We investigate cutting of transparent materials using ultra short laser pulses with pulse durations in the sub to a few ps regime. All compared methods base on nonlinear absorption including ablation cutting and cleaving or selective etching supported by laser induced modification inside the bulk material. For most of the experiments samples of hardened glass (Corning Gorilla®) with thickness up to 700 µm were used, ablation cutting of sapphire is presented additionally. Absorption and modification inside the volume is analyzed in detail, aiming for tailored modifications. Besides optical microscopy a pump probe setup was used. We show results of time resolved absorption measurements of 6 ps pulses focused into the volume. We observe shielding due to the interaction region and accumulation effects influencing the modifications. First results on inscribing and cutting by using beam shaping indicate the importance of tailoring the shape and arrangement of the pulses temporally and spatially. The results presented for the different cutting methods supports an assessment of the individual potential and a selection of the applicable method based on the requirements
Ultrashort laser pulses allow for the in-volume processing of glass through non-linear absorption, resulting in permanent material changes and the generation of internal stress. Across the manifold potential applications of this technology, process optimization requires a detailed understanding of the laser-matter interaction. Of particular relevance are the deposition of energy inside the material and the subsequent relaxation processes. In this paper, we investigate the spatio-temporal evolution of free carriers, energy transfer, and the resulting permanent modifications in the volume of glass during and after exposure to femtosecond and picosecond pulses. For this purpose, we employ time-resolved microscopy in order to obtain shadowgraphic and interferometric images that allow relating the transient distributions to the refractive index change profile. Whereas the plasma generation time is given by the pulse duration, the thermal dynamics occur over several microseconds. Among the most notable features is the emergence of a pressure wave due to the sudden increase of temperature and pressure within the interaction volume. We show how the structure of the modifications, including material disruptions as well as local defects, can be directly influenced by a judicious choice of pulse duration, pulse energy, and focus geometry.
We demonstrate time-resolved tomography with 200 fs resolution for the three-dimensional analysis of the non-linear dynamics of ultrafast laser-matter interaction inside the volume of transparent materials. We reconstruct as an example the three-dimensional spatial distribution of the transient extinction coefficient induced by focusing higher-order Bessel-Gaussian-beams into Gorilla glass. This approach can be employed to gaseous, liquid and transparent solid state matter which interact with laser light.
Ultrashort laser pulses allow for in-volume processing of glass through non-linear absorption. This results in permanent material changes, largely independent of the processed glass, and it is of particular relevance for cleaving applications. In this paper, a laser with a wavelength of 1030 nm, pulse duration of 19 ps, repetition rate of 10 kHz, and burst regime consisting of either four or eight pulses, with an intra-burst pulse separation of 12.5 ns, is used. Subsequently, a Gaussian-Bessel focal line is generated in a fused silica substrate with the aid of an axicon configuration. We show how the structure of the modifications, including the length of material disruptions and affected zones, can be directly influenced by a reasonable choice of focus geometry, pulse energy, and burst regime. We achieve single-shot modifications with 2 μm in diameter and 7.6 mm in length, exceeding an aspect ratio of 1:3800. Furthermore, a maximum length of 10.8 mm could be achieved with a single shot.
A new approach for generating long‐distance self‐healing Bessel beams, which is based on a ring‐shaped (annular) lens and a spherical lens in 4f‐configuration, is reported. With this, diffraction‐free light evolution of a zeroth order Bessel beam over several meters is shown and available scaling opportunities that surpass current technologies by far are discussed. Furthermore, it is demonstrated how this setup can be adapted to create Bessel beam superpositions, realizing the longest ever reported optical conveyor beam and helicon beam, respectively. Last, the self‐healing capabilities of the beams are tested against strong opaque and non‐opaque scatterers, which again emphasizes the great potential of this new method.
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