J. Eur. Opt. Society-Rapid Publ. 21, 22( 2025) 215
qualities [ 5, 6, 9, 14 ]. This is accompanied by efforts to develop new machining processes or to optimize existing processes. One approach is the use of hybrid manufacturing processes, such as ultrasonic-assisted grinding. As a special form of grinding, the rotation of the tool in the z-direction is superimposed with an oscillating, high-frequency movement [ 8, 15 ]. The material removal basically corresponds to that of conventional grinding, but the grain cutting edges move in a sinusoidal path due to the oscillation, resulting in a fluctuating chip thickness [ 8 ]. This results in an improved tool lifespan and can lead to higher material removal rates for certain materials.
Laser processing of engineering materials is increasingly being used across a wide range of industrial sectors, offering advantages such as high precision, minimal heat-affected zones, and the ability to process complex geometries, making it a key technology in modern manufacturing [ 16 ]. Laser-assisted machining processes also offer a further possibility of achieving ductile material removal behavior and thus better machining conditions on hard-brittle materials [ 17 ]. The so-called l-LAM( laser-assisted machining) is a machining process that is used in the field of diamond turning and therefore works with a defined cutting edge. A laser beam is guided through the tool, a monocrystalline diamond, and focused into the interaction zone at the cutting edge. In the cutting zone, the hardness of the material to be machined is reduced by the thermal effect of the laser, whereby a locally limited ductile behavior of the hard-brittle material can be achieved. As a result, lower cutting forces and surface roughness as well as longer tool life can be achieved when machining hard-brittle materials [ 8, 18 ]. The advantages mentioned have already been illustrated in a number of publications. For example, Shahinian et al. were able to apply the l-LAM process using a Nd: YAG laser to optical precision components made of monocrystalline silicon. They found increased ductility, which led to a significant reduction in brittle fracture and increased the service life of the diamond tools used by up to 150 % [ 18 ]. Mohammadi et al. also found similar results in their investigations in which they presented a new laser-assisted diamond drilling process on single-crystal silicon. The Infrared Continuous Wave( IR-CW) fiber laser used reduced the hardness and brittleness of the material, resulting in ductile behavior, which also led to an increase in tool life. In addition, the quality of the leading edge and the surface finish on the lateral surfaces of the bore were significantly improved [ 19 ]. Kong et al. did investigations on silicon carbide ceramics and found a positive effect on axial and feed grinding forces which were 40 % lower as in conventional grinding [ 20 ]. Even for laser-assisted polishing processes investigated by Kim et al. a positive effect of the CO 2 laser on the material removal rate was observed [ 21 ]. Chen et al. also used laser-assisted single-point diamond turning( SPDT) to create microgrooves on singlecrystal silicon. They also found that laser support( IR fiber laser) improves the plastic deformability of hard-brittle materials and enhances their ductile properties. Furthermore, they confirm that the process is a promising, highperformance technology for processing hard-brittle materials in order to produce high quality surfaces and minimal damage in the component edge zone [ 22 ]. In some publications, there are also approaches to combine laser processes with grinding processes, i. e. with undefined cutting edges, and to investigate them on hard-brittle materials. For example, Chang et al. were able to realize a laserassisted grinding process that makes it possible to produce microstructures in high-strength materials such as silicon nitride and aluminum oxide. The use of a diode laser showed that laser-based grinding has a fundamentally similar grinding performance to a conventional grinding process. However, an improvement in the surface quality and less damage to the substrate was observed [ 23 ].
2 Motivation
In order to effectively optimize such laser-assisted processes described above and to develop new hybrid manufacturing processes based on them, a fundamental understanding of the thermal interactions between the laser radiation and the component surface is highly relevant. This approach is considered in the following for IR laser irradiation on fused silica glass samples. The findings are intended to be used to develop a new type of laser-assisted grinding process for optical and ceramic components, which should enable efficient and qualitatively optimized processing.
Based on the lLAM process, a fiber laser was selected for the investigations. The used fiber laser is characterized by a wavelength of 1070 nm which theoretically has a very low absorption on the SiO 2 material. For high laser absorption on glass components, the use of a CO 2 laser with a longer wavelength of 10.6 lm is generally recommended for applications such as laser polishing or cutting( see Fig. 1). However, in the approach by Yang et al., studies were conducted on mitigating damage growth, where it was demonstrated that heating with mid-infrared( 4.6 lm) lasers can be more efficient and better localized compared to far-infrared lasers [ 24 ].
If the laser impact on optical materials is too high, it can quickly lead to high thermal stresses and even damage to the component. In addition, the planned application should result in a laser-assisted grinding process as described above, whereby a water-based coolant must be used when grinding with diamond tools.
Although optical glasses exhibit a very low absorption rate in the infrared range at a wavelength of approximately 1 lm, this wavelength was still chosen for investigations into the localized heating of the glass surface. This decision is based on the following hypothesis: By increasing the surface micro-roughness Sq, the absorption rate increases. The absorption reaches its maximum value at the applied laser wavelength when Sq values approach approximately 1 lm. One reason for this is the increased occurrence of Fresnel absorption. If the micro-roughness is further increased, the absorption rate reaches saturation and subsequently decreases.
The hypothesis assumes that increased roughness alters the optical properties of the surface, enabling stronger interaction between the incident laser light and the glass surface. This could be attributed to scattering effects and changes in