the laser beam, which makes the replication of laser-printed emission patterns extremely difficult. These encouraging features indicate that the presented emissive metasurface has the potential for use as an effective platform for anticounterfeiting.

Engineering the infrared (IR) emissivity of a material or structure is crucial for a variety of fields, including thermal camouflage, radiative cooling, personal thermal management, and optical security. For practical and wide‐spread use, the emitter should possess high mechanical flexibility while maintaining the capabilities of space‐selectively and dynamically controlling its emissivity. In this paper, an optical resonator consisting of a Ge2Sb2Te5 (GST) layer on top of a thin metal reflector stationed on a flexible substrate is presented as an IR emitter that satisfies the aforementioned requirements. A laser‐induced phase change from amorphous to crystalline GST enables dynamic tuning of the local emissivity of the resonator. This study illustrates that although GST is a brittle material, the emitters fabricated on plastic and paper substrates are highly robust against bending up to a radius of curvature of 0.5 cm. Moreover, visible light and IR images can be independently recorded in the same region by employing a spatially modulated laser beam owing to the multispectral properties of GST. The fact that a single emitter can exhibit different visible and IR images is particularly attractive for optical security applications, including anti‐forgery. This feature is experimentally demonstrated using white paper and color‐printed paper.

Multispectral imaging refers to capturing images in different wavelength ranges across the electromagnetic spectrum. Despite the potential impact of multispectral imaging, its widespread use has been limited by the poor spectral selectivity of naturally occurring materials beyond the visible range. In this study, we present a multilayered planar cavity structure to simultaneously record mutually independent visible and infrared (IR) images on solid surfaces. The structure consists of a color control unit (CCU) and an emission control unit (ECU). The visible color of the cavity is controlled by varying the thickness of the CCU, whereas its IR emission is spatially tuned by the laser-induced phase change of a Ge2Sb2Te5 layer embedded in the ECU. Because the CCU comprises only IR lossless layers, its thickness variation has negligible influence on the emission profile. This enables different color and thermal images to be printed in a single structure. The cavity structure can be fabricated on flexible substrates (plastic and paper) as well as rigid bodies. Furthermore, the printed images remain stable against bending. This study shows that the proposed multispectral metasurface is highly promising for use in the field of optical security, such as identification, authentication, and anti-counterfeiting.

Infrared Emitters In article number 2200808, Myeongkyu Lee and co‐workers present a Ge2Sb2Te5 (GST)‐ based infrared emitter that is fabricated on a flexible substrate such as plastic and paper, and its emissivity is space‐selectively controlled using a spatially modulated pulsed laser beam. The multispectral properties of GST enable different visible and thermal images to be simultaneously printed in the same area of the emitter. This provides a promising feature for optical security, including anti‐forgery.

Optical security is a promising application of metasurfaces because light has large degrees of freedom in metasurfaces. Although many different structures/materials have been proposed for this purpose, the fabrication of dynamic metasurfaces in a straightforward and scalable manner while maintaining a high security level remains a significant challenge. Herein, a metasurface consisting of a phase-changing Ge2Sb2Te5 (GST) layer and a thin metal back reflector is presented to space-selectively and dynamically control the infrared emission of the surface by a spatially modulated pulsed laser beam. Unlike conventional laser processes using a focused beam, the employed laser printing is an expanded beam-based parallel process that enables the fabrication of wafer-sized emission patterns. Owing to the multispectral responses of GST, mutually independent visible and infrared images can be printed in one region. Grayscale emission patterns can also be obtained by gradually modulating the spatial profile of the laser beam, which makes the replication of laser-printed emission patterns extremely difficult. These encouraging features are experimentally verified using rigid and flexible substrates, indicating that the presented emissive metasurface has the potential for use as an effective platform for anti-counterfeiting.