This PDF file contains the front matter associated with SPIE Proceedings Volume 10519, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

The recently reported copper ablation study using ultrafast IR lasers with unusually high burst repetition rates (∼ GHz) that claims “an order of magnitude” efficiency enhancement compared to non-burst processes due to “ablation cooling” warrants further investigation both experimentally and through modeling the process. We experimentally reproduce a subset of these results, compare it to the known best non-burst pulse results, and find that within our experimentally accessible parameter range, there is indeed an up to ∼ 3.5x benefit when punching (i.e. drilling holes) with 864 MHz pulse bursts. However, this efficiency increase does not translate from punching to milling (machining an area), which we find to be less than half as efficient as an optimized non-burst process, while also delivering worse process quality. We conclude that a hydrodynamic picture is needed to understand the discrepancy between punching and milling efficiency for a ∼ GHz burst process.

In the burst mode the reported removal rates were often higher than the ones achieved with single pulses at identical repetition rate and average power. But this effect is mainly caused by the reduced energy per single pulse in the burst and the corresponding fluence which is then nearer its optimum value showing highest specific removal rate. But there exist special situations where the burst mode shows a higher efficiency and therefore an increased specific removal rate. For copper e.g. it was found that a 3-pulse burst with a time spacing of 12 ns at a wavelength of 1064 nm leads to an about 15% higher specific removal rate. We extended the burst investigations to semiconductors and isolators and measured the specific removal rate as a function of the applied peak fluence for different materials, number of pulses in the burst and time spacing. For 1064 nm silicon e.g. shows a maximum specific removal rate which amounts about 1.7 µm3/µJ for single pulses and a 2 pulse burst as well. Then it almost linearly increases up to about 5 µm3/µJ when the number of pulses in the burst is raised to 8. A similar effect is found for machining grooves into diamond-like nanocomposite films with single pulses and a 2- and 3-pulse burst, respectively. In contrast, for silicon and 532 nm wavelength where the photon energy exceeds the bandgap, only a small difference in the maximum specific removal was observed. Heat accumulation is assumed to cause the higher specific removal rates but further experiments are needed gain a clearer picture.

The today available ultra-short pulsed laser systems offer average power in the range of 100 W or even more resulting in high pulse energies. In contrast to treat metals only moderate peak fluences are required to work at the well-known optimum point, where the ablation process is most energy efficient. In a standard setup the laser beam is deflected by a galvo scanner. The achievable scan speed is limited and therefore also the usable repetition frequency and average power. The use of pulse bursts instead of single pulses is a possibility to further increase the ablation rate, i.e. using higher average power. This further increase is crucial for the usage of the ultra-short pulses in industrial applications. It was shown in previous publications that the number of pulses in the burst have a significant influence on the specific removal rate in case of ps pulses. It was observed, that the second pulse of a 2-pulse burst is shielded by the particle plume of the first pulse of the burst. It is believed that the shielding effect depends on the particle density of the plume, thus the effect should be stronger if more material is ablated. As already known, a decrease of the pulse duration to a few hundreds of fs leads to an increase of the specific removal rate for single pulses. In this work we investigate the influence of pulse bursts on the specific removal rate as well as the pulse duration on the ablation process using pulse bursts.

The welding of transparent materials by ultrashort laser pulses has gained particular interest in recent years. While the short pulse duration enables to locally modify glasses within the bulk, high pulse repetition rates facilitate to accumulate heat from pulse to pulse leading to local melting. After resolidification strong covalent bonds are formed providing high stability of the joined partners without the need of additional material such as glue. In particular dissimilar glasses can be welded with breaking strengths in the range of the volume material while the weld seams are gas dense and long term stable.

However, industrial applications demand for enhanced throughput. Scaling the process speed requires advanced concepts for temporal and spatial tailoring the laser induced heat. By using short laser pulse trains, so-called bursts allows to reduce or redistribute the induced stress and hence increase the breaking strength of welded samples in the range of the volume material. Besides the laser parameters used, also the surface quality and eventual gaps denote a decisive issue for laser welding under industrial conditions. In this framework time-resolved pump-probe measurements are used to analyze the evolution of weld seams, in particular the melt transfer in between the samples facilitating process development. By extending the time-resolved pump-probe setup with polarization optics even allows for quantitatively investigating laser induced stress which serves to optimize the achievable breaking strength.

The context of future laser applications in modern manufacturing can be summarized by Digital Photonic Production (DPP). “From Bits to Photons to Atoms” describes the vision of DPP: Designing a component or product in the computer and creating it directly by additive or subtractive photon based processes or production-systems.

Despite of today’s availability of high power USP lasers up to several hundred Watts, it is still a challenge to structure large surface areas as required on printing and embossing rollers within an acceptable processing time for industrial production. This paper shows and compares the results of two different approaches, the parallel treatment of the workpiece with multiple beam arrangements (each beam individually modulated at repetition rates of up to 2 MHz) and a second approach based on high pulse repetition rates from 6 MHz to 16 MHz combined with fast beam scanning techniques with a polygon scanner up to 100 m/s.

Nowadays the relevance and the robustness of ultrafast lasers are well established for many industrial applications. Indeed this laser technology combines the unique capacity to process any type of material with an outstanding processing precision and a minimal heat affected zone. The key issue is to combine high throughput, low residual thermal load and good processing quality. Thanks to high average power and high repetition rate it is possible to achieve high throughput providing that the operating parameters are precisely tuned to the application, otherwise heat accumulation and heat affected zone may appear, leading to detrimental effects such as burr, uncontrolled melting and metal oxidation. In this paper we report on high-throughput laser ablation of metals using a 100W- and 10MHz- ultrafast laser. Target materials were stainless steel, Copper, and Aluminum. Operating parameters such as fluence, repetition rate and scanning velocity have been considered. Results are discussed in terms of ablation efficiency, surface morphology, multipass and upscaling capabilities. Different behaviors between materials are also discussed. We observe that pulse-to-pulse pitch and delay are key parameters that must be taken into account in order to define relevant process windows for each material. The use of polygon scanner instead of galvo scanner enables us to reduce the thermal load along the laser trajectory. The point is not to avoid heat accumulation but to take advantage of this phenomenon as long as the target material can stand the thermal load without detrimental effects on the processing quality.

Fiber beam delivery of high power pico- and femtosecond pulses offers many advantages in industrial application. This includes flexible beam delivery, easy integration into machines and production environment as well as laser safety and robustness. Using micro-structured hollow core fibers nearly single mode transmission of ultra-short pulses with excellent beam quality can be achieved over several meters and has been reported in numerous publications during the last couple of years. Laser light cables and beam delivery systems with these fibers are now available and capable of delivering pulses of several 100 μJ with 90% transmission over 10 m long fibers while maintaining excellent beam quality (M2 1.2 - 1.4). For successful industrial application, several additional factors need to be taken into account. This includes system robustness against changing laser input parameters as the output of a laser source can change, robustness against fiber bending in applications with dynamically moved fiber as well as operation free of maintenance and realignment. In order to address these, the relevant effects impacting the performance of fiber delivered laser pulses have been studied. We will report experimental results of fiber bending effects on beam parameters critical for micromachining applications and analyze the influence of laser to fiber coupling. In addition, micromachining applications employing a modular fiber beam delivery system will be shown and the impact of induced beam parameter changes on the micromachining process discussed.

The characterization of surfaces using photoelectron spectroscopy or photoemission electron microscopy provides sensitive probes of surface structure and electronic properties. Conventional extreme ultraviolet (XUV) light sources used for photoemission do not have ultrafast time resolution, which inhibits applying these techniques to the study of surface dynamics on their natural time scale. The high harmonics (HHG) of intense femtosecond laser pulses are capable of providing ultrashort XUV pulses for photoemission. However, for pulse-based photoemission measurements it is necessary to limit the density of electrons emitted by each pulse to prevent detrimental spacecharge effects. Therefore, to maintain reasonable data acquisition rates, the pulses must occur at a high repetition rate. Since the HHG process requires high peak fundamental laser powers, repetition rates have typically been limited to well below 1 MHz.

In our lab, we can perform time-resolved XUV photoemission experiments at an 87 MHz repetition rate using a cavity-enhanced HHG source. Harmonics are generated at 87 MHz by resonantly enhancing a Yb:fiber laser capable of 1 μJ pulses in a passive optical cavity to pulse energies > 100 μJ. Average photon fluxes of up to 7x10¹¹ photons/s in a single isolated harmonic are delivered to a surface science end station. This delivered flux and repetition rate are comparable to a synchrotron light source, but with pulse durations nearly 1000 times shorter. In this paper, we discuss critical details of the source and its performance.

Micro structuring of transparent materials with ultra short pulsed laser radiation is nowadays an established and widely used processing method. However, process optimization, such as the reduction of cracks and defects as well as achieving an increased throughput, remains a challenging task. A general approach requires a detailed knowledge of the underlying mechanism of the laser material interaction. For this purpose, in-situ microscopy offers comprehensive insight into the spatial and temporal characteristics of the nonlinear absorption and subsequent thermalization or relaxation phenomena, respectively.

To pursue this approach and analyze various damage mechanisms in a subtractive micromachining process, we apply a novel pump probe microscopy setup, which enables us for the first time to examine an extended parameter range. We present in-situ data of the nonlinear interaction region in glass on a micrometer scale with a temporal resolution of approximately 200 fs comprising the laser material interaction from femtoseconds to microseconds. Our investigations are carried out for incubation and accumulation processing regimes up to a repetition rate of 1 MHz. Additionally, pump pulse durations between 300 fs to 20 ps, as well as several burst operation modes are accessible with our experimental setup. Our extensively automated pump probe setup enables us to reconstruct the material extinction response to analyze the complex absorption profiles. In this context, we report on flexible processing strategies and exemplarily processing results.

We are going to present an iterative Fourier transformation algorithm (IFTA) based computation-method for Phase retrieval of beam splitter elements. The power distribution between the separate beamlets will be controlled via a camera feedback loop in order to create an output distribution which is more closely fitted to the desired distribution than by solely virtual computation. It is taken into account, that by doing so the computation time will rise. Furthermore, we will show some parallel micro structuring examples with femtosecond laser beams utilizing this algorithm. All experiments will be conducted with imaging close to the resolution limit.

Extensive research efforts are currently devoted to alternative materials for photovoltaic (PV) applications that can overcome issues of the currently dominating thin film solar cell technologies, namely, such as CdTe and Cu(In, Ga)Se2 (CIGS). In this context, the kesterite compound Cu2ZnSn(S,Se)4 (CZTS) containing earth-abundant and non-toxic elements, as well as an optimal direct bandgap at 1.5 eV, is a promising candidate for PV applications. However, the efficiency of CZTSSe of 12.6% achieved today is still below the ultimate goal of >20% efficiency. In particular, the synthesis of CZTS is rather challenging due to its relatively narrow phase region and good control of the composition is critical for obtaining high performance solar cells. In this paper, we will discuss the synthesis of the quaternary CZTS compound by pulsed laser deposition (PLD). We will present different approaches for the deposition of CZTS: 1) room-temperature deposition followed by post-annealing and 2) growth of CZTS at high temperature. In the former approach, a sulfur evaporation beam assisting the deposition of CZTS is used to compensate for the sulfur loss. Our findings reveal that during ablation of a multicomponent CZTS target, the stoichiometry of the films can vary dramatically from a fluence from 0.2 J/cm2 to 2 J/cm2. In particular, films deposited at a low fluence of 0.2 J/cm2 are Cu-free, and the Cu content in the films increases monotonically with increasing fluence. Interestingly, this effect is less pronounced for ablation of a single-phase CZTS target.

Addressing the need for fast design cycles and tooling in the assembly of small structures, a flexible approach to overcome the obstacles of current time-consuming manufacturing methods is needed. Additionally, assembly of small and especially optical structures is often limited concerning the application and curing of adhesives used for joining. Local heating structures can be seen as an ideal way of solving this issue. This paper shows the simulation and flexible laser structuring of miniaturized heating. Mask-based large panel physical vapor deposition (PVD) processes and subsequent laser processing appear to be economical and flexible, and are compared to standard panel level lithography processes.

In this work, a two-section wavelength tunable laser diode is demonstrated using an InGaAsP multiple quantum well heterostructure. The laser diode consists of two sections with different bandgap energies achieved using selective area intermixing of the MQW. Using plasma enhanced chemical vapor deposition (PECVD), half of the sample is coated with a 30nm silicon nitride (SiN_x) film followed by a 200nm thick overlay of silicon oxynitride (SiO_xN_y) film over the entire sample. The whole sample is then thermally annealed at 750°C for 30s, and that results in the SiO_xN_y covered section experiencing a narrowing of the bandgap energy, while leaving the SiN_x covered section practically unchanged. A laser stripe is fabricated that passes through both MQW sections. The wavelength of laser operation can then be tuned by varying the injected current levels applied separately to the two sections. The obtained tuning range was 40 nm spanning from 1538 nm to 1578 nm.

This paper describes digital printing of optical metasurfaces, by holographic laser post-writing on nano-textured, metal-coated template surfaces. Holographic laser printing with a spatial light modulator (SLM) provides multiple pixel exposure and high power endurance, where individual template nano-stuctures are thermo-optically modified by resonant absorption. Ultra-high printing resolution, beyond 100,000 Dots per inch (DPI) is achieved - enabling nano-scale digital laser printing for mass customization of optical components and individualized decoration of consumer products. We present laser printed structural colors and flat optics components, such as Fresnel Zone Plates (FZP) and Axicons.

INVITED (by Beat Neuenschwander) An important challenge in the field of three-dimensional ultrafast laser processing is to achieve in the bulk structuring of silicon and narrow gap materials. Attempts by increasing the energy of infrared ultrashort pulses have simply failed. Our solution is inspired by solid-immersion microscopy to produce hyper-focused beams which are intrinsically free from aberrations and associated with an extreme energy confinement deep into the matter. Its validity is demonstrated by controlled refractive index modifications inside silicon. This opens a way to the direct writing of 3D monolithic devices for silicon photonics and provides perspectives for new strong-field physics and warm-dense-matter experiments.

The laser inscription of waveguides into the volume of crystalline silicon is presented. By using sub-ps laser pulses at a wavelength of 1552 nm highly localized light guiding structures with an average diameter ranging from 1 – 3 μm are achieved. The generated waveguides are characterized in terms of mode field distribution, damping losses and permanent refractive index modification. First investigations indicate an induced increase of the refractive index in the order of 10^-3 to 10^-2. Depending on the applied laser pulse energy single-mode to multimode like propagation behavior can be observed. At optimized processing parameters, the damping losses can be estimated below 3 dB/mm.

Molybdenum disulfide (MoS₂) films have attracted a great deal of research interest due to the unique properties of films when the thickness is a few atomic layers: Previous work in the literature has shown high field-effect mobility (comparable to graphene), and a large direct bandgap (around 1.8 eV), along with a high strain limit (~10%). We demonstrate a complex multi-laser process scheme based on a direct-write system – comprised of co-incident pulsed and CW lasers where each laser amplitude is modulated to a predefined script for precise control of laser doses. The arrangement enables tuning the properties of a sputtered MoS₂ thin film.

We focus on properties which are expected to be of use in flexible electronics and chemical sensing device applications. First, we demonstrate the process for inducing crystallinity from the amorphous phase and reducing the layer thickness down to the regime of several monolayers. Second, we measure electrical conductivity using both pure sputtered MoS₂ films and films co-sputtered with small amount of gold (<20%). Third, we measure the wettability of the processed surface, as measured by droplet contact angle. The measurements compare the properties under different processing conditions.

Laser induced forward transfer (LIFT) technique has been used for printing of various materials ranging from flexible metallic contacts to conductive silver lines. In this study, we are focusing on the printing of an industrial-grade silver paste formulated for the metalization of the front side of solar cells. Printing of industrial silver pastes using the LIFT technique is challenging because the high viscosity of the silver paste allows only a small window of process parameters for reproducible and well-defined material transfer. In this work, we are examining the multiple-pulse effects during the printing of silver paste. Time-resolved imaging and characterization of the ejected silver paste voxels are performed to examine the influence of process parameters on the morphology of transferred paste dots and lines. We have observed that by firing repeating laser pulses below the transfer energy threshold it is possible to print smaller volumes of paste, which yields an opportunity to print lines with higher resolution. We also show that it is possible to print well-defined dots (voxels) of the paste using pulse energies near transfer threshold values. However, regarding the printing of lines, there is a strong interaction effect between adjacent voxels. This influence is so important that a distance between adjacent laser pulses threshold has been evaluated to print lines. The printing of single voxels has been achieved above the evaluated threshold value, while no printing could be achieved below the threshold. This distance threshold represents a limitation to the LIFT process of high viscosity pastes, which indicates that a compromise must be done between voxel size and laser frequency.

For high quality film printing, we have newly developed a laser-induced forward transfer with optical stamp (shortly, LIFTop), that consists of a two-step transfer process. In the first step, functional films were transferred onto a transparent polymer having high adhesiveness and elasticity like PDMS, which we call “optical stamp”. This stamp helps to avoid the transferred film from pattern spread and fracture. Then, the transferred micro-pattern on the optical stamp was further transferred onto a final target. In this talk, metal and transparent conductive oxide film transfer was demonstrated using our new LIFT process.

Ultrashort laser pulses generate free electrons in dielectrics and thus enable the absorption of laser energy. The electron density is a crucial parameter here, but also the energy distribution of the excited electrons plays a remarkable role. We calculate it in detail with help of full Boltzmann collision integrals. Here, we show a standard example of the evolution of the distribution function of electrons in valence- as well as in conduction band, and analyze the influence of different collision processes. The energy distribution can deviate from a Fermi distribution for several hundreds of femtoseconds, driven by an interplay of secondary ionization processes and the cooling by the lattice. We study in detail these relaxation processes and discuss their mutual influence.

Ultrafast light coupling with metal surfaces shows strong potential for nanostructuring applications relying on the capacity to localize light energy on the nanoscale. Controlling light confinement requires to understand the transient variation of the optical response during ultrafast irradiation. The fundamental approach we propose based on ab initio calculations allows elucidating the influence of electron-phonon nonequilibrium on optical properties. This results from the investigation of the primary processes responsible for the optical change during laser-solid interaction. Calculations are carried out in the framework of the density functional theory associated to quantum molecular dynamics. Our results shed light on the intricate role of electronic structure modifications and possible optical transitions, driving the laser energy absorption into the material. The revealed key processes based on Fermi smearing on an evolving density of states are of paramount interest for controlling laser energy deposition, surface plasmon excitation and subsequent surface nanostructuring. The calculations predict the possibility of an ultrafast laser-driven plasmonic switch on a typically non-plasmonic material (W), confirmed by pump-probe ellipsometric measurements [1]. The consequence of our results is far reaching as they propose also a route for achieving the highest energy confinement under ultrashort laser irradiation. [1] E. Bévillon, J.P. Colombier, V. Recoules, H. Zhang, C. Li, R. Stoian, “Ultrafast switching of surface plasmonic conditions in nonplasmonic metals”, Physical Review B 93 (16), 165416 (2016).

When a silver sample is irradiated with an ultrashort laser pulse with a wavelength of 400 nm and 800 nm, at first only the electronic system is excited. They are driven out of equilibrium, i.e. they do not follow a Fermi-Dirac distribution directly after excitation. We calculate the transient distribution function with help of full Boltzmann collision integrals. We show the influence of laser parameters like wavelength and fluence on the initial electron nonequilibrium distribution, as well as on the thermalization process. We find an strong dependence of the excited electron distribution on characteristic features in the electronic density of states.

Femtosecond laser written devices inside a smartphone screen, in this case Gorilla Glass ®, have been recently demonstrated1 with a high potential of increasing the functionality of cellphones, consuming minimal space using the glass screen2. Even though low loss waveguides have been reported in this glass, the behavior of the refractive index of the glass subject to femtosecond laser radiation is not well understood. Here, we propose a study of that behavior by presenting the identification of two major transitions where the induced refractive index seems to decrease. The first transition occurs at lower fluence and is characterized by a single structure while the second one occurs at much higher fluences, and is well characterized by a double shell structure. In both these transitions, the refractive index at the center of the structure seems to decrease. However, it should be noted that between these two regimes, there is narrow regime in which light seem to be guide in the middle of the fs processed region, confirming the possibility of making a single pass waveguide. The fluence limits of each regime has been investigated as has the quality of the waveguide made by a single and multi-passes. The refractive index of the affected zones is mapped by a highly sensitive phase-interference technique. [1] Lapointe, J., Gagné, M., Li M.J., and Kashyap R., "Making smart phones smarter with photonics," Op. Exp., Vol. 22, No. 13, pp. 15473-15483, (2014) [2] Lapointe, J., Parent, F., Soares de Lima Filho, E., Loranger, S., and Kashyap R. "Toward the integration of optical sensors in smartphone screens using femtosecond laser writing," Optics Letters, Vol. 40, No. 23, pp. 5654-5657, (2015)

Calcium Fluoride (CaF2) was identified among the first host crystals for active laser media. However, due to the need of charge compensation of Nd3+-doped fluorite crystal structures, other host materials like YAG, oxide and fluorite glasses were preferred over the years. Recent developments made on ytterbium-doped alkaline-earth fluorides have shown that it is possible to have better scalability of crystal growth, very high thermal conductivity, high laser-induced damage threshold, longer emission lifetime, lower nonlinear refractive index and large emission wavelength tuning range. Due to these reasons, Yb-doped CaF2 has once again proved to be a competitive material for high-energy and high-power operations. Waveguides confine light propagation resulting in reduced lasing thresholds and enhanced laser efficiencies. By properly managing the three-dimensional translation of the focal volume of pulsed lasers, it is possible to create waveguides and other 3D structures inside crystals. Recently, depressed cladding waveguides written inside CaF2 were reported. In this work, we will present the first, to the best of our knowledge, double track waveguides inscribed inside doped and undoped CaF2 crystal with different pulse energies. Waveguide characterization, determination of mode-field diameter, analysis of polarization dependent guiding and also direct refractive index change measurements of the waveguides were performed and will be presented. Additionally, single pass gain and lasing experiments will be demonstrated both theoretically and experimentally.

The generation of intra-volume modifications and mechanical separation is a highly efficient two-step glass cutting approach. The high aspect ratio modifications, required for thick glass cutting, can be obtained by utilizing Bessel-like beams, which have a long non-diffractive length with a small quasi-propagation-invariant central core. Usually, laser-induced modification channels have to be tightly spaced to achieve a predictable glass separation. However, we demonstrated that cutting speed and glass cleavability may be significantly enhanced by introducing aberrations to the generated beam. Glass cutting experiments were carried out using the fundamental frequency of the DPSS laser Atlantic HE (from Ekspla), which delivered 300 ps pulses of 2 mJ energy at 1 kHz repetition rate. The incident Gaussian beam was reshaped to the Bessel-Gaussian beam using a conical lens and a 4F optical demagnifying system. A 4-point bending setup was used to separate glass sheets and to evaluate the processing regimes. We have found that the used conical lens deviated from an ideal cone shape and had two often occurring manufacturing defects - the oblate-tip and elliptical cross-section. As a result, the generated beam had the on-axis intensity modulations and asymmetrical intensity distribution in the XY plane, which induced transverse cracks in the bulk of glass, which were extended along the major axis of an ellipse-shaped central core of the beam. Laser-induced transverse cracks in combination with high aspect ratio modifications were applied for fast cutting of the 1 mm-thick glass. Results were compared to glass cutting using the symmetrical Bessel-Gaussian beam.

Polydimethylsiloxane (PDMS) is a material used for bio-chips and micro total analysis systems / lab-on-chips. For further development, it is inevitable to develop a technique to fabricate precise structures on micrometer scale at high aspect ratio. In the previous works, we reported a technique for high-quality micromachining of PDMS sheets, by means of ablating the PDMS sheets using EUV radiations around 10 nm from laser-produced plasma. In the present work, we have investigated fabricated structures based on wave optics, for fabricating designed strutures at submicrometer precision at high aspect ratio up to 10. We experimentally found that a deep hole with a diamter of 100 nm is formed at the center of flat ablated region after EUV irradiation of a PDMS sheet through a circular aperture with a diamter of two micrometers in a contact mask. In the case of EUV irradiation through square apertures, the deep hole was not found on a PDMS sheet, while narrow dip is formed at the edge of the ablated region. We numerically calculated propagations of EUV plane wave light in PDMS sheets. After traveling one micrometer from a circular aperture, an intense peak appears at the center of the beam, which is caused by diffraction. For the square apertures, the enhancement does not occur, while intense profile near the edge is formed due to the Fresnel diffraction. Interestingly, at 100 micormeters from the aperture, the Frenel peaks are superposed at the center, resulting in a narrow and intense beam.

In this paper, the micro-processing of glass, sapphire, and polymers using industrial-grade nanosecond (ns), picosecond (ps), and femtosecond (fs) lasers was reported. Square/round inner contour were fabricated in glass and sapphire (0.3 to 1.1 mm in thickness) by the ablation-based cutting method using the ns, ps and fs lasers. The chipping sizes were 20 – 50um with 532nm ns laser, < 10 with 1064nm ps laser, and < 5 μm with 515nm fs laser, respectively. When processed using the 532nm ns laser, the laser fluence is 5 – 10 times higher than that used in the ultrafast lasers. Outline-dicing of glass, and sapphire was conducted using a 1064 nm ps laser followed by thermal/mechanical breaking. The laser beam was shaped to form a long focal depth. Clean edges and cross-sections were observed on the processed transparent materials. Melting-free cutting of PI, and PLLA was successfully realized using a 515nm fs laser to fabricate printable electronic and medical devices. The impact of the key parameters, including pulse energy, repetition rate, focal spot size, beam shaping was systematically studied. The best ablation efficiencies of glass and sapphire obtained were 0.3 - 0.4mm³ /(W•min.) when using the ultrafast lasers, which is much lower than that of polymers (2.0 – 4.0mm³ /(W.min).).

Three-dimensional (3D) laser lithography has become a versatile, reliable, and widespread workhorse for fabricating 3D micro- and nanostructures. I will illustrate the current state-of-the-art by selected examples. I will emphasize our work on 3D functionalized micro-scaffolds to steer the growth of cells, 3D metamaterials with negative effective static volume compressibility, and 3D chiral micropolar mechanical metamaterials that can be seen as the counterpart of optically active materials.

Three-dimensional printing on the micro/nanoscale is well known to be possible through the use of ultrafast, pulsed lasers taking advantage of a nonlinear multi-photon absorption effect. The feature size and resolution of this technique, often referred to as 2-photon polymerization (2PP), is greatly determined by the individual three-dimensional printing pixel size, called a voxel. Determination of this important feature of fabrication has been primarily explored through experimental means, however numerical models have been developed for the propagation of a single laser pulse through transparent materials, such as fused silica. In this work, a (2+1) spatiotemporal model is applied to a femtosecond laser pulse at 800nm wavelength propagating through a transparent photoresist. This model takes into account the effects of laser beam diffraction, group velocity dispersion, self-focusing, defocusing, and absorption due to the free electrons and nonlinear photoionization of the valence electrons. Using calculated energy flux and free electron density an absorption profile is determined allowing the prediction of the threshold of polymerization and giving insight into the voxel size. This prediction is then verified experimentally through single pulse experiments and voxel size measured using scanning electron microscopy and atomic force microscopy.

There have been extensive research on micro/nano additive manufacturing methods employing laser (or optical) and ion/electron beams. Many of these processes utilize specially designed photosensitive materials consisting of additives and effective components. Due to the presence of additive (such as polymer and binders), the effective components are relatively low resulting in high threshold for device operation. In order to direct print functional devices at low cost, there has been extensive research on laser processing of pre-synthesized nanomaterials for non-polymer functional device manufacturing. Pre-synthesized nanocrystals can have better control in the stoichiometry and crystallinity. In addition, pre-synthesis process enjoys the flexibility in material choice since a variety of materials can be synthesized. In this paper, we report femtosecond laser assembly and deposition of nanomaterials for 3D micro/nano additive manufacturing. The laser-nanomaterial interaction and nanomaterial transport under laser excitation and modification are studied. A scheme to directly printing functional nanostructures was demonstrated by laser excitation of gold nanocrystals. The scheme paves the way for laser selective electrophoretic deposition as a micro/nanoscale additive manufacturing approach.

We have succeeded in synthesizing zinc oxide (ZnO) microspherical crystals and Silicon microspheres by a simple laser ablation technique in air, and demonstrated whispering-gallery-mode (WGM) lasing from optically-pumped ZnO microsphere. ZnO/MgO alloy microspheres were also successfully fabricated, and blue-shift of WGM lasing wavelength was achieved. Recently, size-controlled and on-demand fabrication of semiconductor microspheres by introducing of an optical vortex beam.

Molding technologies are mostly employed to fabricate microneedles (MNs) for medical and cosmetic applications, such as drug delivery and skin care systems. However, such technologies are ill suited for bioabsorbable materials with high viscosity, thus, there is no report concerning hollow bioabsorbable MNs, so far.

We propose a novel laser processing technology, which enables us to fabricate a hollow bioabsorbable MN by simply irradiating both optical vortex for fabricating MNs and Gaussian beam for drilling holes on a hyaluronic acid sheet.

Networks of metallic nanowires are promising candidates for transparent and flexible electrodes, as alternatives to metal oxide based electrodes such as indium tin oxide (ITO). Such nanowire electrodes can have excellent performance, however, the mechanical and chemical stability of the electrodes are usually week. Here, we report a simple method for fabricating transparent and flexible gold electrodes that have excellent mechanical and chemical stability. Gold nanoparticles were synthesized and subsequently aggregated by adding sodium hydroxide into the solution. The aggregated nanoparticles were deposited on a polycarbonate (PC) filter membrane followed by flash light sintering (FLS). By using this method, transparent and flexible gold electrodes were produced, with electric properties found to be stable under mechanical treatment such as folding, peeling and rubbing and under chemical treatment such as water, ethanol, nitric acid and sodium hydroxide. A nanosecond pulsed (7-9 ns), solid state laser (SSL) at 355 nm coupled to a galvo-scanning mirror system was used for laser assisted processing (patterning and ablation) of the gold nanoparticle thin films to further increase the transparency. By careful evaluation of laser (pulse energy, repetition rate etc.) and scanning parameters (speed, pitch etc.) a resolution better than 10 um could be realized by this laser scanning system, which are used to optimize the transmission and conductivity of the FLS gold nanoparticle layer. It is found that this method have potential to produce mechanically and chemically stable electrodes with transmittance over 90% and sheet resistance less than 100 Ohm/sq.

Heavy metal pollution in developing countries urgently becomes a serious environmental issue due to rapid industrial development. Therefore, to detect the trace of heavy metal ions in water and food is very critical for environmental governance and human health. Surface-enhanced Raman scattering (SERS) based on electromagnetic field extraordinary enhanced in the proximity of metal nanostructures can generate strong Raman scatting, which is an effective method for trace detection. Most of SERS devices have been fabricated on the solid substrate surfaces, while detection of toxic substances in the close environment is much more preferable. In this paper, we propose the novel technique that can create 2D periodic metal (Cu-Ag) nanostructure inside 3D glass microfluidic channel by all-femtosecond-laser-processing. Specifically, after fabrication of 3D glass microfluidic channel by femtosecond laser assisted wet etching, Cu-Ag thin films are formed inside the microfluidic channel by femtosecond laser selective metallization. The thin films are then 2D nanostructured by femtosecond laser induced periodic surface structure (fs-LIPSS) formation. The dimension of nanostructured Cu-Ag film is quarter of laser wavelength. By testing with rhodamine 6G, we demonstrate the fabricated microchips can be used as a sensitive SERS device with an enhancement factor larger than 10⁷ and 8.8% relative standard deviation. Consequently, the Real-time SERS detection in microfluidic chips was successfully demonstrated, which verified capability of the fabricated microchips as an excellent microfluidic SERS platform with ultrasensitive and uniform enhancement.

We present the surface microfabrication of CYTOP, an amorphous UV transparent fluoric polymer, using a conventional pulsed green laser. Fluorine-based polymers have unique characteristics, including high transparency from the deep-UV to the IR wavelengths, chemical stability and low refractive indices, and thus are expected to have a number of industrial applications. However, CYTOP and other fluoric polymers are generally very difficult to microfabricate unless to use high particle beams. Therefore, we have developed a technique for the crack-free surface microfabrication of a CYTOP substrate based on ablation with a pulsed green laser followed by successive wet etching and annealing. In this work, the fundamental surface characteristics of the fabricated area were investigated. After the surface microfabrication of CYTOP, a three dimensional biochip was fabricated using a conventional PDMS bonding technique to demonstrate that a CYTOP biochip is superior to conventional transparent biochips with regard to the microscopic observation of cell motion.

Poly-methyl methacrylate (PMMA) has been widely used as biomaterial. In order to add a new function to PMMA, we developed a method to form periodic nanostructures on PMMA surface by femtosecond laser irradiation with a wavelength of 800 nm. Since PMMA had a low absorbance of light in the near-infrared wavelength region, it was difficult to form the structures by femtosecond laser irradiation on PMMA surface. We proposed a method that the femtosecond laser was focused on a titanium (Ti) plate surface through a polymer plate. As a result, the depth of the periodic nanostructures was about 70 nm, and the period of it was about 410 nm. A cell cultivation test was carried out on PMMA plate with and without periodic nanostructures. Consequently, although cells (MG-63) on the non-irradiated PMMA plate were spread in a random direction, cell spreading on the PMMA plate with periodic nanostructures occurs along the grooves.

The authors report the fabrication and characterization of passive waveguides in GeO₂–PbO and TeO₂–ZnO glasses written with a femtosecond laser delivering pulses with 3μJ, 30μJ and 80fs at 4kHz repetition rate. Permanent refractive index change at the focus of the laser beam was obtained and waveguides were formed by two closely spaced laser written lines, where the light guiding occurs between them. The refractive index change at 632 nm is around 10^-4 . The value of the propagation losses was around 2.0 dB/cm. The output mode profiles indicate multimodal guiding behavior. Raman measurements show structural modification of the glassy network. The results show that these materials are potential candidates for passive waveguides applications as low-loss optical components.

In this study, a 6N – 5 phase shifting algorithm comprising a polynomial window function and discrete Fourier transform is developed for the simultaneous measurement of the surface shape and optical thickness of a transparent plate. The characteristics of the 6N – 5 algorithm were estimated by connection with the Fourier representation. The phase error of the measurements performed using the 6N – 5 algorithm is discussed and compared with those of measurements obtained using other algorithms. Finally, the surface shape and optical thickness of a transparent plate were measured simultaneously using the 6N – 5 algorithm and a wavelength tuning interferometer.