In this study, we developed a machine-learning framework to predict the success of ultrafast laser microwelding of glass substrates based on plasma-emission spectra and laser-processing parameters. Ten-millimetre linear welds were produced under varying laser power, repetition rate, and scanning speed. The emission spectra collected during welding, combined with the corresponding processing conditions, were used to train support vector machine (SVM) and neural network (NN) classifiers. Both models demonstrated strong predictive performance, achieving over 80% accuracy on test data. Although a slight decrease in accuracy was observed on newly acquired data, this result highlights the potential for further improvement through data diversification. By expanding the dataset and incorporating environmental factors such as temperature and humidity, we aim to enhance the robustness and generalisation capability of the models. This approach offers a promising path toward improving the reliability and efficiency of ultrafast laser microwelding processes.
Fused silica is a cornerstone material in photonics thanks to its outstanding optical, thermal and mechanical robustness. Its surface can be selectively functionalized with CO2 lasers, whose strong infrared absorption confines energy to a thin layer and enables precise thermal effects-from annealing to ablation and laser polishing. Here we quantify how CO2 laser parameters govern crater morphology and the surrounding heat-affected zone (HAZ). Pits were machined with a 180 & micro;m-diameter focused beam using single pulses from 10 & micro;s to 2 s across the evaporative regime. Optical profilometry coupled with quantitative phase microscopy maps both topography and subsurface refractive-index changes, providing a rapid, non-destructive assessment of the HAZ. We show that, for a fixed removal depth, crater aspect ratio and HAZ width can be tuned independently by modulating pulse width and power: short, high-fluence pulses minimize collateral damage and favor smooth profiles. A two-dimensional finite-element model reproduces the transient temperature field and corroborates the experimental trends. The resulting guidelines enable high-precision CO2 laser processing of fused silica while mitigating HAZ and associated thermo-mechanical stress, microcracking and debris- crucial for generation of advanced optical components.
The feasibility of using beam shaped short femtosecond pulses in combination with a nonlinear frequency conversion process to create any arbitrary beam shape in the ultraviolet spectrum is shown. Broadband femtosecond pulses (800 nm centre, 30 nm Bandwidth FWHM, 50 fs) are shaped via a spatial light modulator (SLM) and converted to 400 nm in a subsequent second harmonic process to 400 nm in a collinear setup while conserving the beam shape information by using orthogonal polarisation states to avoid beam shape degradation. Additionally, it is shown, that the holograms exhibit blurred edges due to chromatic dispersion stemming from the bandwidth of the utilized fs pulses and the conversion efficiency is linked to the angular spectrum created at the SLM.
An alternative approach to conventional fabrication methods for optical components is the laser-based process chain. In that case, precise form generation can be achieved using ultrashort pulse (USP) laser ablation. Precise control of the ablation depth and surface roughness is a crucial requirement for optical applications. Current developments in USP laser beam sources lead to an increase in output power, enabling high harmonic generation with sufficient pulse energy for the ablation of glass materials. Optical glasses, depending on their specific chemical composition, show a drop in transparency in the UV-range. In this paper, the influence of the pulse duration, exemplary for 200 fs and 8 ps, on the ablation behavior of the optical glasses N-BK7 and P-SF69 is investigated comparing an IR-wavelength of 1030 nm to deep-UV-wavelengths of 257-266 nm. In contrast to IR-ablation, where the ps-pulse duration results in a more efficient ablation compared to fs-pulses, the ablation efficiency of N-BK7 is independent of the pulse duration in DUV. Furthermore, the surface roughness can be reduced to Sa < 0.14 & micro;m using DUV laser radiation. The ablation behavior of P-SF69 is melt-dominated, resulting in a smooth roughness down to Sa = 45 nm, near to optical quality.
The integration of low-cost collaborative robots (cobots) into laser materials processing (LMP) holds significant promise, especially for small and medium-sized enterprises (SMEs). Technological advancements have reduced costs and increased laser system flexibility, broadening their application. Additionally, demographic changes and labor shortages highlight the need for adaptable robotic solutions. Cobots, with intuitive programming, built-in safety, and low costs, suit SMEs performing small batch, varied production. However, their limited rigidity compared to industrial robots challenges precision and repeatability, demanding specialized path planning, calibration, and sensor fusion to ensure sub millimeter-level accuracy. This paper presents recent research on cobot-assisted LMP through laser cutting, welding, marking, and cleaning case studies. It discusses how optimized path planning, offline trajectory simulations, adaptive corrections, and hand-guided programming can overcome cobot limitations. The insights support broader adoption of cobots in laser materials processing and guide future research toward enhanced accuracy and effective human-robotcollaboration.
To evaluate the antibacterial performance of laser-induced periodic surface structures (LIPSS) formed on SUS430 stainless steel (equivalent to AISI 430, ferritic stainless steel), surface patterns were fabricated using femtosecond laser pulses (wavelength: 1030 nm; pulse duration: 150 fs) with controlled fluence. Two types of LIPSS were produced with average ridge and valley widths of approximately 410-nm and 380-nm/750-nm mixed structure, respectively. Antibacterial performance was assessed against Escherichia coli using the film-attachment method in accordance with the JIS Z 2801:2021 standard. Compared with the untreated SUS430 surface, the 410-nm LIPSS surface exhibited a reduction of approximately 83% in bacterial colony count, while the 380-nm/750-nm mixed structure showed a reduction of only about 31%. Fast Fourier transform analysis of scanning electron microscopy images revealed that the 410-nm structures had finer ridge and valley widths and higher structural uniformity. These findings suggest that the geometric characteristics of LIPSS, particularly ridge and valley width and uniformity, play a crucial role in enhancing antibacterial performance. This study demonstrates the potential of femtosecond laser processing as a novel approach to impart antibacterial functionality to material surfaces without the use of chemical agents.
This study addresses the challenges associated with scaling ablation rates while minimizing surface roughness for copper. By employing tailored flexible bursts, the temporal spacing and energy of individual pulses can be precisely manipulated, creating a high-dimensional parameter space for optimization. Traditional optimization methods are labor-intensive and time-consuming. Thus, we propose an automated Bayesian optimization approach that integrates advanced sensors and a microservice-based software platform for real-time adjustments. Our results demonstrate a multi-objective optimization of removal rates and surface quality, achieving efficiencies of up to 0.16 mm3/minW while reducing surface roughness to as low as 0.33 & micro;m. The findings indicate that effective process optimization by Bayesian optimization is plausible, with the potential for significant advancements in laser processing design. This work underscores the importance of combining Bayesian optimization with expert knowledge to enhance research efficiency and foster further investigations into optimal laser processing conditions.
Copper(II)-oxide-based femtosecond reductive laser sintering is applied to selectively produce high quality and flexible copper electrodes on ultra-thin glass with thicknesses between 30 and 100 & micro;m. To increase the precursor wettability and the later copper adhesion, the ultra-thin glass substrates are plasma activated. An amplified near infrared femtosecond laser combined with a galvanometric scanner is used to produce two-dimensional copper layers. Different laser and process parameters such as scan speed, laser power and repetition rate are varied to generate these structures with unrestricted design. The metallization rate can be significantly increased by adjusting the repetition rate in a new holistic parameter variation approach. This acceleration is accomplished by increasing the heat accumulation at higher repetition rates to reach the precursor temperature required for chemical reduction and sintering more rapidly. The copper structures are analyzed by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and 4-tip resistance measurement, respectively. In an optimized process regime, low electrical sheet resistances down to 117 m Omega/sq are achieved. A hybrid approach combining reductive laser sintering using infrared and laser drilling using ultraviolet femtosecond laser radiation is demonstrated, to produce a functional electrical circuit by employing the fundamental wavelength and the third harmonic of the same laser system.
Through-hole drilling of a 200-& micro;m-thick flame-retardant polyester-based film was investigated using a short-pulse CO2 laser with a pulse width of 304 ns. Percussion drilling was performed at a repetition rate of 200 Hz and a fluence of 10.7 J/cm2 per pulse. Two irradiation methods were examined. One was conventional continuous irradiation, referred to as Continuous Irradiation in this paper. The other was a method referred to as Divided Pulse Train Irradiation. In this method, a sequence of laser pulses (a pulse train) is followed by a certain time interval before the next pulse train is delivered. The minimum number of pulses required to form a through-hole was 75 in Continuous Irradiation, whereas only 4 pulses were sufficient in Divided Pulse Train Irradiation. In this case, 2 pulses were applied in the first set and 2 in the second set, with a time interval of 0.5 ms or longer. Discoloration was observed around the hole in Continuous Irradiation but was absent in Divided Pulse Train Irradiation, suggesting that thermal effects were effectively suppressed in the latter.
We report for the first time on the flexible and large-area 2D laser cutting of ultra-thin glass using an ultrashort pulsed laser robot (USPLR) system emitting at a wavelength of 1030 nm. To optimize the cutting quality of 100 & micro;m thick AF 32 eco ultra-thin glass substrate, experiments were performed with different laser pulse durations, laser pulse energies, laser pulse repetition rates and robot speeds. For the evaluation of the cutting quality, crack formation and induced stresses near the cutting edge were analyzed using imaging polarimetry and digital microscopy. At robot speeds of up to 40 mm/s, crack formation occurs at laser pulse durations greater than 1 ps. Using a laser pulse duration of 1 ps, laser pulse energies of up to 140 & micro;J and a laser pulse repetition rate of 200 kHz, complete cuts are produced in a wide processing window at robot speeds of 15 mm/s to 65 mm/s without crack formation. In addition, when using a laser pulse repetition rate of 400 kHz and a laser pulse energy of 80 & micro;J, the processing window is extremely enlarged due to heat accumulation effects. However, at the high robot speeds of up to 80 mm/s, unevenness and notching of the cutting edges are observed as a result of vibrations of the USPLR system during laser cutting, limiting the potential processing speed. An ultrathin glass component is produced with sharp and rounded cutting edges, demonstrating the high potential of the USPLR system for the flexible and large area 2D laser cutting applications in various industrial sectors.
Processing heat-sensitive materials like glass requires minimizing thermal damage, a challenge for conventional nanosecond lasers. While ultrashort pulsed lasers offer precision, their efficiency can be limited. This study presents method to enhance glass processing by using a mixed-pulse-train (MPT) of synchronized picosecond (ps) and nanosecond (ns) pulses. We demonstrate that this simultaneous approach significantly improves ablation efficiency on soda-lime glass by determining the influence of the nanosecond pulse on the ablation threshold. The ablation threshold was reduced from 3.38 J/cm2 with ps-only pulses to 2.79 J/cm2 in MPT mode. This enhancement is critically dependent on the temporal delay, with the lowest threshold achieved when the ns pulse trails the ps pulse by 5 ns. This indicates a synergistic effect where the ps pulse pre-excites the material, increasing the absorption of the following ns pulse. Furthermore, MPT processing resulted in distinct topographical changes, including a wider modification zone and surface elevations up to 40 nm, suggesting localized volume expansion. These findings show that synchronized ps-ns pulses provide a highly controllable method for tailoring material interactions, offering a promising alternative to more complex and costly burst-mode systems for high-precision applications.
We report on an automatic laser beam focus monitoring approach for an ultrashort pulsed laser robot system. The system integrates an ultrashort laser mounted on a link of a six-axis industrial articulated robot with a galvanometer scanner and an F-Theta lens mounted on the end of the last robot axis. This enables high precision micromachining using ultrashort pulsed laser over a large 3D processing area. A beam focus monitoring and adjustment method combining a distance sensor and cameras ensures consistent processing quality during extensive robot movement. A conventional beam focus monitoring algorithm based on image processing is compared with a deep learning-based method using YOLO object detection network, where a high accuracy is particularly observed using YOLO network-based method. In addition, the methods are implemented in the system and utilized for the beam focus monitoring for an ablation process of fused silica, with varying the processing surface orientations. Both methods demonstrate the capability for a correct beam focus detecting with surface orientations ranging from -30 degrees to 15 degrees, while maintaining the beam propagating axis parallel to the surface normal.
An in-line monitoring system for ultra-short pulsed (USP) laser ablation was developed and assessed to two-dimensionally map the complete removal of a thin film. This method enables single pulse resolved monitoring based on Laser Induced Breakdown Spectroscopy (LIBS) for pulse repetition rates of up to 4 MHz. The transition from one 1.5 & micro;m thin layer to another during laser ablation was detected. The mapping with Energy-dispersive X-ray Spectroscopy and our method are in very good agreement. Furthermore, an enhancement of the signal contrast was achieved with GHz bursts.
For the contacting of battery cells, a stable and time-efficient joining process is required, whereas primarily copper and aluminum materials with high electrical conductivity are used. To ensure a high level of automation and process efficiency, laser micro welding has established itself in industrial applications. Single-mode fiber lasers in the near-infrared range with high brilliance offer the possibility of achieving high welding depths, although more than 90% of the initial laser power is lost due to reflection losses irradiating copper materials [1]. Laser beam sources in the blue emission spectrum, by contrast, have higher absorption in copper or aluminum, but cannot yet be focused to comparably small spot diameters in the required power range. To combine the advantages of both approaches, this paper follows the principle of spatial beam superposition of 445 nm and 1070 nm lasers, pursuing the goal of influencing precision-determining weld seam properties of copper and aluminum. This includes the formation of the melt pool, the consistency of the process regarding the welding depth and the influence on the surface roughness. As materials, Cu-ETP, CuSn6 and EN AW-6082 are analyzed to investigate the influence of different thermal conductivities on the process in addition to different base materials.
This study demonstrates a dual-functional microwire fabricated from Indium Tin Oxide (ITO) film. A nanosecond ultraviolet (UV) laser scriber system is used for the ITO surface scribing. We fabricated two transparent microwire and demonstrated that the single wires achieved both heating and sensing functionalities. For heating purpose, the microwires were applied with a bias voltage for achieving Joule heating effect. The electrical current through the microwire was simultaneously measured for obtaining the resistance of the microwire by Ohm's law. The temperature was thus obtained by the temperature coefficient resistance (TCR) curve of the microwire. We also tested the effect of oxygen plasma treatment on the ITO microwires' TCR. It was found that the TCR slope increased by nearly 20%, indicating enhanced temperature sensitivity. In addition, we analyzed surface morphology and heat-affected zones (HAZ) of the laser-ablated region. The surface characterization showed that longer pulse duration and increased energy density resulted in a significant increase in rim height but not notable surface roughness changes. This dual-functional ITO micrometer heater/sensor enabled a temperature gradient of similar to 5 degrees C/mu m at 100 degrees C, which demonstrated its excellent potential for precise thermal control and sensing applications.
An infrared femtosecond laser pulse was focused on an anthracene crystal surface to generate a stress wave, and its propagation on the crystal was detected by an atomic force microscope (AFM). Additionally, femtosecond laser pulses were employed to modify the crystal surface. The wave propagation velocity was estimated from the delay time between the pulse irradiation time and the first response of cantilever, which depended on the distance between the laser focal point and the contact point of cantilever. Utilizing partial least squares discriminant analysis (PLS-da) of the waveform of the cantilever response, we found that propagation behavior of the wave was modified between unmodified and laser-modified surfaces. These results suggested that the detected wave propagation was dominated by the surface acoustic wave (Rayleigh wave). The propagation velocity of the surface waves provides the Young's modulus of the crystal, which was estimated to be 655 MPa. This is much smaller than that (5 GPa) estimated by the conventional AFM indentation test. These respective values are considered to predominantly reflect the in-plane and out-of-plane mechanical properties of the anthracene crystal surface. We show a novel method for characterizing in-plane mechanical properties of organic crystal surfaces.
Indium Tin Oxide (ITO) is widely used material for example in displays or solar cells. In this work we focused on increasing the productivity and processing quality of ultra-short pulsed laser ablation of ITO with MHz and GHz bursts. Thick ITO films could not be ablated with one pulse, preventing optical stamping. With MHz bursts thick (200 nm) ITO films could be completely removed with one burst. Moreover, the ridge height around the ablated lines were diminished. On the other hand, GHz bursts could not completely remove the ITO film. Ablation with bursts with tens of sub-pulses result in ablation results in increasing ridge height. With MHz bursts the productivity and quality could be enhanced.
Our earlier study revealed that the efficiency of laser drilling using long pulses (LPs) of a conventional Nd:YAG laser was significantly higher than that using nanosecond pulses (NSPs). To elucidate a factor attributable to the higher efficiency of LPs, plasma shielding in laser ablation of Ni foils using LPs and NSPs was investigated using pump-probe techniques. Results showed that probe laser attenuation caused by laser ablation using LPs was lower than that using NSPs. This result strongly suggests that the lower degree of plasma shielding contributes to the higher drilling efficiency of LPs. Additionally, it was suggested that plasma shielding in LP ablation is mainly due to metal vapor, whereas that in NSP ablation is caused by atoms and ions.
Beam shaping is a crucial aspect in the field of laser materials processing. Among the optical elements available for this purpose, Diffractive Optical Elements (DOEs) stand out due to their robustness and versatility. However, a flexible fabrication method is desirable to facilitate rapid testing of different beam shapes using various DOEs. Two-Photon Polymerization (2PP) is a promising fabrication technology for this purpose, as it allows the creation of arbitrarily shaped three-dimensional structures with a resolution down to 100 nm and excellent surface quality. In this work, a DOE was fabricated using 2PP, which modulates the light into a set of two ring beams. The phase input was calculated as a computer-generated hologram using the prism and lens algorithm, where the term for the axial focus shift was substituted by an axicon hologram. The DOE has a diameter of 3.5 mm and a maximum height of 6.4 mu m. To fabricate this DOE, the phase input image was converted into a corresponding three-dimensional STL file depending on the gray level of each hologram pixel. After fabrication, beam shaping properties of the DOE were analyzed using a beam profiler to visualize the resulting two ring beams. Damage threshold experiments validated the robustness of the DOE for material processing.
We present a high-resolution spectroscopic characterization of the frequency-doubled output (532 nm) of an industrial-grade picosecond Nd:YAG laser. A Michelson interferometer with a PIDcontrolled linear stage was used to provide the path delay change during taking the interferogram, despite its non-uniform motion which in general prohibits direct Fourier-based spectral reconstruction. We introduce a correction scheme combining inverse FFT artefact suppression and a matched-filter approach to recover the true spectral content with sub-nanometer accuracy. The most probable emission peak was determined at 531.844 nm with a FWHM of 0.0437 nm, in good agreement with literature values for Nd:YAG fluorescence peaks. Our method enables precise spectral measurements, without resorting to phase-stabilized scanning methods or calibrated spectrometers.
