Characterization of Laser Beam Shaping Optics Based on Their Ablation Geometry of Thin Films

Abstract

Thin film ablation with pulsed nanosecond lasers can benefit from the use of beam shaping optics to transform the Gaussian beam profile with a circular footprint into a Top-Hat beam profile with a rectangular footprint. In general, the quality of the transformed beam profile depends strongly on the beam alignment of the entire laser system. In particular, the adjustment of the beam shaping element is of upmost importance. For an appropriate alignment of the beam shaper, it is generally necessary to observe the intensity distribution near the focal position of the applied focusing optics. Systems with a low numerical aperture (NA) can commonly be qualified by means of laser beam profilers, such as a charge-coupled device (CCD) camera. However, laser systems for micromachining typically employ focus lenses with a high NA, which generate focal spot sizes of only several microns in diameter. This turns out to be a challenge for common beam profiling measurement systems and complicates the adjustment of the beam shaper strongly. In this contribution, we evaluate the quality of a Top-Hat beam profiling element and its alignment in the working area based on the ablated geometry of single pulse ablation of thin transparent conductive oxides. To determine the best achievable adjustment, we develop a quality index for rectangular laser ablation spots and investigate the influences of different alignment parameters, which can affect the intensity distribution of a Top-Hat laser beam profile.

Mask‐Free Patterning of High‐Conductivity Metal Nanowires in Open Air by Spatially Modulated Femtosecond Laser Pulses

“…The measured intensity profiles matched the simulated ones well (Figures S2 and S3, Supporting Information). Shaped laser beams can also be characterized by the ablation geometry of thin films . The ablation results corresponded well to our simulation results (Figure b).…”

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

“…Their research has shown a significant improvement in holes' quality, especially in drilling brass plates compared to a conventional Gaussian profile. In another investigation, a square top-hat beam was used to scribe 150 nm thin films of indium tin oxide using both refractive and diffractive beam shapers [42,43]. The uniform energy profile of the square top-hat beam allowed for a smaller pulse overlap to be used and this led to nine-fold increase in the scribing speed compared to Gaussian beam processing while achieving a similar quality.…”

Liquid Crystal Pancharatnam–Berry Micro‐Optical Elements for Laser Beam Shaping

“…[1][2][3] Especially, when lasers are used to ablate materials or illuminate photomasks in manufacturing processes, it is often desirable to have a uniform intensity distribution over the cross-section of the beam. [4][5][6] Extensive efforts have been made to develop essential design and fabrication techniques to meet this need. [7,8] In general, designing a beam-shaping system needs to consider two steps, i.e., a phase profile φ(x, y) needed to yield some target intensity profile and an optical element that can generate the desired phase profile.…”