Effects of Top-hat Laser Beam Processing and Scanning Strategies in Laser Micro-Structuring

Abstract

The uniform energy distribution of top-hat laser beams is a very attractive property that can offer some advantages compared to Gaussian beams. Especially, the desired intensity distribution can be achieved at the laser spot through energy redistribution across the beam spatial profile and, thus, to minimize and even eliminate some inherent shortcomings in laser micro-processing. This paper reports an empirical study that investigates the effects of top-hat beam processing in micro-structuring and compares the results with those obtainable with a conventional Gaussian beam. In particular, a refractive field mapping beam shaper was used to obtain a top-hat profile and the effects of different scanning strategies, pulse energy settings, and accumulated fluence, i.e., hatch and pulse distances, were investigated. In general, the top-hat laser processing led to improvements in surface and structuring quality. Especially, the taper angle was reduced while the surface roughness and edge definition were also improved compared to structures produced with Gaussian beams. A further decrease of the taper angle was achieved by combining hatching with some outlining beam passes. The scanning strategies with only outlining beam passes led to very high ablation rates but in expense of structuring quality. Improvements in surface roughness were obtained with a wide range of pulse energies and pulse and hatch distances when top-hat laser processing was used.

Micro-Hole Generation by High-Energy Pulsed Bessel Beams in Different Transparent Materials

“…The laser beam shape and the beam propagation features also play a crucial role in determining the hole quality, and research continues to be carried out for the optimization of the system performance such as speed, throughput, sidewall taper, or symmetry [6][7][8]. In particular, an important advance in ultrafast laser processing has been through the development of "non-diffracting" beams, which enable overcoming many of the difficulties usually encountered with standard Gaussian beam focusing in materials [9,10].…”

Thermochemical Laser-Induced Periodic Surface Structures Formation by Femtosecond Laser on Hf Thin Films in Air and Vacuum

“…Thus, the results obtained show that hafnium is a promising material for the high-throughput formation of TLIPSS with a high structures regularity. It is likely that the quality of the formed structures can be further improved by using a top-hat beam with a uniform power distribution within the focal spot [32]. As shown in Figure 6, TLIPSS formed on hafnium films in air, within the used ranges of power and scanning speed, have a high degree of ordering (DLOA δθ < 4°).…”

“…Thus, the results obtained show that hafnium is a promising material for the high-throughput formation of TLIPSS with a high structures regularity. It is likely that the quality of the formed structures can be further improved by using a top-hat beam with a uniform power distribution within the focal spot [32]. Since the formation of TLIPSS requires the presence of oxygen for the oxidation reaction, to determine the influence of the ambient oxygen concentration on TLIPSS formation, experiments were also carried out in a low vacuum (residual air pressure of 4 Torr).…”

Doughnut-Shaped and Top Hat Solar Laser Beams Numerical Analysis

“…The irradiance cross-section of Gaussian beams, however, gradually decreases from the center to the periphery of the laser spot so that a portion of the laser beam profile may not have enough irradiance for the given application. Moreover, this wasted energy can even damage surrounding areas outside of the target, extending the heat-affected zones [12]. The simplest way to address this issue is to convert the Gaussian energy distribution into a more uniform profile, such as the top hat beam profile [13].…”

“…Experimentally, it is not possible to obtain such an idyllic top hat beam since it would require an infinite spatial frequency spectrum [13], but several approximations can be made, namely Fermi-Dirac, super-Lorentzian, super-Gaussian, flattened Gaussian beams, and multi-Gaussian beams [29,30]. Compared to Gaussian beams, a more flattened beam profile can generate cleaner cuts and sharper edges, resulting in increased accuracy for high-demand applications [31], including laser micromachining [12], precise materials processing [32], direct laser interference patterning [33] and precise laser surgery [34]. However, generating a top hat profile raises the system cost and complexity while its output power is significantly reduced.…”