Dr. Craig Zuhlke
Date of this Version
Reicks, A. R. Tailorable Broadband Wide-angle Emissivity Produced Using Femtosecond Laser Surface Processing. MS thesis, 2020. University of Nebraska-Lincoln
Typically, metals are highly reflective in the visible and deep into the infrared (IR) spectrum. Surfaces with high electromagnetic absorption or emission in the IR spectrum are of great interest due to the wide variety of applications, including passive cooling, thermal solar power generation, and thermal management for spacecraft. The emerging advanced manufacturing technique known as femtosecond laser surface processing (FLSP) is used to directly and permanently alter surfaces on the micro- and nanoscales. By modifying the laser parameters, including fluence (between 0.5 and 4.5 j/cm2), pulse count (200 to 8000 pulses), and the atmospheric environment (nitrogen and air), FLSP produces a wide range of structure morphologies with hierarchical micro- and nanoscale surface features. By controlling these laser processing parameters, the hemispherical emissivity of a metal can be tuned, ranging from nearly zero to unity. In this thesis, a broadband near perfect omnidirectional emissive response is demonstrated for the first time on aluminum and stainless steel using FLSP. Theoretical, statistical, and experimental results prove that the broadband omnidirectional increase in emissivity is mainly due to two interdependent causes: the change in the surface morphology and the growth of a thick, redeposited oxide layer. Femtosecond laser surface processing surfaces that have been optimized for high emissivity show little decrease in emissivity at higher angles in addition to broadband operation in the IR spectrum from 7.5 to 14 μm, making FLSP structures ideal for a wide variety of radiative thermal applications.
Advisor: Craig A. Zuhlke