Spectral absorption control of femtosecond laser-treated metals and application in solar-thermal devices

Materials processing: laser modified metals Femtosecond-laser processing of materials has many potential applications including high-efficiency incandescent lamps and solar-thermal receivers. A longstanding challenge is the ability to control the emerging properties of the treated surfaces. A research team at Chunlei Guo's lab from the Institute of Optics at the University of Rochester showed that the spectral absorption properties of treated metals can be controlled systematically by controlling the laser processing parameters. They showed that the formed structures act as interacting nano-antennas which absorbs light based on the excitation of electromagnetic resonances. As a direct application, they converted a Tungsten surface to a selective solar-absorber and used it to operate a thermoelectric generator which resulted in a 130% increase in efficiency compared to an untreated tungsten receiver. Direct femtosecond (fs) laser processing is a maskless fabrication technique that can effectively modify the optical, electrical, mechanical, and tribological properties of materials for a wide range of potential applications. However, the eventual implementation of fs-laser-treated surfaces in actual devices remains challenging because it is difficult to precisely control the surface properties. Previous studies of the morphological control of fs-laser-processed surfaces mostly focused on enhancing the uniformity of periodic microstructures. Here, guided by the plasmon hybridisation model, we control the morphology of surface nanostructures to obtain more control over spectral light absorption. We experimentally demonstrate spectral control of a variety of metals [copper (Cu), aluminium (Al), steel and tungsten (W)], resulting in the creation of broadband light absorbers and selective solar absorbers (SSAs). For the first time, we demonstrate that fs-laser-produced surfaces can be used as high-temperature SSAs. We show that a tungsten selective solar absorber (W-SSA) exhibits excellent performance as a high-temperature solar receiver. When integrated into a solar thermoelectric generation (TEG) device, W-SSA provides a 130% increase in solar TEG efficiency compared to untreated W, which is commonly used as an intrinsic selective light absorber.