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Simulations of FLSP surfaces a Simulations of directional and hemispherical emissivity for hemispherical mounds of aluminum with no oxide layer on top. c Simulations of directional and hemispherical emissivity for hemispherical mounds of aluminum with an oxide layer on top. d 3D schematic representing a periodic arrangement of the supercell used to calculate the results in c. b, e Dimensions of the supercell used in the simulations for the emissivity results shown in a and c, respectively. The presented simulations accurately agree with the obtained experimental results.
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It is very challenging to achieve near perfect absorption or emission that is both broadband and omnidirectional while utilizing a scalable fabrication process. Femtosecond laser surface processing is an emerging low-cost and large-scale manufacturing technique used to directly and permanently modify the surface properties of a material. The versat...
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Citations
... The use of femtosecond laser processing to fabricate micro-nano composite structures on substrates has been proposed as a potential solution [40][41][42][43][44][45][46][47][48][49][50][51] . This method can produce structures with both high emissivity and improved stability, offering a promising solution to the challenges mentioned above. ...
The stability and emissivity of the online calibration blackbody used in high-precision infrared remote sensing detectors in extreme environments are the primary limiting factors for their measurement accuracy. Due to the limitations of microstructure size effects, traditional calibration extended area blackbody cannot achieve an optimal balance between emissivity and stability, thus hindering further improvement in infrared remote sensing accuracy. This work proposes a new method that utilize suppressing near-field backscattering to control far-field reflectance. Specifically, through simultaneously reducing backscattering intensity and the backscattering solid angle, the reflectance is significantly reduced to an extremely low limit, which is validated through numerical simulations. Additionally, by combining the femtosecond laser self-convergent processing technique, the spontaneous energy negative feedback mechanism during femtosecond laser processing is utilized to achieve the fabrication of a high emissivity, thermally stable, mechanically stable, and highly uniform extended area blackbody. The blackbody fabricated using this technique can be applied for online calibration in various extreme environments, significantly improving measurement accuracy and service life.
... AM techniques are commonly used to produced textured surfaces for biomedical purposes [13] or to produce hydrophobic surfaces which, similarly to high emissive surfaces, can require microscopic features with high aspect ratios [14]. Pulsed laser ablation has been previously used to increase surface near-unity, broad band emissivity, addressing the limitations of other surface texturizing techniques that may produce narrowband or directional surface emissivity [15]. Aluminium was treated with a femtosecond laser source to produce mound-like microscale features with high aspect ratios, along with a thick oxide layer, both of which are attributed to an increase in hemispherical emissivity. ...
... In our current work, we theoretically demonstrate that femtosecond laser surface processed (FLSP) surfaces can operate as near-perfect omnidirectional absorption or emission substrates [46] with absorption properties extended from mid-IR to visible wavelengths. While such broad absorption spectrum or thermal emission response is ideal for nocturnal radiative cooling devices, it needs to be controlled in an effective way to apply FLSP technology to the counterpart emerging application, i.e., daytime passive radiative cooling. ...
... The final design utilizes Brewster angle transmission to achieve broadband directional thermal emission limited to TM polarization. Note that the emissivity of the FLSP surface is significantly higher and more omnidirectional than just simple coating a metallic mirror with alumina, as was demonstrated in our previous work [46]. ...
... By controlling laser parameters such as the number of pulses, pulse duration, and laser fluence, many different types of periodic or quasi-periodic structures can be produced usually on metallic surfaces using a femtosecond laser system [47][48][49]. We have previously presented experimental results from FLSP on an Al surface that produced mounds of Al covered by a thick layer of aluminum oxide (Al 2 O 3 ) [46]. The absorptance of the aluminum FLSP surface structure is near perfect in the mid-IR, as was theoretically verified and experimentally measured in our previous work [46]. ...
Development of methods to control the directional and spectral characteristics of thermal radiation from metallic surfaces is a critical factor enabling many important thermal management applications. In this paper, we study the thermal emission properties of functionalized aluminum surfaces produced through femtosecond laser surface processing (FLSP). These types of surfaces have recently been found to exhibit near-unity broadband omnidirectional emissivity. However, their ultrabroadband absorption response includes visible and near-infrared (IR) radiation, in addition to the mid-IR range, which limits their use as daytime passive radiative cooling devices. Here, we present ways to solve this problem by demonstrating a new, to our knowledge, design that uses a dielectric Bragg visible light reflector to accurately control the thermal emission spectra of the FLSP surface with the goal of achieving high-performance daytime radiative cooling operation. In addition, we propose other designs based on dielectric multilayer structures to further tailor and control the spectra and thermal emission angles of the FLSP surfaces leading to narrowband and broadband directional thermal radiation. The presented photonic engineering approach combined with FLSP structures will be beneficial to various emerging applications, such as radiative cooling, thermal sensing, and thermophotovoltaics.
... In our current work, we theoretically demonstrate that femtosecond laser surface processed (FLSP) surfaces can operate as near perfect omnidirectional absorption or emission substrates [46] with absorption properties extended from mid-IR to visible wavelengths. While such broad absorption spectrum or thermal emission response is ideal for nocturnal radiative cooling devices, it needs to be controlled in an effective way to apply FLSP technology to the counterpart emerging application, i.e., daytime passive radiative cooling. ...
... The final design utilizes Brewster angle transmission to achieve broadband directional thermal emission limited to TM polarization. Note that the emissivity of the FLSP surface is significantly higher and more omnidirectional than just simple coating a metallic mirror with alumina, as was demonstrated in our previous work [46]. ...
... By controlling laser parameters such as the number of pulses, pulse duration, and laser fluence many different types of periodic or quasi-periodic structures can be produced usually on metallic surfaces using a femtosecond laser system [47][48][49][50]. We have previously presented experimental results from FLSP on an Al surface that produced mounds of Al covered by a thick layer of aluminum oxide (Al2O3) [46]. The absorptance of the aluminum FLSP surface structure is near perfect in the mid-IR, as was theoretically verified and experimentally measured in our previous work [46]. ...
Development of methods to control the directional and spectral characteristics of thermal radiation from metallic surfaces is a critical factor enabling many important thermal management applications. In this paper, we study the thermal emission properties of functionalized aluminum surfaces produced through femtosecond laser surface processing (FLSP). These types of surfaces have recently been found to exhibit near-unity broadband omnidirectional emissivity. However, their ultrabroadband absorption response includes visible and near-infrared (IR) radiation, in addition to the mid-IR range, which limits their use as daytime passive radiative cooling devices. Here, we present ways to solve this problem by demonstrating a new design that uses a dielectric Bragg visible light reflector to accurately control the thermal emission spectra of the FLSP surface with the goal of achieving high performance daytime radiative cooling operation. In addition, we propose other designs based on dielectric multilayer structures to further tailor and control the spectra and thermal emission angles of the FLSP surfaces leading to narrowband and broadband directional thermal radiation. The presented photonic engineering approach combined with FLSP structures will be beneficial to various emerging applications, such as radiative cooling, thermal sensing, and thermophotovoltaics.
... [5][6] and have been studied for blackening applications, notably in the thermal infrared using an index matching with an oxide layer. 7 It is straightforward to lower the specular reflectance with ultrafast texturing. However, while the specular reflectance is significantly lower than the unprocessed surface, but the diffuse reflectance is generally higher due scatter from microscale features. ...
... Femtosecond laser surface processing (FLSP) is a surface functionalization technique that is used to create micro/nanostructures on a wide range of materials, including metals and semiconductors. Surface roughening is beneficial for a number of applications including enhancing heat transfer [1][2][3][4][5], controlling wetting properties [6][7][8][9][10][11][12][13][14], and controlling the absorption/reflectivity of surfaces [15][16][17][18][19]. There is specific interest in microstructuring copper due to its thermal and antibacterial properties [2,20,21]. ...
Femtosecond lasers can be used to create self-organized micro/nanostructures on the surface of most materials. However, on copper, these structures require significantly higher laser fluence when compared to other metals. We report a method to create self-organized structures on copper by clamping a foil of stainless steel on the copper surface prior to laser processing. All samples reported are processed using a peak fluence of 2.71 J/cm 2 , which is below the fluence threshold for self-organized micro/nanostructure formation on copper. When stainless steel is layered on copper, structures are created that consist of both stainless steel and copper at pulse counts of 998 and 1,197. With increased pulse count, the thickness of the stainless steel layer decreases. For pulse counts of 1,497 and higher, the permanent structures are completely composed of copper. Using these same parameters, but without the stainless steel foil on the copper, the laser processing formed agglomerations of nanoparticles on the surface regardless of pulse count. The structure morphology and chemistry of the surface features are characterized with surface and subsurface analysis to study the material make-up of the structures and investigate the pulse count necessary to fully remove the stainless steel, leaving a structured copper surface.
... It was proven that aluminum surfaces could emit light in an almost pristine, broadband, and omni-directional fashion by the manipulation of the following parameters: pulse count, fluence, and ambient environment. This process yields functionalized metallic surfaces ideal for cutting-edge applications such as passive radiative cooling [39]. ...
In the present work, the integration of femtosecond laser surface processing (FLSP) with copper
hydroxide on hybrid surfaces was examined. The goal was to determine the impact on pool boiling
enhancement. The samples for the investigation were fabricated by first functionalizing with
FLSP, and the process was then followed by citric acid cleaning (CAC) to eliminate the oxides
generated on the copper surface during the FLSP process. After the citric acid cleaning, the
samples were immersed in ethanol and subjected to an ultrasonic bath for 25 minutes. This step
was performed to eliminate any residual citric acid and loose particles. Copper hydroxide
nanoneedles (NN) were then synthesized on the FLSP surface. Lastly, some selected samples were
heat-treated (HT) at 200oC for 30 minutes to ensure the nanoneedles were secured in place even
after several pool boiling runs. The study showed that heat-treated nanoneedle surfaces offer
enhanced pool boiling performance compared to untreated ones, and the results are consistent and
repeatable. Sample E (FLSP+CAC+NN+HT) exhibited a critical Heat Flux (CHF) of 116.1 W/cm2
and a heat transfer coefficient (HTC) of 50.5 kW/m2
-K which outperformed sample C
(FLSP+CAC+NN) that exhibited a CHF of 100 W/cm2 at an HTC of 45.2 kW/m2
-K. It was
observed that the inclusion of nanoneedles resulted in diminished performance when compared to
a polished copper surface. The decline was attributed to the decomposition of
copper hydroxide into copper oxide, consequently introducing insulating material to the surface.
Boiling inversion was observed on all tested nanoneedle surfaces.
... However, it cannot be excluded that the low degree of correlation could be a consequence of the flaws of EDX measurements on non-flat non-homogenous surfaces. Nonetheless, the higher surface oxidation on samples fabricated with larger cumulated fluences (C4-C6, P4-P6) is likely to increase the emissivity of the surfaces and could thereby increase heat transfer through radiative cooling [23]. ...
With the increasing processing power of micro-electronic components and increasing spatial limitations, ensuring sufficient heat dissipation has become a crucial task. This work presents a microscopic approach to increasing the surface area through periodic surface structures. Microstructures with a periodic distance of 8.5 µm are fabricated via Direct Laser Interference Patterning (DLIP) on stainless steel plates with a nanosecond-pulsed infrared laser and are characterized by their developed interfacial area ratio. The optimal structuring parameters for increasing the surface area were investigated, reaching peak-to-valley depths up to 12.8 µm and increasing surface area by up to 394%. Heat dissipation in a natural convection environment was estimated by measuring the output voltage of a Peltier element mounted between a hot plate and a textured sample. The resulting increase in output voltage compared to an unstructured sample was correlated to the structure depth and developed interfacial area ratio, finding a maximum increase of 51.4%. Moreover, it was shown that the output voltage correlated well with the structure depth and surface area.
... Owing to its high precision, fast processing, excellent repeatability, and low-cost, the FLSP method has received substantial attention regarding applications in different fields ranging from nanotechnology and medicine to engineering and science. [1][2][3][4][5][6][7][8] Due to the ultrashort femtosecond laser pulses used, FLSP leads to minimal thermal damage to the material outside the laser focal spot making it desirable property to construct different surface morphologies on temperature sensitive delicate structures. [9][10][11] In previous works, during FLSP on metals, it has been demonstrated that low laser fluence illumination can lead to laser induced periodic surface structures (LIPSS). ...
Femtosecond laser surface processing (FLSP) is an emerging fabrication technique to efficiently control the surface morphology of many types of materials including metals. However, the theoretical understanding of the FLSP formation dynamics is not a trivial task, since it involves the interaction of various physical processes (electromagnetic, thermal, fluid dynamics) and remains relatively unexplored. In this work, we tackle this problem and present rigorous theoretical results relevant to low-fluence FLSP that accurately match the outcomes of an experimental campaign focused on the formation dynamics of laser induced periodic surface structures (LIPSS) on stainless steel. More specifically, the topology and maximum depth of LIPSS trenches are theoretically and experimentally investigated as a function of the number of laser pulses. Moreover, precise LIPSS morphology measurements are performed using atomic force microscopy (AFM). The proposed comprehensive simulation study is based on two-temperature model (TTM) non-equilibrium thermal simulations coupled with fluid dynamic computations to capture the melting metal phase occurring during FLSP. Our rigorous simulation results are found to be in excellent agreement with the AFM measurements. The presented theoretical framework to model FLSP under low-fluence femtosecond laser pulses will be beneficial to various emerging applications of LIPSS on metallic surfaces, such as cooling high-powered laser diodes and controlling the thermal emission or absorption of metals.
... Thermal radiation is a fundamental natural phenomenon where light is spontaneously emitted from an object due to increased heating [1,2]. The photonic engineering of thermal radiation has enabled exciting and novel applications such as passive radiative cooling [3][4][5] and thermophotovoltaics [6,7]. ...
... From the reflectance, the absorptance A(λ, θ ) and emissivity E (λ, θ ) can be computed by using Eqs. (2) and (3) [23], ...
Nonreciprocal thermal emission is a cutting-edge technology that enables fundamental control over thermal radiation and has exciting applications in thermal energy harvesting. However, thus far one of the foremost challenges is making nonreciprocal emission operate over a broad wavelength range and for multiple angles. In this work, we solve this outstanding problem by proposing three different types of structures that always utilize only one Weyl semimetal (WSM) thin film combined with one or two additional dielectric or metallic layers and terminated by a metallic substrate. First, a tradeoff relationship between the magnitude and bandwidth of the thermal nonreciprocity contrast is established based on the thickness of the WSM film. Then, the bandwidth broadening effect is demonstrated via the insertion of a dielectric spacer layer that can also be fine-tuned by varying its thickness. Finally, further control on the resulting strong nonreciprocal thermal radiation is demonstrated by the addition of a thin metallic layer in the proposed few layer designs. The presented composite structures work for a broad frequency range and for multiple emission angles, resulting in highly advantageous properties for various nonreciprocal thermal radiation applications. Moreover, the proposed designs do not require any patterning and can be experimentally realized by simple deposition fabrication methods. They are expected to aid in the creation of broadband nonreciprocal thermal emitters that can find applications in new energy harvesting devices.
