Femtosecond laser process enables switchable photothermal and cooling metal surfaces

A Shanghai Jiao Tong University team published a new Opto-Electronic Science study on a femtosecond laser plus thermal annealing method that turns metal surfaces into switchable photothermal and radiative-cooling interfaces. The approach works across several transition metals and could support day-night thermal management and photo-thermoelectric generation.

Why it matters: - The new processing paradigm could make metal-based thermal regulation more durable and more adaptable than oxide-polymer cooling coatings. - The work targets interfacial heat management for harsh environments, where surfaces need to switch between absorbing heat and shedding it. - The method may support 24-hour photo-thermoelectric generation by pairing daytime photothermal heating with nighttime radiative cooling.

What happened: - Researchers at Shanghai Jiao Tong University published a study in Opto-Electronic Science on a femtosecond laser-based “Janus-material/function” processing paradigm for photothermal and radiative cooling modulation. - The team used femtosecond laser micro/nano-machining followed by 600°C thermal oxidation treatment to create metal-based Janus thermal-regulation interfaces. - The study was led by Associate Professor Dongshi Zhang and Professor Zhuguo Li, with Dr. Jianing Liao as first author.

The details: - On tungsten, femtosecond laser processing synthesized and deposited black WO3-x nanomaterials on the metal surface. - Optimized thermal annealing converted the black tungsten oxide interface into a white WO3-x surface. - The metal substrate and interfacial oxides produced a Janus system because of their different thermal conductivity and infrared emissivity. - Under 1-sun irradiation, the photothermal interface raised tungsten temperature by 9°C, while the radiative-cooling interface lowered it by 2°C. - The process enabled monolithic fabrication of tungsten-based black/white interfaces and single-sided, double-sided, and integrated single/double-sided Janus PT/RC structures. - The team said the approach can also be extended to colorful radiative-cooling interfaces. - The method was verified on Ta, Mo, and Nb substrates. - A Ti-based PT interface retained its black color after annealing at 600°C for two hours, showing unusually strong thermal-oxidation resistance. - The black and white tungsten interfaces withstood thermal oxidation at 100°C and 200°C for four hours. - The interfaces also resisted hand shaking and tape scratching. - The publication title is “Femtosecond laser based ‘Janus-material/function’ processing paradigm for photothermal and radiative cooling modulation.” - The paper is indexed as Opto-Electron Sci 5, 260023 (2026) with DOI 10.29026/oes.2026.260023.

Between the lines: - The advance is less about a single coating and more about a fabrication platform for switching surface function by material choice, laser texturing, and annealing. - The use of metals such as tungsten, tantalum, molybdenum, niobium, and titanium suggests a broader design space than common polymer-based cooling materials. - The resistance tests point to a practical step toward surfaces that can survive handling and heat exposure, not just lab-only demonstrations.

What's next: - The authors indicate the approach could be expanded to gradient thermal-regulation materials and additional metal systems. - Further development could focus on scaling the process for real devices and broader environmental testing. - The team’s next applications appear aimed at optical and photothermal modulation, metamaterials, and multifunctional thermal-regulation interfaces.

The bottom line: - The study lays out a laser-and-anneal route for making metal surfaces that can flip between heating and cooling functions, with durability that may make the approach useful outside the lab.