We demonstrated laser-induced broadband emitters (LIBEs) with spectral emissivity higher than 0.96 from 0.3 um to 15 um wavelength to increase thermal radiative energy transport. Localized material removal induced by ultrafast femtosecond laser irradiation results in the hierarchical formation of microstructures decorated with micro-/nano- particles, leading to an exceptional enhancement in a spectral absorptivity on different types of substrates. Finite-difference time-domain simulations validated the effects of surface topology on the experimentally measured absorptivity. Moreover, LIBEs maintain their enhanced spectral absorptivity of 0.92 after heating at elevated temperatures for over 100 hours. Our results provide new insights into the use of ultrafast laser-matter interactions in cutting-edge energy harvesting and thermal management applications.
In this work, we study the ablation dynamics of copper (Cu) induced by single fs pulse and fs GHz bursts using in situ multimodal diagnostics; time-resolved scattering imaging, emission imaging, and optical emission spectroscopy. Multimodal probing techniques reveal that fs GHz bursts rapidly remove molten liquid Cu from the irradiated spot due to the recoil pressure exerted by following fs pulses. Material ejection stops after burst irradiation due to the limited amount of remnant matter, combined with the suppressed heat conduction into the target material. Our work provides insights into the complex ablation mechanisms of GHz fs bursts, which are critical in selecting optimal laser conditions in cross-cutting processing and micro/nano-fabrication applications.
To examine the ablation dynamics of silver thin films by femtosecond laser, we experimentally investigate the plume evolution and behavior of ejected nanoparticles (NPs) via emission and scattering spectroscopy measurements under background pressures of 760 torr, 5 torr, 5 x 10-3 torr, to 3 x 10-5 torr. The emission spectroscopy experiments show that the propagation of the ablated plume is affected by ambient pressure. The higher the pressure, the more the propagation of the plasma is suppressed. Under higher vacuum, the lifetime of plasma is shorter due to diminished collisions with background molecules. The evolution of plasma lasts more than 200 ns under 760 torr while it does not exceed 200 ns under high vacuum (3 x 10-5 torr). Through the scattering measurements, the average propagation speed of NPs is 200 m/s under 3 x 10-5 torr, 190 m/s under 5 x 10-3 torr, 155 m/s under 5 torr, and 120 m/s under 760 torr. The ejected nanoparticles from the periphery of the ablated spot exhibit oblique trajectories because of the exerted recoil pressure at the spot center region that is subject to high incident energy densities.
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