The ablation of solid materials using ultrashort laser pulses at high intensities leads to the emission of X-rays. This effect is particularly pronounced when burst pulses are applied due to pulse-to-pulse interactions within a burst. Simultaneously, the resulting surface topography changes depending on whether single pulses or burst pulses are used. This study experimentally investigates the spectral X-ray emission during the ablation of 304L-steel with single and burst pulses, varying the detection angle and predefined laser parameters. The aim is to analyze how surface topography, which evolves during ablation, influences the measurements of X-ray emission during area irradiation. The results indicate that surface topography-induced shielding of X-ray emission occurs for single and MHz-burst pulses, but only at fluences where characteristic surface structures form. In the MHz-burst regime, additional shielding effects arise from interactions with the ablation plume, which also contribute to a shift toward higher-energy X-ray photons. In contrast, GHz-burst pulses preserve a smooth surface across all investigated fluences, preventing shielding of X-rays.

Ultrashort laser excitation of dielectric materials is governed by a complex interplay between nonlinear photoexcitation, transient optical response, and energy transfer to the lattice. A consistent physical description of these processes across different pulse durations remains challenging, as purely free-electron-based optical models and classical thermal approaches do not adequately capture the strongly dynamic and non-equilibrium nature of the excited electron system. In this work, a coupled modeling framework is developed for amorphous fused silica (SiO2) that directly links the transient optical response to a density-dependent two-temperature description of the subsequent thermal evolution. The optical properties are described using a hybrid Lorentz-Drude formalism, enabling a consistent representation of bound, localized, and free electronic states during excitation. The resulting energy deposition is coupled to a modified thermal model incorporating electron-density-dependent material parameters derived from first-principles calculations. The model is evaluated by comparison with experimentally measured ablation geometries and single-pulse ablation thresholds for pulse durations in the femtosecond and picosecond range. The threshold analysis indicates that experimentally measurable material removal can occur below the model-internal phase-explosion criterion, particularly for longer pulse durations. In the femtosecond regime, both ablation depth and diameter are reproduced within a limited deviation range. In the picosecond regime, the ablation depth remains consistent with experimental observations, while systematic deviations in the lateral extent become apparent. At longer pulse durations, the experimentally observed structures are increasingly influenced by melt-mediated material redistribution, which is not captured by the present model and leads to pronounced deviations in the ablation geometry. These results demonstrate that the proposed framework provides an effective physical description of ultrafast laser-matter interaction in non-equilibrium and transition regimes, while also defining its limitations in thermally dominated regimes where hydrodynamic effects become significant.

Results on the ablation of stainless steel using ultra-short single, double and quadruple pulses as a function of the fluence and the time delay between each laser pulse are presented. The investigations focused quantitatively on the ablated volume and the resulting ablation efficiency, and qualitatively on the topography of the structures produced, providing insights about physical mechanisms such as shielding, re-deposition of ablated particles, and accumulation of heat or energy. The results indicate a significant influence of fluence in combination with the time delay on the ablation process and the resulting ablation topography.

The authors present results of ablation on silicon with ultrafast laser radiation featuring burst pulses using an amplified burst-mode solid-state laser, featuring an emitting wavelength of 1030 nm to generate single burst cavities on silicon. Laser parameter are varied for different pulse durations from 270 fs up to 10 ps, burst fluences, and number of sub-pulses per burst in the respective burst regime with sub-pulse repetition rates of 65 MHz and 5 GHz. The resulting ablated volume per burst and per sub-pulse in a burst as well as the topography are investigated and discussed.

The authors report on the use of a burst-mode ultrashort pulsed laser source with an emitting wavelength of 1030 nm on to micro-machining plane areas of glass with different pulse durations, burst energies, and number of sub-pulses per burst with intra-burst rates of 65 MHz and 2.5 GHz. In the investigated parameter range, the maximum specific removal rates are obtained with $$11.2\,\upmu \text{m}^{3}/\upmu \text{J}$$ for MHz bursts and $$27.0\,\upmu \text{m}^{3}/\upmu \text{J}$$ for GHz bursts, being up to four times higher compared to the non-burst regime. The depth per scan and the surface roughness increase at higher burst energies and at a higher number of sub-pulses per burst, respectively. Furthermore, a significant difference in the resulting surface topography between MHz and GHz bursts is shown by SEM images, mainly depending on the number of sub-pulses per burst.

In this study, an ultrashort pulse laser is used to investigate the removal efficiency and the ablation quality of stainless steel. The employed solid state laser is capable of varying the pulse duration from 0.27 to 10 ps and generates bursts with an intraburst pulse repetition frequency of 65 MHz with up to nine pulses per burst. Depending on the fluence per pulse, the pulse duration, and the number of pulses per burst, the removal efficiency and the ablation quality are presented and discussed based on the depth of the ablation structures and the surface roughness of the structured bottoms. The results prove that compared to pulse durations in the picosecond regime, the ablation efficiency in the femtosecond regime is significantly higher. The removal efficiency per burst is not affected by an increase in the number of pulses in the burst, but a smoothing effect can be identified for a certain number of pulses in the burst depending on the fluence and the pulse duration, which has a positive effect on the ablation quality. The temperature distribution and the heat accumulation induced by the high intraburst pulse repetition frequency are calculated with a semiempirical two-temperature model. The simulation results demonstrate that the melting film depth has a major influence on the smoothing effect caused by the burst mode.

In this study, the generation of 3D microstructures in stainless steel with ultrashort laser pulses using different burst modes will be presented. Femtosecond laser pulses in the BiBurst mode and picosecond laser pulses in the MHz burst mode are used to generate a predefined 3D microstructure. To smooth the structure bottoms and to remove deposits, a novel subsequent processing technique using femtosecond laser pulses in the GHz burst mode is performed. Two different processing strategies of the ablation and the subsequent treatment are applied to generate predefined 3D microstructures with low surface roughness and without deposits. In this way, smooth structure bottoms with a minimum surface roughness of 0.13μm can be obtained at a structure depth of 300μm.

Ultrashort pulsed laser sources generating pulse trains (bursts) with intra-burst repetition rates in the MHz and the GHz regime enable an efficient production of microstructures with a high surface quality. However, x-ray radiation can be generated during the laser micromachining using large intensities of the laser radiation and its interaction with the ablation cloud or high-density plasma. Therefore, the authors report on the interaction of bursts with a wavelength of 1030 nm and pulse durations of 0.24 and 10 ps with intra-burst repetition rates of 65 MHz (MHz-burst mode) and 2.5 GHz (GHz-burst mode) as well as a combination of both burst modes, called BiBurst mode, with stainless steel, and the x-rays are generated. The x-ray dose rates determined in the respective burst modes are compared and discussed with those of conventional ultrafast laser radiation (single-pulse mode). Furthermore, a theoretical model is used to calculate the expected x-ray dose rates. In the investigated parameter range, the highest dose rates of more than 105μSv/h are determined at a specific burst setting. Compared to the single-pulse mode, significantly higher dose rates are determined using the burst mode with the same total intensity. Based on the results of this study, it can be stated that the interaction of ultrafast laser radiation in the burst mode with a generated ablation cloud or high-density plasma plays a major role in x-ray generation and the resulting x-ray dose rates.

The authors report on the results of surface treatment experiments using a solid-state amplified laser source emitting laser pulses with a pulse duration of 10 ps. The laser source allows the generation of pulse trains (bursts) with an intra-burst pulse repetition rate of 80 MHz (pulse-to-pulse time interval about 12.5 ns) with up to eight pulses per burst. In this study a wavelength of 1064 nm was used to investigate both ablation of material and laser-induced surface modifications occuring in metallic implant alloys CoCrMo (cobalt-chromium-molybdenum) and TiAlV (titanium-aluminum-vanadium) in dependence of the number of pulses and fluences per pulse in the burst. By using the burst mode, a smoothing effect occurs in a certain parameter range, resulting in very low surface roughness of the generated microstructures. It is demonstrated that at fluences per pulse which are smaller than the material-specific ablation threshold, a self-organized pore formation takes place if a defined number of pulses per burst is used. Thus, the advantage of the MHz burst mode in terms of a possible surface modification is established.

This study intends to present a simple two-temperature model (TTM) for the fast calculation of the ablation depth as well as the corresponding effective penetration depth for stainless steel by considering temperature-dependent material parameters. The model is validated by a comparison of the calculated to the experimentally determined ablation depth and the corresponding effective penetration depth in dependence on the pulse duration (200 fs up to 10 ps) and the fluence. The TTM enables to consider the interaction of pulsed laser radiation with the electron system and the subsequent interaction of the electrons with the phonon system. The theoretical results fit very well to the experimental results and enable the understanding of the dependence of the ablation depth and of the effective penetration depth on the pulse duration. Laser radiation with a pulse duration in the femtosecond regime results in larger ablation depths compared to longer-pulsed laser radiation in the picosecond regime. Analogously to the ablation depth, larger effective penetration depths are observed due to considerably higher electron temperatures for laser radiation with pulse durations in the femtosecond regime.

The authors report on a solid state GHz amplified laser source capable of varying the pulse duration in the range of 270 fs to 10 ps and generating a pulse train with an intra-burst pulse repetition rate of 5 GHz (pulse-to-pulse time interval approx. 200 ps). In this study, a laser radiating at 1030 nm wavelength is used to investigate the ablation and surface quality on stainless steel, cemented tungsten carbide and silicon with different pulse numbers per burst between one pulse and 25 pulses. As a consequence of shielding effects by the laser-induced plasma or by the ablation cloud, no material tends to be ablated in burst mode for all tested pulse durations at this intra-burst pulse repetition rate. Compared to the non-burst regime, a reduction of the surface roughness by a factor of four could be accomplished depending on the number of pulses per burst. Thus, the actual advantage of the GHz burst regime in terms of the obtainable surface quality could be established.

An ultrashort pulse laser, capable of varying the pulse duration from 0.2 ps up to 10 ps, is used to study the ablation characteristics of stainless steel and cemented tungsten carbide. In addition to the influence of pulse duration, the number of pulses and the wavelength are examined for their influence on the ablation process. By determining the ablation diameter of generated cavities, the ablation threshold of the materials is calculated as a function of the number of pulses, the pulse duration, and the wavelength. The experimentally determined ablation thresholds tend to agree with calculated values. Due to the incubation effect, the ablation threshold decreases with increasing the number of pulses. In this context, the incubation factor (0.81@1030 nm and 0.80@515 nm for stainless steel, 0.90@1030 nm and 0.77@515 nm for cemented tungsten carbide) for the investigated materials is determined. On the basis of the measured ablated volume, the effective penetration depth (a reduction in a range from about 12 nm and 15 nm to 6 nm for stainless steel and in a range from 22 nm and 32 nm to 11 nm and 13 nm for cemented tungsten carbide by increasing the pulse duration from 0.2 ps to 10 ps) of the energy is calculated and it is proven that in the femtosecond regime the penetration depth increases compared with the picosecond regime. In consequence, the efficiency of the ablation process is increased by using shorter laser pulses.

This study presents experimental and theoretical results of material removal of cobalt chrome alloy (CoCrMo) using high-frequency picosecond laser pulses. Depending on the fluence and number of pulses in a burst, structures are created to be able to determine the ablated volume per pulse in burst, the structure depth and the surface roughness. A single pulse in the burst represents the ordinary pulsed laser radiation. Depending on the number of pulses, the ablated volume per pulse and the achieved depth of the structure, respectively, rises in the burst. Furthermore, a smoothing effect on the machined surface is revealed depending on selected parameters. An energy-dispersive X-ray analysis demonstrates that the stoichiometry remains the same after material processing in burst mode. To be able to simulate the material removal as well as the accumulated residual heat, the required parameters such as threshold fluence, effective penetration depth and the incubation factor are determined experimentally. The simulations demonstrate that laser-induced heat accumulation contributes to material removal and establish the smoothing effect through the use of the burst mode.

This paper presents results obtained by studying material removal of silicon and cemented tungsten carbide using high-frequency ultrashort-pulsed laser radiation. In laser-induced material removal, ablation mechanisms and heat accumulation effects are considered. Depending on the fluence and number of pulses in a burst, structures are created on silicon and cemented tungsten carbide in order to be able to determine the ablated volume. A single pulse in the burst represents the conventionally pulsed laser radiation. Depending on the number of pulses, the ablated volume per pulse rises in the burst. Furthermore, an increase in the number of pulses in the burst results in a repetitive decrease as well as an increase in the ablated volume. Investigations at different ambient pressures establish that this phenomenon could be changed for cemented tungsten carbide under fine vacuum. The simulations demonstrate that the laser-induced heat accumulation in burst mode contributes significantly to the removed volume.

This paper presents results obtained in high-pulse repetition frequency ultrashort pulse laser microprocessing of copper. In the study, a variety of ultrashort pulse laser systems supplying high average laser power were applied in order to investigate the influence of the laser parameters on copper ablation. For this, laser pulses of different wavelengths (515 nm, 1030 nm) and pulse durations, ranging between 200 fs and 10 ps, were irradiated to the sample surface by raster scanning of the laser beam. The dependencies of average laser power, pulse energy, and the pulse repetition rate on the ablation rate, the ablation efficiency, and the productivity were studied. A maximum average laser power of 31.7 W was applied in this work. The pulse repetition rate was varied in the rage between 0.2 and 19.3 MHz. Finally, the machining qualities obtained were evaluated by means of surface roughness measurements and scanning electron microscope micrograph analysis.

This paper presents results obtained in high-PRF (pulse repetition frequency) ultrashort pulse laser micro processing of copper. In the study, a variety of ultrashort pulse laser systems supplying high average laser power were applied in order to investigate the influence of the laser parameters on copper ablation. For this, laser pulses of different wavelengths (VIS, NIR) and pulse durations, ranging between 200 fs and 10 ps, were irradiated to the sample surface by raster scanning of the laser beam. The dependencies of average laser power, pulse energy, and the pulse repetition rate on the ablation rate, the ablation efficiency, and the productivity were studied. A maximum average laser power of 31.7 W was applied in this work. The pulse repetition rate was varied in the rage between 0.2 MHz and 19.3 MHz. Finally, the machining qualities obtained were evaluated by means of surface roughness measurements and SEM micrograph analysis.