We will present recent developments in femtosecond lasers based on Holmium materials emitting around 2.1µm, including modelocked disk lasers with record high average power based on Ho:YAG and new GHz high-power oscillators with sub-100 femtosecond pulses using the new material Ho:CALGO. We will also discuss areas of application where these lasers promise to open new opportunities.

We present in this contribution a Yb:YAG thin-disk multipass amplifier delivering sub-2 ps pulses with kilowatt of average output power at a highly flexible repetition rates ranging from MHz to several GHz. The system, developed within the european project kW-Flexiburst, delivers laser pulses from single pulse to bursts of pulses with arbitrary number of pulses (1, 3, 5, …, 1000) at up to 7.5 GHz of intra-burst repetition rate. A seed laser delivering stretched pulses at an average output power of 50 W for a single pulse configuration and up to 230 W for GHz-bursts with more than 3 pulses/burst was used. In a single pulse configuration, an average output power of up to 655 W whereas up to 1090 W were extracted in burst operation at an intra-burst repetition-rate of 1GHz. During the talk, few examples of applications using our laser will be presented.

In this experimental study, a high power femtosecond laser delivering long GHz bursts was use to compare the influence of the wavelength on the quality and the specific ablation rate of selected materials.

Here, we present very low pulse energies (below 200 nJ) at very high speed (over 100 kHz) LIBS experiment by employing our recently developed 25 ps, 14W, 2.8 GHz intra-burst repetition rate Yb-doped fiber laser system. To carry out the LIBS experiments, the laser beam is directed into a Galvo scanner and focused through a 56 mm long F-theta lens onto different materials, including steel, copper, aluminum, and silicon. Our investigation of LIBS encompassed various parameters, including varying pulse energies, the number of intra-burst pulses, and burst repetition rates. For instance, with a burst repetition rate of 100 kHz with 83 ns burst width (232 intra-burst pulses), we observed the threshold pulse energy stands at approximately 26 nJ for LIBS experiment on steel. Furthermore, at about 200 nJ, it is enough to keep a high signal-to-noise ratio. To the best of our knowledge, this is the first report on LIBS experiment by GHz-range laser operating in the burst mode regime.

In this presentation, we introduce a novel approach to machining surfaces using femtosecond (fs) UV laser systems. We explore the potential of these systems for large-area surface patterning, specifically in processing high band-gap materials like sapphire and yttrium aluminium garnet (YAG). The existing techniques are not satisfactory in terms of etch rates and accuracy, which our research is addressing. We demonstrate the use of two-beam fs-UV interference patterning to create harmonic gratings with exceptional accuracy. Key aspects include controlling the pulsed nature of the beams, optimizing pulse delay and spatial overlap, and comparing various beam splitting techniques. Our findings indicate that we can achieve sub-25 nm precision in material removal, which is a significant improvement over existing technologies. This research not only enhances the efficiency and accuracy of surface machining but also opens up new possibilities in advanced photonic applications.

Laser Shock Peening has shown in the past decades its efficiency over other techniques to enhance the fatigue resistance of parts. However, its use is still limited to certain applications as it is complex to implement (high-footprint, free-space propagation, sacrificial layer management). In this publication, we introduce the Fibered Laser Shock Peening System (FLASP), which consists of a fiber coupling module, an optical head to focus the beam on the part, and an optical fiber to link both modules. Energetic laser beam transmission through optical fibers requires specific beam shaping as it is necessary to suppress spatial profile modulations caused by speckle. For this matter, the spatial coherence of the beam was reduced in order to obtain a smooth circular beam profile at the fiber entrance. Such a setup made it possible to couple a record 380mJ in a 1.5mm core optical fiber which corresponds to a peak power of 63MW at a pulse duration of 6ns. Such energy levels have not damaged a 5m fiber for more than 50 million shots. The FLASP system successfully treated aluminum, titanium and steel parts for which compression peaks reached -400MPa while the affected depth exceeded 1mm.

We will present recent advances in direct bonding of dissimilar materials like glass to metal, silicon or ceramics using ultrashort lasers. The process can potentially displace traditional bonding techniques such as epoxy, diffusion, anodic, etc offering a clean, fast and flexible new alternative. It relies on highly controlled laser heat input from <10ps pulses along a user-defined toolpath at the material interface and has been proven to work on various material combinations including BK7, quartz, fused silica, sapphire glasses of varying size, thickness and shape with metals (aluminium, s.steel, titanium, etc), silicon and ceramics (silicon nitride).

We applied the 3D fabrication capability of ultrafast laser to fabricate 3D functional micro and nanodevices for chemical and biological applications. Applications of the fabricated devices include 3D micro and nanofluidic systems to elucidate mechanism of cancer cell metastasis and invasion in the human body, diagnostic microchips based on advanced digital nucleic acid amplification technique (d-NAAT), such as digital polymerase chain reaction (d-PCR), which consists of an array of more than 10,000 micro-through-holes on glass substrates, and 3D microfluidic surface enhanced Raman spectroscopy (SERS) chips enabling real-time sensing and attomolar level sensing of chemical and biological samples.

The exploration of sustainable materials derived from natural sources gains prominence, attributing to their renewable nature and minimal ecological footprint upon disposal. Integrating such sustainable materials into the design of electrical and optical devices holds the promise of realizing an ecologically harmonious society. In this presentation, our study on laser-induced carbonization and graphitization of natural materials using a femtosecond laser will be described. Specifically, we demonstrate the direct patterning of conductive structures on biodegradable materials by laser-based graphitization. By measuring the temperature of the material by varying the repetition rate of laser pulses, we revealed that the properties of the generated material change not only based on the highest temperature but also on the temporal variation of temperature. Furthermore, we have expanded the technique for the fabrication of a metal-free supercapacitor and triboelectric nanogenerator (TENG) by laser-induced graphitization.

The electric double-layer capacitor (EDLC) is an energy storage device distinguished by its relatively extended cycle life and rapid charge-discharge capabilities. Heightened capacitance of the EDLC aligns with an augmented specific surface area of the electrodes. In this study, we employed laser-induced graphitization of a biodegradable composite sheet containing NaHCO3 to fabricate a conductive porous carbon structures serving as EDLC electrodes. Pores were observed on the surface of the composite sheet containing NaHCO3 after laser irradiation. It is considered that the formation of pores, accompanied by gas generation from the thermal decomposition of NaHCO3, led to an increase in the specific surface area of the structures and improved capacitance. Our method extends the potential of environmentally compatible, plant-derived materials for device applications.

Among different technologies dealing with additive manufacturing (AM), Laser Induced Forward Transfer (LIFT) is a sustainable and precise manufacturing technology, that shows high potential for industrial application. Here, we propose the use of LIFT to efficiently print metallic patterns and solder materials on PIC chips. This study explores two donor substrates for gold deposition: evaporated gold layers on glass and gold nanoparticle inks, and one donor substrate for solder paste deposition. Parameters like layer thickness, laser scanning speed, donor-receiver gap distance, laser fluence and pulse shape are optimized for quality transfer. Optimization of the LIFT process parameters will enable the reproducible and controllable printing of electrodes for creating an all-printed graphene-based photodetector and the solder paste deposition for assembly applications.

Multiphoton Lithography stands as a laser-driven additive manufacturing method, enabling the creation of structures with remarkable resolution, reaching down to the scale of tens of nanometers. Leveraging nonlinear absorption, this technique boasts distinctive capabilities unmatched by other methods. Diverse materials have been successfully employed in its implementation, resulting in the production of various components and devices such as metamaterials, biomedical devices, photocatalytic systems, and mechanical models. The distinguishing feature of Multiphoton Lithography lies in its ability to actualize computer-designed, fully operational 3D devices. This presentation provides a comprehensive overview of microfabrication principles, highlighting recent advancements in materials processing and the functionalization of 3D structures. To conclude, an exploration of future applications and the technology's prospects is presented.

This study addresses the challenges of adding functionality and hybridizing processes in additive manufacturing. It focuses on embedding a gold-coated optical fiber into an INOX structure, aiming to extend this process to optical sensors like fiber Bragg grating arrays. The primary concern is the sensor's resistance to high temperatures during metal deposition, while the second challenge involves the adhesion of filler material to the sensor and structure. The feasibility is assessed through a finite element thermal model and mechanical testing, confirming the process's viability. Successful light transmission through the fiber and tensile tests indicate structural integrity and reduced ductility, warranting further investigation under varying load conditions.

Unraveling the emergence of spontaneous patterns on laser-irradiated materials has been a long-standing pursuit. Periodic surface structures manifest as a result of multiphysical coupling involving electromagnetics, nonlinear optics, plasmonics, fluid dynamics, and thermochemical reactions. Periodic surface structures result from multiphysical coupling: electromagnetics, nonlinear optics, plasmonics, fluid dynamics, and thermochemical reactions. Multi-shot ultrafast laser pulses generate stable periodic patterns influenced by disturbances and nonlinear saturation. Describing pattern growth requires a model with symmetry breaking, scale invariance, stochasticity, and nonlinear properties. Stochastic Swift-Hohenberg modeling replicates hydrodynamic fluctuations near the convective instability threshold in laser-induced self-organized nanopatterns. We demonstrate that deep convolutional networks can learn pattern complexity, connecting model coefficients to experimental parameters for specific pattern design. The model predicts patterns accurately, even with limited data, identifying laser parameter regions and predicting novel patterns independently.

We exploited known effects of surface plasmon polariton (SPP) coupling into structured surfaces to suppress Laser-induced Periodic Surface Structures (LIPSS) growing around a hole-shaped seed structure. Holes ranging from 200 nm to 1500 nm in diameter were first created in the surface of a fused silica sample and then irradiated with a single femtosecond laser pulse (800 nm, 30 fs). For small diameters, Type-I LIPSS, typically related to metallic materials, appeared around the seed structure. For seed diameters around the laser wavelength, where the SPP coupling is hindered, the LSFL-I vanished. For larger diameters, they reappeared accompanied by additional LSFL-II, which have perpendicular orientation and are typical for dielectrics. Selectively deactivating SPP contribution to LIPSS generation can help elucidate the underlying processes, which are still a matter of debate.

Laser-induced crystallization is a novel alternative to classical methods for crystallizing organic molecules but requires judicious choice of experimental parameters for the onset of crystallization to be predictable. This study investigated the impact of the laser repetition rate on the time delay from the start of the pulsed laser illumination to initiation of crystallization, the so-called induction time. A supersaturated urea solution was irradiated with near infrared laser pulses with an intensity of 1E14 W/cm2 while varying the repetition rate from 10 to 20 000 Hz. The optimal rate discovered ranged from 500 Hz to 1 kHz, quantified by the measured induction time (median 2-5 seconds) and the mean probability of inducing a successful crystallization event (5E−2 %). For higher repetition rates (5 kHz to 20 kHz), the mean probability dropped to 3E−3 %. The reduced efficiency at high repetition rates is likely due to an interaction between an existing thermocavitation bubble and subsequent pulses. These results suggest that an optimized pulse repetition rate can be a means to gain further control over the laser-induced crystallization process.

Femtosecond laser inscription is a unique approach to achieve non-conventional manufacturing of integrated photonic devices such as laser waveguides. Our approach relies on sensitized glasses containing both silver and Ytterbium ions. Laser inscription allows for the 3D-localized production of highly luminescent molecular silver clusters that support waveguiding architectures. We demonstrate efficient energy transfers from silver clusters to Ytterbium, allowing for background-free 3D-localized near-IR emission. Near-IR laser amplification under indirect pumping is demonstrated, depicting the localized creation of a hybrid laser gain medium involving silver clusters and Ytterbium ions as donor/acceptor pairs. Further work targets to demonstrate integrated laser behavior.

Understanding laser-induced plasma formation dynamics is pivotal for controlling the energy density deposited within the solid dielectrics during ultrafast laser material processing. Conventional numerical codes, however, fail to reproduce the propagation dynamics of tightly focused Bessel beams, which are widely used for stealth dicing. We adapted the massively parallel Particle-In-Cell (PIC) code EPOCH, incorporating background permittivity and Keldysh field- and impact-ionization modules. We compare numerical simulations to experimental results across various imaging diagnostics. Our simulations enabled the identification of the pivotal processes governing dense plasma formation and reproduced the high energy density experimentally observed.

Ultrashort pulse (USP) laser processing has great potential for precise microfabrication. Toward higher quality and productivity, we have developed the data-driven USP laser processing in which process parameters can be controlled based on data such as in-process monitoring and artificial intelligence (AI) optimization. In this work, stable formation of laser-induced periodic surface structure (LIPSS) in nanoscale on transparent glass materials has been demonstrated by the data-driven UPS laser processing.

This keynote presentation addresses the advantages, recent developments, and perspectives of laser processing with ultrashort laser pulses. A special focus is laid on the tailored structuring of thin films as well as the manufacturing and probing of sub-diffraction surface nanostructures – an ongoing race to extreme scales. Current limitations are identified and an outlook to future scaling perspectives will be provided.

High repetition rate femtosecond lasers are commonly used for fabricating laser-induced periodic surface structures (LIPSS) over large areas at high processing speeds. Industrially relevant metals, like steel, experience thermal modifications at repetition rates beyond several hundred kilohertz. In this work, we fabricate low spatial frequency LIPSS (LSFL) on steel, varying pulse repetition rates from 10 kHz to 2 MHz. The study characterizes laser-structured areas and redeposited debris using SEM and μ-Raman spectroscopy. A simple heat dissipation model identifies repetition rate ranges associated with thermal modifications. Morphological changes and debris impact functional wetting behavior, offering insights for optimizing parameters in high repetition rate femtosecond laser materials processing.

External pulse compression offers the possibility to shorten the pulse duration of industrial grade femtosecond lasers from 300 to 500 fs well below 100 fs with an efficiency of typically 90%. We nvestigated the sub 100 fs regime for industrial laser micromachining processes. We show first results of a parametric study on ablation efficiency varying the pulse duration over 2 orders of magnitude, from 57 fs to 5 ps. We further characterize the micro-processing quality in terms of the surface roughness and the minimum achievable structure size for metals, semiconductors and glasses with an industrial grade Carbide laser from Light conversion at a wavelength of 1030 nm in combination with MIKS1 S pulse compressor from N2 Photonics (offering sub 100 fs pulses) and a high end Excelliscan galvo scanner from Scanlab for repetition rates from 80 kHz up to 1.2 MHz.

Femtosecond laser welding of glass has numerous advantages, such as high mechanical resistance and high temperature tolerances without adding new material. In this context, an innovative way to join glass using a long focal lens of 100 mm has been developed. The advantages of using such a lens are clear: a drastic diminution of the thermal gradient and a slow thermal accumulation allowing crack free joining thanks to the larger focal volume, and a more robust process thanks to the long Rayleigh length. The study of the thermal accumulation process will be presented.

Laser printing with structural colors arising from nanostructure-light interaction is emerging as a promising technology to address the problem of toxic compounds in conventional coloration methods. Up to date, the best-performing laser coloration techniques rely on ultrafast pulsed lasers. In this work, we introduce an approach for low-power, wide-gamut laser coloration on a pre-processed metamaterial of self-assembled nanoparticles. The metamaterial, with aluminum-coated polystyrene nanospheres, changes color through oxidation layer and deformation shape control, achieved using a focused CW laser with an average power of 10 mW. This approach achieves a 33k DPI resolution on a flexible substrate with the broadest color gamut reported.

Ultrafast higher-order Bessel beams have diverse applications, including creating high aspect ratio nanovoids and efficient glass cutting. This study introduces a novel method using higher-order Bessel beams to generate high-aspect ratio nanostructures vertically standing on sapphire with a single ultrafast laser pulse. The elongated nano-pillars exceed 15 μm in height and possess a sub-micrometer diameter. We propose a mechanism that explains the different generation regimes. Depending on deposited energy density, either material translation or hydrodynamics occur and produce different morphologies. Our conclusions are supported by transmission electron microscopy. This approach, applicable to various transparent materials, stands out for its simplicity and deepens understanding of ultrafast laser-material interactions, holding potential for advanced material processing.

Recently, the ultrafast Bessel beam has emerged as an efficient tool to structure nano-volumes in sapphire crystals with a high aspect ratio of more than 100. To increase the controllability of the process, there is a quest to understand better the interaction of ultrafast Bessel beams with sapphire in intensity ranges pertinent for nanostructuring. In the present study, we investigate the ultrafast interaction of a short-pulsed Bessel beam with a single-crystal sapphire sample using time-resolved phase contrast and quantitative phase contrast microscopy techniques. The time-resolved relaxation dynamics reveal that the plasma phase in sapphire persisted for the duration of a few ns followed by the tens of ns long hot phase that triggers amorphisation. Around 100 ns the manifestation of nano-volume expansion becomes visible. This study contributes to attaining precise control in the laser processing of sapphire for scientific and industrial applications.

Over last decade, ultrafast lasers became industrially viable tool for high precision material processing. Ability to modify in the bulk of transparent materials is one of unique attributes of this technology. This have been successfully used for glass cutting, implementation of photonic circuits and microfluidic chips, local engineering of optical fibre properties. This talk will explore how ultrafast lasers can be used to engineer optical scattering systems. The exploitation of this process for developing low loss distributed sensing systems and compact optical spectrometer will be discussed and demonstrated.

In recent years, Volume Bragg gratings (VBGs) have seen widespread use, traditionally inscribed in photo-thermo-refractive glasses. The emergence of femtosecond lasers has enabled VBG inscription in various materials. Silver-containing glasses have drawn attention due to their ability to produce strong Type-A (“A” for Argentum) refractive index changes. We explored the laser writing processes for optimizing the recording inscription of Type-A VBGs. The Gaussian-Bessel beam is employed to produce a single plane grating with 6700 µm3/s throughput while the phase mask approach is investigated to accelerate VBG inscription, allowing record throughput up to 106 µm3/s, paving the way for industrial applications.

We introduce a single-mode Erbium-doped master oscillator power amplifier (MOPA) fiber laser, capable of directly generating 100 fs pulses at 2.2 W and 120 fs pulses at 4.5 W of average power. This laser operates at a pulse repetition rate of 1.2 GHz with a repetition rate multiplier, at the central wavelength around 1550 nm. The laser system comprises a passively mode-locked oscillator with a repetition rate of 77.6 MHz and an average power of 16.3 mW followed by a repetition rate multiplier and a cladding-pumped co-doped Er-Yb fiber laser. 100 fs long pulses, as the shortest pulse duration, was directly achieved at an output power of 2.2 W. In this experiment, the pulse dynamic at different output powers has been studied and verified by simulation. This developed system is employed in micromachining and sub-surface silicon processing at low pulse energy at a GHz-range repetition rate.

Our study introduces a new method for label-free super-resolved polarimetry on nanomaterials, compatible with in-situ analysis. Integrating Image Scanning Microscopy (ISM) with polarimetry techniques, we achieve remarkable resolutions down to 90 nm while acquiring polarization information. Overcoming limitations associated with fluorophores in challenging materials, our approach facilitates quantitative measurements of optical properties. Applied successfully to nanostructured surfaces created by femtosecond lasers and boron nitride nanotubes, our work showcases the versatility of this methodology.