Development and Validation of a Calculation Routine for the Precise Determination of Pulse Overlap and Accumulated Fluence in Pulsed Laser Surface Treatment
Abstract:In laser material processing, a variety of parameters like pulse fluence, total dose, step size, and pulse-to-pulse overlap are used to define and compare laser processes. Of these parameters, the pulse-to-pulse overlap can be the hardest to access as it is not implemented directly but instead depends on the spot diameter, its shape, and the respective scanning path that is used to cover the surface. This article shows that existing calculation routes overestimate the actual overlap by up to 21%. A novel calcu… Show more
“…Depending on the used pulse-to-pulse distance as well as the laser beam diameter 2 ω 0 , different pulse-to-pulse overlaps can be achieved as described by the Eq. ( 1 ) 41 : Figure 1 ( a ) DLIP configuration and ( b ) ITO patterning strategy. …”
A route to increase the efficiency of thin film solar cells is improving the light-trapping capacity by texturing the top Transparent Conductive Oxide (TCO) so that the sunlight reaching the solar absorber scatters into multiple directions. In this study, Indium Tin Oxide (ITO) thin films are treated by infrared sub-picosecond Direct Laser Interference Patterning (DLIP) to modify the surface topography. Surface analysis by scanning electron microscopy and confocal microscopy reveals the presence of periodic microchannels with a spatial period of 5 µm and an average height between 15 and 450 nm decorated with Laser-Induced Periodic Surface Structures (LIPSS) in the direction parallel to the microchannels. A relative increase in the average total and diffuse optical transmittances up to 10.7% and 1900%, respectively, was obtained in the 400–1000 nm spectral range as an outcome of the interaction of white light with the generated micro- and nanostructures. The estimation of Haacke’s figure of merit suggests that the surface modification of ITO with fluence levels near the ablation threshold might enhance the performance of solar cells that employ ITO as a front electrode.
“…Depending on the used pulse-to-pulse distance as well as the laser beam diameter 2 ω 0 , different pulse-to-pulse overlaps can be achieved as described by the Eq. ( 1 ) 41 : Figure 1 ( a ) DLIP configuration and ( b ) ITO patterning strategy. …”
A route to increase the efficiency of thin film solar cells is improving the light-trapping capacity by texturing the top Transparent Conductive Oxide (TCO) so that the sunlight reaching the solar absorber scatters into multiple directions. In this study, Indium Tin Oxide (ITO) thin films are treated by infrared sub-picosecond Direct Laser Interference Patterning (DLIP) to modify the surface topography. Surface analysis by scanning electron microscopy and confocal microscopy reveals the presence of periodic microchannels with a spatial period of 5 µm and an average height between 15 and 450 nm decorated with Laser-Induced Periodic Surface Structures (LIPSS) in the direction parallel to the microchannels. A relative increase in the average total and diffuse optical transmittances up to 10.7% and 1900%, respectively, was obtained in the 400–1000 nm spectral range as an outcome of the interaction of white light with the generated micro- and nanostructures. The estimation of Haacke’s figure of merit suggests that the surface modification of ITO with fluence levels near the ablation threshold might enhance the performance of solar cells that employ ITO as a front electrode.
“…The employed patterning strategy is illustrated in Figure 1b. Depending on the used pulse-to-pulse distance 𝑝 d as well as the laser beam diameter 2 0 , different pulse-to-pulse overlaps (𝑂𝑉) can be achieved as described by the equation (1) 41 :…”
A route to increase the efficiency of thin film solar cells is improving the light-trapping capacity by texturing the top Transparent Conductive Oxide (TCO) so that the sunlight reaching the solar absorber scatters into multiple directions. In this study, Indium Tin Oxide (ITO) thin films are treated by infrared sub-picosecond Direct Laser Interference Patterning (DLIP) to modify the surface topography. Surface analysis by scanning electron microscopy and confocal microscopy reveals the presence of periodic microchannels with a spatial period of 5 m and an average height between 15 and 450 nm decorated with Laser-Induced Periodic Surface Structures (LIPSS) in the direction parallel to the microchannels. A relative increase in the average total and diffuse optical transmittances up to 10.7% and 1,900%, respectively, was obtained in the 400-1,000 nm spectral range as an outcome of the interaction of white light with the generated micro- and nanostructures. The estimation of Haacke’s figure of merit suggests that the surface modification of ITO with fluence levels near the ablation threshold might enhance the performance of solar cells that employ ITO as a front electrode.
“…Wire‐cut electrical discharge machining (EDM) was used to cut 5×5 mm samples out of a 1 mm thick titanium sheet (HMW Hanauer GmbH; 99.995 wt.%). The resulting samples were mirror‐polished following a multi‐step routine described in detail in a previous work [49] …”
Section: Experimental Section/methodsmentioning
confidence: 99%
“…The process parameters required to obtain the desired sample characteristics were calculated using a routine developed and reported in previous work. [49] While the line patterns were produced in a single process step with two beams, for the cross patterns two perpendicular line patterns each with half the total number of pulses were overlapped. The surfaces without an interference pattern were produced by blocking all but one beam and scanning the surface with a single beam.…”
Section: Sample Preparationmentioning
confidence: 99%
“…The resulting samples were mirror-polished following a multi-step routine described in detail in a previous work. [49] After cleaning the samples in ethanol, the laser patterning was performed using an Edgewave px picosecond laser with a pulse width of 12 ps, a wavelength of 532 nm, a repetition rate of 100 kHz and a maximum average power of 10 W. In direct laser interference patterning a single laser beam is split into coherent sub-beams that are then brought to interference on the sample surface. The resulting interference pattern depends only on the laser's wavelength, its polarization, and the angle between the beams while the general pattern type can be adjusted by the number of beams used.…”
State of the art approaches to produce photocatalytic surfaces generally require multiple processing steps to achieve highly active surfaces. Following recent trends to facilitate the production of active surfaces, this work presents a single‐step method to create porous photocatalytic surfaces via direct laser interference patterning (DLIP) of a titanium substrate with pulses in the picosecond range. The resulting surfaces contain a variety of titanium oxides while both their composition and morphology can be controlled through the laser process parameters. This makes it possible to tailor these surfaces for specific applications such as antimicrobial surfaces, implant materials or water treatment. Surface characterization was executed by applying scanning electron microscopy complemented by focused ion beam cross‐sectioning and energy dispersive X‐ray spectroscopy as well as gracing incidence X‐ray diffractometry. The photocatalytic activity achieved by different laser parameters is assessed by methylene blue degradation under UV‐A light. As DLIP is already established in industrial applications, this approach could greatly facilitate the use of photocatalytic surfaces for water treatment or medical applications, as it does not require nanoparticle synthesis or additional coating steps.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
