This PDF file contains the front matter associated with SPIE Proceedings Volume 10522, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

We monitor the configuration of poly-L-lysine proteins using vibrational resonances at 6 µm (1667 cm^-1) by employing a broadband femtosecond solid-state laser for micro-FTIR spectroscopy. This laser system allows for detection of minute amounts of proteins due to a several orders of magnitude higher brilliance compared to standard FTIR light sources such as globars. Thus, absorption signals as small as 0.5% can be detected without averaging, compared to 6.4% using a globar, at a spatial resolution as small as 10x10 µm^2. Our light source is based on a 98 fs, Yb-doped pump laser at 73 MHz repetition rate, providing 2.5 W average power. By pumping a fiber-feedback optical parametric oscillator (ffOPO) and a post-amplifier, signal and idler beams spanning from 1.33 – 2.0 and 2.1 – 4.6 µm are generated. The tuning range is extended to 8 µm by difference frequency generation between the signal and idler beams and can be further extended by using a pump laser with higher output power. At 7 µm excellent long-term wavelength stability with fluctuations smaller than 0.1% rms measured over 9 hours is observed, without applying electronic stabilization. This is due to the combination of a ffOPO with a post-amplifier and is distinctly superior over other systems based on free-space OPOs. Protein sensing is conducted by applying resonant surface-enhanced infrared absorption (SEIRA) spectroscopy, using a single gold nanoantenna. To the best of our knowledge, this is the first demonstration of resonant SEIRA spectroscopy using a single nanoantenna with a laser system as light source.

Stimuli-responsible controlled release of growth factors from a tissue scaffold has gained significant interest for efficient tissue engineering. Laser-triggered methods for the molecular release have the advantage of spatial and temporal controllability. In this study, we demonstrate laser-triggered molecular release from biodegradable polymer microcapsules incorporated in gelatin hydrogel for the aim of efficient tissue engineering. The microcapsules, which fluorescent molecules were encapsulated, were fabricated using a dual-coaxial nozzle system. The microcapsule suspension was mixed with gelatin solution, followed by cross-linking to fabricate a gelatin hydrogel. Femtosecond laser pulses were focused onto the hydrogel to release fluorescent molecules from the microcapsules in the gelatin hydrogel.

We present measurements of light scatter induced by a new ultrafast laser technique being developed for laser refractive correction in transparent ophthalmic materials such as cornea, contact lenses, and/or intraocular lenses. In this new technique, called intra-tissue refractive index shaping (IRIS), a 405 nm femtosecond laser is focused and scanned below the corneal surface, inducing a spatially-varying refractive index change that corrects vision errors. In contrast with traditional laser correction techniques, such as laser in-situ keratomileusis (LASIK) or photorefractive keratectomy (PRK), IRIS does not operate via photoablation, but rather changes the refractive index of transparent materials such as cornea and hydrogels. A concern with any laser eye correction technique is additional scatter induced by the process, which can adversely affect vision, especially at night. The goal of this investigation is to identify sources of scatter induced by IRIS and to mitigate possible effects on visual performance in ophthalmic applications. Preliminary light scattering measurements on patterns written into hydrogel showed four sources of scatter, differentiated by distinct behaviors: (1) scattering from scanned lines; (2) scattering from stitching errors, resulting from adjacent scanning fields not being aligned to one another; (3) diffraction from Fresnel zone discontinuities; and (4) long-period variations in the scans that created distinct diffraction peaks, likely due to inconsistent line spacing in the writing instrument. By knowing the nature of these different scattering errors, it will now be possible to modify and optimize the design of IRIS structures to mitigate potential deficits in visual performance in human clinical trials.

Multimodal label-free optical microscopy for in vivo and in situ imaging of human tissue represents a challenge especially when nonlinear optical techniques are used. One possible solution to address this challenge is the use of specific hand-held and endomicroscopy probes, based on optical fibers, capable to image at the same time the chemical composition and the morphological structure of the tissues. Nonlinear optical imaging techniques, including TPEF, SHG, spectral focusing CARS, combined with spectral domain OCT are capable to give functional, molecular and morphological information. Since nonlinear optical microscopy and SD-OCT require ultrashort pulses to efficiently image the targeted sample, the development of such probes requires specific attention to high peak power and ultrashort pulse delivery at the focal plane. Different optical fiber technologies for femtosecond pulse delivery are experimentally investigated in order to suggest an optical fiber that fulfill at the same time the requirements for above mentioned imaging modalities. We investigated three different approaches that are normally considered for ultrashort pulse delivery: large-mode area (LMA) fiber, hollow-core photonic bandgap fiber and kagome hollow-core fiber from GLOphotonics. We tested this three fibers on our label-free multimodal imaging platform which is capable to simultaneously acquire TPEF, SHG, spectral focusing CARS and SD-OCT. From our investigation, we identify the fiber which better satisfy the requirements of all the above mentioned imaging modalities in terms of dispersion profile and transmission of high energy pulses. Imaging capabilities are shown on a biological tissue of interest.

The interaction between gold nanoparticles and femtosecond laser irradiation has been shown to be effective in damaging malignant cells in two-dimensional cell cultures. Further studies with rodent models have also shown promising results; however, rodent physiology and genetics are known to differ substantially from that of humans, often failing to successfully predict the human response to treatment. For bridging the gap between two-dimensional cell cultures and animal models for plasmonic phototherapy, we use a natural hydrogel extracted from mouse sarcoma as a three dimensional scaffold for growing breast cancer epithelial cells in co-culture with healthy fibroblast cells. The malignant cells were specifically targeted using anti-EGFR-coated gold nanospheres, followed by washout of unbound particles and irradiation by amplified femtosecond pulses at off-resonance wavelength of 800 nm. Irradiated cell colonies seized to develop and grow; after approximately three days, time-lapse imaging revealed widespread death of both normal fibroblasts and malignant epithelial cells, leading to disintegration of all cell colonies. Pulse broadening experiments demonstrated similar cell death for pulses between 45 fs and 400 fs of equal energy, while pulses longer than 500 fs had no visible effect on the cells. The results suggest that cell damage is primarily photothermal, and that cells in three-dimensional cultures are more resistant to the effect of the laser pulses, requiring several irradiation sequences and exhibiting slow colony disintegration.

Ultrafast lasers are used to precisely ablate tissue below the surface. The maximum depth of ablation is ultimately limited by scattering and absorption by the tissue. As the depth of ablation is increased, higher laser powers are required to reach the ablation threshold at the laser focus, which leads to nonlinear self-focusing or surface damage. Here, we investigate self-focusing and the maximum depth of ablation in tissue experimentally and computationally. We find the maximum ablation depth in a model porcine tissue for a variety of focusing conditions and pulse widths by imaging ablation voids with third-harmonic generation imaging. The effect of self-focusing is measured by the shift in the focal plane of the ablation void and by the presence of self-focusing induced filaments. Computational models simulate laser pulse propagation and free-electron generation in tissue. Using our experimental data, we fit a nonlinear index to tissue. We then use the model to predict the role of self-focusing and the maximum ablation depth for a range of laser parameters.

One major barrier to advancing fundamental studies of biological cargoes for clinical use has been effective delivery into the cytoplasm. Available methods such as electroporation, viral techniques, and liposomal reagents come with respective strengths and weaknesses depending on the application needs. We present a laser-based cargo delivery platform that combines 11-ns laser pulses and structured flexible polymer substrates to create transient pores in the plasma membrane of cells. Cells are grown on the substrates, and pores are induced form on the cells in the regions excited with nanosecond laser pulses—thus, allowing treatment selectivity in a population. The medium surrounding the cell contains the delivery cargoes in solution, and cargoes diffuse into the cell before the transient pores are sealed. Polymer-based substrates are a promising material for laser-based delivery methods because they are low-cost, have flexible spatial movements, and have simple fabrication techniques. We deliver cargos of various sizes. We use fluorescence imaging and flow cytometry to quantify the delivery efficiency and viability in a reproducible manner. We obtain delivery efficiencies of up to 40% with viabilities of 60% for calcein green in adherent cells such as HeLa and Panc-1. We also deliver molecules of up to 40 kDas and siRNA. We use scanning electron microscopy to study cell adherence and substrate surface morphology. Our data shows that polymer-based substrates can deliver biological material directly into cells in a cost-effective manner.

Silver nanoparticles (Ag-NP) with Surface Enhanced Raman Scattering (SERS) activity were fabricated on a fused silica substrate by ultrafast femtosecond laser photoreduction of a silver salt solution. The SERS effectiveness of the Ag-NP increased with laser writing power and number of scans. SEM images show that the Ag-NP have a more uniform density distribution when using a multi-scan writing technique. A number of different laser parameters were compared, including scan speed, laser power, and number of scans. Overall, it was found that the most effective laser parameters were: 20 µms-1 scan speed, 10 mW laser power and 200 scans. The Ag-NP substrates have been used to detect single bacteria and hold promise to give fast, accurate and specific spectra according to the cell specimen present.

Ultra-short pulse laser texturing is a well-known one-step technique used to transform the surface properties of different materials in order to functionalize them for specific applications. According to the laser and process parameters, several features can be achieved, as surface coloring, blackening and super-hydrophobicity. In this work, an upscaling approach is considered for generation of surface structures and thermal effects, connected to the use of high-average power lasers are considered in relation to the influence of the laser pulse duration and repetition rate on the final surface morphology. Mirror-polished 316L steel samples were textured by an UPS laser source with pulse duration of about 450fs and running at 1030nm, at two different repetition rates, 250kHz and 1000kHz. Results show that two main sources of thermal effects are identified: (i) heat accumulation due to the use of high repetition rates and (ii) thermal diffusion effects linked to the intrinsic nature of the material. When employing high repetition rates, a lower cumulative energy is necessary to highlight the influence of the pulse duration on the surface morphology. Finally, the influence of pulse duration and wavelength on the wetting properties of the material surface are also investigated.

The use of metal nanostructures to produce colour has recently attracted a great deal of interest. This interest is motivated by colours that can last a long time and that can be rendered down to the diffraction limit, and by processes that avoid the use of inks, paints or pigments for environmental, health or other reasons. The central idea consists of forming metal nanostructures which exhibit plasmon resonances in the visible such that the spectrum of reflected light renders a desired colour. We describe a single-step laser-writing process that produces a full palette of colours on bulk metal objects. The colours are rendered through spectral subtraction of incident white light. Surface plasmons on networks of metal nanoparticles created by laser ablation play a central role in the colour rendition. The plasmonic nature of the colours are studied via large-scale finite-difference time-domain simulations based on the statistical analysis of the nanoparticle distribution. The process is demonstrated on Ag, Au, Cu and Al surfaces, and on minted Ag coins targeting the collectibles market. We also discuss the use of these coloured surfaces in plasmonic assisted photochemistry and their passivation for day-to-day use. Reactions on silver that are normally driven by UV light exposure are demonstrated to occur in the visible spectrum.

Several applications based on laser machining of transparent materials by nonlinear induced absorption of ultra short pulses are meanwhile well established. We apply in-situ diagnostics for the development auf new and improved processing techniques. The novel pump-probe system offers flexible pulse duration, burst options, beam shaping and repetition rates up to 2 MHz at an extended range of probe delay. This allows a deep inside into the spatial and temporal characteristics of nonlinear absorption and subsequent relaxation. By including effects of incubation and accumulation, mechanisms on multiple temporal and spatial scales can be addressed.

This is exemplified by results achieved for ablation, welding and modification cutting by elongated beam shapes. At a probe delay in the ns-range, pressure waves can be observed. Applying fluence near threshold, a remarkable influence of accumulation on the absorption becomes obvious even at repetition rates down to 10 kHz. Increasing the repetition rate results in thermal load on a zone by far extending the initial absorption region, as can be seen by pump-probe polarization microscopy. Pump-probe diagnostics support aberration correction for improved modification cutting by Bessel-like beams. The examples on processing results highlight the achievements enabled by thorough consideration of the plurality of relevant effects.

We study supercontinuum (SC) generation in large-mode-area (LMA) photonic crystal fibers with various core sizes and lengths, pumped by a picosecond Nd:YVO₄ laser. Micro-joule level SC pulse energy is achieved, and the spectrum extends beyond 1600 nm, corresponding to an effective Raman detection range over 3000 wavenumbers. A multiplex CARS setup based on the SC source is constructed, and we demonstrate CARS acquisition in air, and compare the signal obtained with different LMA fiber parameters.

In this century of continuous exponential growth of communications worldwide, traditional electrical interconnection is finding increasingly difficult to respond to the bandwidth pressure, and photonic interconnection will most likely be the future standard. Planar lightwave circuit (PLC) technology is capable of high-throughput fabrication of low loss waveguides, but is in general limited to its 2D geometry. On the other hand femtosecond direct writing (FDW) provides a solid tool for the fabrication of optical circuits with great flexibility, exploiting its truly 3D properties, but suffers from higher losses and lower throughput. By combining with PLC technology, FDW could aid in the bridging of different layers of optical circuits, exponentially decreasing their footprint. We report in this work the fabrication of such optical vias. The fabrication of vertical waveguides in fused silica, using a IR femtosecond fiber laser, with parameters optimised to induce the previously reported micro-explosions mechanism inside fused silica. By using a long working distance water immersion objective, we reduced spherical aberrations due to a better phase matching with the glass. A helix path was applied to create a cone of damaged material, leaving a stress-induced central waveguide, with propagation losses lower than 1 dB/mm. Finally, we analyse the possibility of tilting these waveguides and its effect on their optical properties. This feature adds to the flexibility of this method, that could for example accommodate input/output angles of common coupling strategies used with PLC technologies.

The investigation of the photo-inscription of waveguides in Barium Gallo-Germanate glass (BGG: BaO, GeO2, Ga2O3) is presented. This type of glass has been chosen because of its robustness, its chemical stability and its transmission throughout the whole visible region up to 5 µm. Irradiation with a focused femtosecond laser pulse train of different BGG samples leads to relatively high positive refractive index changes over a wide range of exposure conditions. Waveguides with a controllable diameter ranging from 4 to 35 µm and index change up to 10-2 were inscribed. A glass sample with custom molecular composition, adding a halogen component to remove hydroxyl ions and reduce the absorption band near 3 µm, was fabricated. Inscription of low-loss waveguides was performed, supporting only two transverse modes at the wavelength of 2.78 µm, and matching well with single-mode fluoro-zirconate fibres at this wavelength. An upper bound for the propagation losses of 0.5±0.1 dB/cm was determined along the waveguides, mainly due to absorption of hydroxyl ions in the glass, which can further be reduced by improving the purification process. The results presented show the great potential of the BGG glass family for the fabrication of core waveguides operating in the 2-5 µm spectral range and open a pathway towards the integration of mid-IR photonic devices based on BGG glasses.

For astronomy, the search of exo-planets and spectral analysis of galaxies and stars with ground based telescopes is an ongoing topic especially with the future planned telescopes with even larger mirror diameters. But for the ground based observation the atmosphere is a limiting factor. Besides of air fluctuations also spectral noise is influencing the observation. A forest of emission lines by OH relaxations that are orders of magnitudes stronger than the stars and galaxies appear in the night sky. These lines vary in intensity but are fixed in wavelength. Therefore, fiber Bragg gratings (FBG) are a perfect tool for the suppression of these emission lines. FBGs provide a high filter quality by filtering out magnitudes of intensity in a narrow wavelength window of below 0.5nm bandwidth. Because fibers are already widely used in telescopes to deliver light into spectrographs, the FBGs could be inscribed directly into the fibers. But for astronomy mostly multimode fibers are used where FBGs do not work as needed because of the different propagation constants of higher modes. The solution is the transition to single mode fibers. In terms of compactness and robustness a multicore fiber would be the optimal solution. But the homogeneous modification of a multicore fiber is a challenging task. We report on the ultrashort pulse laser inscription of FBGs into a multicore fiber consisting of 7 cores. Furthermore, investigations on the homogeneity of the inscribed modifications as well as the spectral properties are presented. I would like to participate in the Student Competition.

Direct laser writing in glasses using femtosecond lasers has been widely used and extensively studied during the last two decades. This technique provides a robust and efficient way to directly inscribe 3D photonic devices in the volume of bulk glasses. Following direct laser writing, a local refractive index change is induced, that is generally classified under three different types (Type I, II and III). Each type allows the fabrication of its own variety of embedded 3D photonic components. More specifically, type I refractive index change is usually preferred for the formation of photo-inscribed waveguides [1]. However, in silver containing glasses, direct laser writing induces a novel type of refractive index change, called type A [2]. It is based on the creation of fluorescent silver clusters distributed on the vicinity of the laser-glass interaction voxel [3] allowing for the inscription of a novel type of waveguides [2] exhibiting numerous interesting properties. In this paper, a comparative study between Type A and Type I waveguides in silver containing zinc phosphate glasses is presented. The morphology of waveguides, guided mode profile, refractive index profile and propagation losses as well as a thermal stability study are presented. Finally, this study shows the similar functionality of Type A waveguides compared to type I, thus exhibiting some significant advantages leading the way for promising applications based on type A waveguides’. 1. Davis, K.M., et al., Writing waveguides in glass with a femtosecond laser. Optics Letters, 1996. 21(21): p. 1729-1731. 2. Abou Khalil, Alain., et al., DLW of new type of waveguides in silver containing glasses. Scientific Reports, Submitted. 3. Bellec, M., et al., Beat the diffraction limit in 3D direct laser writing in photosensitive glass. Optics Express, 2009. 17(12): p. 10304-10318.

We have demonstrated the suppression of ablation rate on a silicon surface irradiated by a double-pulse beam with two color laser in time delays of Δt = -900 - 900 ps. The double pulse beam consists of 810nm with 40fs pulse and 405nm with > 40fs pulse. The fundamental-pulse fluence F₈₁₀ is kept below ablation threshold (F_{th, 810nm} = 0.190 J/cm² ) while the second harmonic pulse fluence F₄₀₅ are kept above the ablation threshold (F_{th, 405nm} = 0.050 J/cm² ). We find that ablation rate of silicon is drastically decreased at delay times of 600ps.

Nano-texturing of surface by self-organised ablation ripples as well as modifications of internal volume of materials, transparent at the wavelength of laser irradiation, is gaining interest due to simplicity of direct laser writing/printing. With ultra-short laser pulses (τ_p < 1 ps) a wider range of structuring morphologies is accessible, namely, sub-wavelength ripples. The surface wave formed on the plasma-dielectric (air or substrate) explains difference of the formed pattern. These corresponding front- and back-side (in respect to the incoming laser beam) modes of laser structuring accounts for the ripple formation inside transparent materials, where a skin-layer plasma is formed. Emerging applications of nano-textured surfaces for bio-medical field are discussed.

By modification of transparent glasses and crystals with ultrafast laser radiation and subsequent wet-chemical etching (here named SLE = selective laser-induced etching), precise 3D structures have been produced, especially in quartz glass (fused silica), for more than a decade. By the combination of a high precision three-axis system to move the glass sample and a fast 3D beam steering system to move the laser focus, the SLE process is now suitable to produce more complex structures in a shorter time. We have programmed a printer driver for commercial CAD software and flexible machine software enabling the automated production of complex 3D glass parts with the LightFab 3D Printer. New examples of 3D precision glass parts e.g. for lab-on-a-chip applications (cell-sorting microfluidics), electronics (glass via and connectors), semiconductor (quartz chucks), optics and precision mechanics are presented. The SLE process is very scalable for high throughput since a faster writing speed results in higher selectivity and thus larger precision of the resulting structures. Thus SLE is a process which is suitable for mass production of 3D structures in glasses. Some examples of rapidly produced structures using our high speed beam deflection modules are demonstrated, which are the basis of our special machines enabling mass-production. Therefore, 3D printing of glasses is not only a niche technology for prototypes anymore.

Optical fibers are ubiquitous and inexpensive substrates commonly used in telecom, and more recently as a platform for innovative concepts such ‘lab-on-a-fiber’ ones, where multiple functionalities are integrated in the fiber substrate. One of the challenges for machining fibers is to overcome the substrate curvature, and to achieve high accuracy throughout the volume. Common techniques include the use of index-matching fluids and special fiber holding devices. Here, we discuss the machining of optical fibers combined with chemical etching using a specific tooling configuration, mimicking the principal of a lathe, numerically controlled down to micron precision. An analysis of the beam propagating through the fiber is used to compensate for optical aberrations, inherent to such geometry. Further, we also show the combination of this process with a CO2-laser morphing technique to achieve high accuracy shapes with optical quality surfaces.

By using a dual-chirped optical parametric amplification (DC-OPA) scheme, we demonstrate high-energy infrared (IR) pulses with TW-scale peak power in the wavelength region of 1 ∼ 3.5 μm. In the central wavelengths between 1.2 ∼ 1.8 μm, we obtained over 100 mJ pulse energy. DC-OPA, which is an energy scalable method for an OPA process, can allow us to use a joule-class Ti:sapphire laser system for pumping an OPA. To the best of our knowledge, our DC-OPA laser is the first 100-mJ-class IR source with pulse duration of shorter than 100 fs. Additionally, to show the ability of our DC-OPA laser system, we demonstrate an energy-scaling strategy of high-order harmonic driven by a loosely focused 1.5 μm pulse. Using a 4-cm Ne gas cell with a 3.5-m laser focusing length, soft x-ray harmonics beyond 200 eV are clearly enhanced by a phase-matching effect.

We report on TRUMPF´s ultrafast laser systems equipped with industrialized hollow core fiber laser light cables. Beam guidance in general by means of optical fibers, e.g. for multi kilowatt cw laser systems, has become an integral part of laser-based material processing. One advantage of fiber delivery, among others, is the mechanical separation between laser and processing head. An equally important benefit is given by the fact that the fiber end acts as an opto-mechanical fix-point close to successive optical elements in the processing head. Components like lenses, diffractive optical elements etc. can thus be designed towards higher efficiency which results in better material processing. These aspects gain increasing significance when the laser system operates in fundamental mode which is usually the case for ultrafast lasers. Through the last years beam guidance of ultrafast laser pulses by means of hollow core fiber technology established very rapidly. The combination of TRUMPF´s long-term stable ultrafast laser sources, passive fiber coupling, connector and packaging forms a flexible and powerful system for laser based material processing well suited for an industrial environment. In this article we demonstrate common material processing applications with ultrafast lasers realized with TRUMPF´s hollow core fiber delivery. The experimental results are contrasted and evaluated against conventional free space propagation in order to illustrate the performance of flexible ultrafast beam delivery.

Conference Presentation for "Femtosecond laser inscribed 5D optical memories"

Femtosecond laser exposure of fused silica in the non-ablative regime can lead to localized modifications of the material structure. In particular, over the last two decades, it has been demonstrated that one can tune the chemical, mechanical and optical properties of dielectrics by tightly focusing a femtosecond laser in their volume. In this work, we focus our attention on the thermo- mechanical properties of the fused silica. In particular, we demonstrate that one can tune the thermal expansion coefficient of the glass by using different exposure conditions and specific exposure patterns. Specifically, the thermomechanical properties of the homogenous, so-called, Regime I exposure, and the nanogratings formation ( Regime II) are studied by measuring the out-of-deflections of a bimorph structure using digital holographic microscopy, over a temperature range of the 0 – 100 degrees Celsius. The thermomechanical response depends not only on the type of structural change, but also on the induced stress in the pristine material as shown by others. The latter allow us to alter the thermal strain locally by using different type of writing strategies, in order to prestress selectively the material. This study is the first step to control the thermal expansion of transparent material using ultrafast laser, which is in particular interesting to near zero-thermal expansion of opto-mechanical devices.

The processing of transparent materials by ultrashort pulses has opened diverse promising and fast-growing application areas such as the cutting of glasses for consumer electronics. One of the major benefits is the precise energy deposition, which may result in local weakening of the glass and hence defines a preferential direction for the separation path.

Due to the vast variety of possible uses for different displays, research in this field is needed for more complex shapes and glasses of various thicknesses. Bessel-Gaussian beams with their elongated, thin focus profile and self-healing nature are an excellent fit, even for glasses up to several millimeters. Additional development to more complex beam profiles allows precise tailoring with respect to the mandatory specifications of the cutting process such as process speed or the realization of inner contours. One concept for the latter is the use of tilted Bessel-Gaussian beams to achieve both high quality and easy separation. Further approaches include the usage of higher-order Bessel beams or modified Gauss-Bessel beams. We employ digital holographic techniques to create the various profiles with the desired absorption distribution.

Traditional microscopes fail to characterize these sensible changes in the interaction region, since they are limited to visualize permanent changes (ex situ) of the glass structure only. We take advantage of pump-probe microscopy to receive concise recordings of the extinction mechanisms of the beam-material-interaction. With both, high temporal and spatial resolution of in-situ diagnostics we gain access to the entire process window which enables us to develop optimized processing parameters for high-quality glass cuttings.

We propose a cascade optical system for multifocusing ultrashort pulse beams. In this system, diffractive and refractive subsystems that are optically coupled in cascade correct chromatic aberrations, a phase plate compensates for angular dispersions, and material dispersions are removed by pre-chirping the input pulse. Achromaticity of the system is essential for simultaneous compensation of spatio-temporal pulse distortions. We designed a system by applying the aberration correction conditions derived from an ABCD-matrix analysis. The designed system was evaluated with 20-fs pulses by characterizing the transmitted pulses in beam width and pulse duration to verify the proposed distortion compensation scheme. This technology enables high-throughput ultrafast laser processing.

Recent advances in the manufacture of synthetic diamond are creating new opportunities for diamond as a material for advanced technology. Laser writing with femtosecond pulses enables 3D fabrication of a variety of components inside diamond for a range of applications. Focusing at high numerical aperture inside the diamond, with adaptive optics used for aberration correction, non-linear absorption leads to a perturbation of the diamond structure on a scale less than a micrometre, without any damage to the surrounding material or surface. Working in different fabrication regimes, it is possible to generate in the same system electrically conductive wires, optical waveguides and coherent colour centres. In this talk, we present our new results on structural characterisation of the laser modifications within diamond. These include the extraction of a cross-section from a laser written wire using a focused ion beam, which is subsequently thinned and analysed by transmission electron microscopy (TEM). This reveals the internal structure of the laser written features, crucially showing that there is no bulk conversion of the diamond and sp2 bonded carbon is only formed within small 100-nm scale clusters. The sp2 clusters are accompanied by micro-cracks in the principal diamond cleavage plane which mediate the generated stress.

To achieve a variety of experimental conditions, the OMEGA EP laser provides kilojoule-level pulses over a pulse-width range of 0.6 to 100 ps. Precise knowledge of the pulse width is important for laser system safety and the interpretation of experimental results. This paper describes the development and implementation of a single-shot, ultrashort-pulse measurement diagnostic, which provides an accurate characterization of the output pulse shape. We present a brief overview of the measurement algorithm; discuss design considerations necessary for implementation in a complex, userfacility environment; and review the results of the diagnostic commissioning shots, which demonstrated excellent agreement with predictions.

We implemented a "multi-grid" scheme in frequency-resolved optical gating’s (FROG’s) generalized projections algorithm to boost pulse-retrieval speed for complex pulses. The multi-grid algorithm uses a set of coarser arrays, created from the original fine array, to provide an initial guess for an efficient retrieval from the much larger fine trace. Multi-grid is most needed by pulses with complex temporal profiles, which are best measured by cross-correlation FROG (XFROG) techniques. Applying multi-grid to XFROG, we reduced the retrieval time for complex pulses with TBP_rms of 40 to 90 from their XFROG traces by factors of 7-10 for pulses.

The shape of manufactured microtubes is one of the most important properties in their numerous emerging applications areas, like drug delivery, microfluidics, and cell biology. However, making non-cylindrical microtubes with 3D features in a reproducible and single-step fashion, and meanwhile, with the ability of remote control has remained challenging. In this study, we demonstrate the controlled synthesis of highly curved 3D microtubes by two-photon polymerization with single exposure of structured optical vortices, which is generated by phase modulation with a liquid crystal spatial light modulator (SLM). We exploit the tight focusing property of the optical vortices along the light path to create 3D microtubes. By modulating the topological charge and symmetry of the optical vortices, the size and geometry of fabricated microtubes can be well controlled. Finally, we combine these two ideas with the use of magnetic nanoparticles doped resist to fabricate 3D microtubes with elaborate features and remote controllability. Precise rotation and motion of the microtubes are realized by external magnetic field. With the fabricated functional mocrotubes, elaborate capture, delivery, and realease of microparticles are demonstrated. The technology we introduce is simple, stable and achieves a high production rate to make a wide variety of functional 3D microtubes, which have broad applications in cargo transportation, drug delivery, biosensing, microfluidics, and targeted cell therapy.

Single-shot ablation of GaAs samples by a collinear femtosecond-nanosecond (fs-ns) dual-pulse is investigated. Significantly enhanced material removal is achieved by optimally combining a single 8 ns pulse at 1064 nm and a single 50 fs pulse at 800 nm in time. The resulting ablation craters are examined for inter-pulse delays ranging from -50 ns (ns first) to +1 μs (fs first) as well as very long delays of ±30 s. Crater profilometry is conducted with white light interferometry and optical microscopy to determine the volume of ablated material and identify surface features that reveal information about the physical mechanism of material removal during fs-ns dual-pulse ablation.

We consider a propagation of laser pulse in a semiconductor under the conditions of an occurrence of optical bistability, which appears due to a nonlinear absorption of the semiconductor. As a result, the domains of high concentration of free charged particles (electrons and ionized donors) occur if an intensity of the incident optical pulse is greater than certain intensity. As it is well-known, that an optical beam must undergo a diffraction on (or reflection from) the domains boundaries. Usually, the beam diffraction along a coordinate of the optical pulse propagation does not take into account by using the slowly varying envelope approximation for the laser pulse interaction with optical bistable element. Therefore, a reflection of the beam from the domains with abrupt boundary does not take into account under computer simulation of the laser pulse propagation. However, the optical beams, reflected from nonhomogeneities caused by the domains of high concentration of free-charged particles, can essentially influence on a formation of switching waves in a semiconductor. We illustrate this statement by computer simulation results provided on the base of nonlinear Schrödinger equation and a set of PDEs, which describe an evolution of the semiconductor characteristics (concentrations of free-charged particles and potential of an electric field strength), and taking into account the longitudinal and transverse diffraction effects.

We present a mathematical approach to appreciate that short pulse characterization requires recognizing inseparability of the measurements of the amplitude envelope-correlation and spectral measurements and then use a suitable iterative approach to derive the real characteristics. We will use a standard Michelson interferometer, as usual, to introduce the autocorrelation function of a pulse containing single and multiple frequencies. In the process, we also underscore that detectors play the key role in generating measurable Superposition Effects (SE), recognized as fringes after the detectors carry out the square modulus operation. Simple mathematical summation of amplitude factors, the Superposition Principle (SP), is not directly observable. We underscore this by mentioning that we present EM waves as classical and detectors as quantum mechanical. This semi-classical approach has been established by Lamb and Jaynes, which is indirectly supported by Glauber’s comment, “A photon is what a detector detects”. The semi-classical approach helps us separate the phenomenological difference between the absorbed detected energy by a detector (SE) from the energy supplied by the simultaneously present multiple wave amplitudes (SP). As in atomic and molecular physics, we use the detector’s dipolar stimulation as the product of its linear dipolar polarizability multiplied by all the EM fields stimulating it simultaneously. The analysis also demonstrates that for a pulse containing multiple frequencies, the two-beam autocorrelation function becomes a product of the traditional amplitude correlation factor and a frequency-comb correlation factor. Hence, the spectral interpretation of a short pulse and two-beam autocorrelation are inseparable. Therefore, the detailed characterization would require iterative computational approach by guessing the most plausible functional forms. This deeper understanding can be applied to rapid re-calibration of pulsed lasers that need to be maintained at single mode but has the tendency to move to multimode behavior. If the newly measured autocorrelation function differs from the original amplitude correlation factor, then one should check for the spectral characteristics first, before assuming that only the pulse shape has changed.

The advances of the picosecond and femtosecond laser installations utilization for radiation hardness evaluation of semiconductor electronics for space applications are presented. The modern “local laser irradiation” method for single event effects testing of semiconductor devices, not requiring calibration by ions is described. The essence of the local approach is in irradiating the sample sensitive volume, positioned at some distance from the focus plane, where the beam becomes divergent. Due to such optical effects as single or multiple reflections, scattering, diffraction, reflections from air-SiO₂ boundary, interference, absorption in n⁺/p⁺/poly-Si layers and reflection from bottom side of substrate, the laser light partially penetrates into the sensitive volume, screened by the presence of multilayer metallization,n⁺/p⁺ nearsurface layers, regions of polysilicon in the passivation layer, etc. Assuming single-photon absorption the relationship between the laser pulse energy and the excess charge actually generated in irradiated sensitive volume is obtained by the measurement of the electrical response, thus taking into account the non-uniform optical losses and avoiding additional calibration by ions. Some results, obtained using both the front-side and the backside local irradiation of devices, are presented. Comparison with the results obtained using focused laser radiation with subsequent calibration by ions showed that the laser-only measurements, based on local irradiation, give the correct estimates of radiation hardness parameters. It is shown that the use of backside local irradiation method is the most suitable for laser single event effects tests.

This work compares the effects of ablation on GaAs, Al, and Ti samples exposed to two different regimes: a focused 800nm, 14.13mJ pulse of 55fs duration from a Ti: Sapphire laser with an intensity of 2×10¹⁶ W cm^-2 and a focused 1064nm, 14.61mJ pulse of 10ns duration from a Nd: YAG laser with an intensity of 2×10¹⁰ W cm^-2. The craters are examined using optical microscopy, white light interferometry, and scanning electron microscopy. Among the effects examined in this paper are the conduction of energy throughout the material, formation of nanodroplets outside of the crater, nanopits in the center of the crater, and the effects of phase explosion inside the crater.

Microfluidics technology which deals with small liquid samples and reagents within micro-scale channels has been widely applied in various aspects of biological, chemical, and life-scientific research. For fabricating microfluidic devices, a silicon-based polymer, PDMS (Polydimethylsiloxane), is widely used in soft lithography, but it has several drawbacks for microfluidic applications. Glass has many advantages over PDMS due to its excellent optical, chemical, and mechanical properties. However, difficulties in fabrication of glass microfluidic devices that requires multiple skilled steps such as MEMS technology taking several hours to days, impedes broad application of glass based devices. Here, we demonstrate a rapid and optical prototyping of a glass microfluidic device by using femtosecond laser assisted selective etching (LASE) and femtosecond laser welding. A microfluidic droplet generator was fabricated as a demonstration of a microfluidic device using our proposed prototyping. The fabrication time of a single glass chip containing few centimeter long and complex-shaped microfluidic channels was drastically reduced in an hour with the proposed laser based rapid and simple glass micromachining and hermetic packaging technique.