This PDF file contains the front matter associated with SPIE Proceedings Volume 7925, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

A microcavity biosensor monitors optical resonances in micro- and nanostrucrtures for label-free detection of molecules and their interactions. I will give an introduction to the field of microcavity biosensing and present an overview on the current state-of-the art. I will emphasize recent applications of optical microcavities for nanoparticle detection, trapping and manipulation, and I will highlight different modalities for ultra-sensitve label-free biosensing.

We have found that ultrafast laser microbeam inducing bubble(s) can lead to condensation of molecules in solution. The laser microbeam was generated by coupling a near infrared mode-locked femtosecond (fs) laser beam onto an inverted fluorescence microscope and focusing it with a 100X objective. Fluorescence imaging revealed that collapse of cavitation micro-bubbles created high-concentration regions of dye molecules in the aqueous solution. Further, twophoton excitation of the molecules under the ultrafast laser microbeam showed significant increase in fluorescence intensity as a function of laser exposure time without micro-bubble formation. This may be attributed to nano-bubble formation and or conformational change in the molecules under intense laser intensity at the focused spot to significantly enhance the molar absorptivity (extinction coefficient) or fluorescence excitation cross-section. High-concentration regions of the dye molecules are found to be retained for a longer period of time and therefore provide an opportunity for collection of these condensed molecules using microcapilary and/or for further analysis.

Quantum dots have been used in a wide variety of biomedical applications. A key advantage of these particles is that their optical properties depend predictably on size, which enables tuning of the emission wavelength. Recently, it was found that CdSe/ZnS quantum dots lose their ability to photoluminescence after exposure to gamma radiation (J. Phys. Chem. C., 113: 2580-2585 (2009). A method for readout of the loss of quantum dot photoluminescence during exposure to radiation could enable a multitude of real-time dosimetry applications. Here, we report on a method to image photoluminescence from quantum dots from a distance and under ambient lighting conditions. The approach was to construct and test a time-gated imaging system that incorporated pulsed illumination. The system was constructed from a pulsed green laser (Nd:YAG, 20 pulses/s, 5 ns pulse duration, ~5 mJ/pulse), a time-gated camera (LaVision Picostar, 2 ns gate width), and optical components to enable coaxial illumination and imaging. Using the system to image samples of equivalent concentration to the previous end-point work, quantum dot photoluminescence was measureable under ambient room lighting at a distance of 25 cm from the sample with a signal to background of 7.5:1. Continuous exposure of samples to pulsed laser produced no measureable loss of photoluminescence over a time period of one hour. With improvements to the light collection optics the range of the system is expected to increase to several metres, which will enable imaging of samples during exposure to a gamma radiation source.

Analysis of trapped microscopic objects using fluorescence and Raman spectroscopy is gaining considerable interest. We report on the development of single fiber femto second optical tweezers and its use in two-photon fluorescence (TPF) excitation of trapped fluorescent particles. Trapping of the floating objects led to stable fluorescence emission intensity over a long period of time, suitable for spectroscopic measurements. Trapping depth of few cm was achieved inside colloidal sample with TPF from the trapped particle being visible to the naked eye. Furthermore, the fiber optic trapping was so stable that the trapped particle could be moved in 3D even by holding the fiber in hand and slow maneuvering of the same. Owing to the propagation distance of the Bessel-like beam emerging from the axicon-fiber tip, a relatively longer streak of fluorescence was observed along the microsphere length. The cone angle of axicon was engineered so as to provide better trapping stability and high axial confinement of TPF. The theoretical simulation of fiber optical microbeam profiles emerging from the axicon tip and trapping force estimations was found to be in good agreement with the experimentally observed stiffness and TPF patterns. Apart from miniaturization capability into lab-on- a-chip micro-fluidic devices, the proposed non-invasive micro axicon tipped optical fiber can be used in multifunctional mode for in-depth trapping, rotation, sorting and ablation as well as for two-photon fluorescence excitation of motile sample which will revolutionize biophysics and research in material science.

This paper aims at presenting a review of work at the Laser Thermal Laboratory on the microscopic laser modification of biological materials using ultrafast laser pulses. We have devised a new method for fabricating high aspect ratio patterns of varying height by using two-photon polymerization process in order to study contact guidance and directed growth of biological cells. Studies using NIH-3T3 and MDCK cells indicate that cell morphology on fiber scaffolds is influenced by the pattern of actin microfilament bundles. Cells experienced different strength of contact guidance depending on the ridge height. Cell morphology and motility was investigated on micronscale anisotropic cross patterns and parallel line patterns having different aspect ratios. A significant effect on cell alignment and directionality of migration was observed. Cell morphology and motility were influenced by the aspect ratio of the cross pattern, the grid size, and the ridge height. Cell contractility was examined microscopically in order to measure contractile forces generated by individual cells on self-standing fiber scaffolds.

We report on generation of blue light exploiting high-order mode propagation in a microstructured fiber pumped by a Ti:Sapphire close to the zero-dispersion wavelength of the first high-order mode. An new interesting regime was observed with axial offset pump. With 230 mW of incident pump power we generated over 3 mW in the 450-510 nm window achieving 50 μW/nm power density. In a final round of measurements we were able to show generation of a peak at 350 nm. This complex regime has still to be fully investigated but we believe an optimized fiber design will allow to efficiently extend the operation of Ti:Sapphire laser to UV/blue wavelength region.

We propose a holographic spatiotemporal lens to improve spatial resolution of two-photon excitation spot as a new focusing technique of femtosecond laser pulse. Femtosecond laser pulses dispersed by a diffraction grating are irradiated to a chirped diffractive lens displayed on a spatial light modulator. The chirped diffractive lens has a spatially chirp of focal length for a design for its corresponding wavelength. The shortest pulse was experimentally obtained only at the focal plane. The pulse duration was also supported with a computer simulation.

Femtosecond laser induced cell membrane poration has proven to be an attractive alternative to the classical methods of drug and gene delivery. It is a selective, sterile, non-contact technique that offers a highly localized operation, low toxicity and consistent performance. However, its broader application still requires the development of robust, high-throughput and user-friendly systems. We present a system capable of unassisted enhanced targeted optoinjection and phototransfection of adherent mammalian cells with a femtosecond laser. We demonstrate the advantages of a dynamic diffractive optical element, namely a spatial light modulator (SLM) for precise three dimensional positioning of the beam. It enables the implementation of a "point-and-shoot" system in which using the software interface a user simply points at the cell and a predefined sequence of precisely positioned doses can be applied. We show that irradiation in three axial positions alleviates the problem of exact beam positioning on the cell membrane and doubles the number of viably optoinjected cells when compared with a single dose. The presented system enables untargeted raster scan irradiation which provides transfection of adherent cells at the throughput of 1 cell per second.

The gold nanoparticle (AuNP) mediated ultrashort laser cell membrane perforation has been proven as an efficient delivery method to bring membrane impermeable molecules into the cytoplasm. Nevertheless, the underlying mechanisms have not been fully determined yet. Different effects may occur when irradiating a AuNP with ultrashort laser pulses and finally enable the molecule to transfer. Depending on the parameters (pulse length, laser fluence and wavelength, particle size and shape, etc.) light absorption or an enhanced near field scattering can lead to perforation of the cell membrane when the particle is in close vicinity. Here we present our experimental results to clarify the perforation initiating mechanisms. The generation of cavitation and gas bubbles due to the laser induced effects were observed via time resolved imaging. Additionally, pump-probe experiments for bubble detection was performed. Furthermore, in our patch clamp studies a depolarization of the membrane potential and the current through the membrane of AuNP loaded cell during laser treatment was detected. This indicates an exchange of extra- and intra cellular ions trough the perforated cell membrane for some milliseconds. Additionally investigations by ESEM imaging were applied to study the interaction of cells and AuNP after co incubation. The images show an attachment of AuNP at the cell membrane after several hours of incubation. Moreover, images of irradiated and AuNP loaded cells were taken to visualize the laser induced effects.

This paper presents a complete partial differential equation based model to describe the interaction of an ultrafast laser with a plasmonic nanostructure in water. Apart from heating the structure itself, it is shown that this interaction also leads to the generation of a plasma in the water medium and to the production of a strong pressure wave and a nanobubble in the vicinity of the structure. Plasma collisions and relaxation are shown to be the main source of mechanical stress in the medium and the dominant factor for the pressure wave and bubble creation. An all-optical technique able to detect plasmonic enhanced bubble formation and pressure wave generation is also presented.

In this paper, we present the results of in vitro gene transfer by plasmonic enhanced optoporation of human melanoma cells. The fs-laser based optoporation is a gentle and efficient method for transfection. An optimum perforation rate with efficient dye or DNA uptake and high viability of the cells (~90%) was found for different types of nanostructures, spherical and rod shaped. The technique offers a very high selectivity and the low damage induced to the cell leads to a high transfection efficiency. The cell selectivity of this technique on the one hand is realized by using bioconjugated nanostructures, that couple selectively to a special cell type, and on the other hand, the spatial selectivity is due to the fact that only irradiated cells are perforated. In many biological applications a virus free and efficient transfection method is needed, especially in terms of its use in vivo. In cancer cells, the aggressiveness of the cells is shown in the migration and invasion velocity. The laser based and nanostructure enhanced transfection of cells offers the possibility to directly compare the treated and untreated cells. The treatment for migration and invasion assays can be performed by laser-scraping and laser transfection, resulting in a fully non-contact and therefore sterile method where the shape and the size of the scrape is well defined and reproducible. The laser based scrape test therefore offers less uncertainty due to scrape variations, high transfection efficiency, as well as direct comparison of treated and control cells in the same dish.

Manipulation of cells requires the delivery of membrane-impermeable substances like genetic materials or proteins into the cytoplasm. Thus delivery of molecules over the cell membrane barrier is one of the key technologies in molecular biology. Many techniques concerning especially the delivery foreign DNA have been developed. Notwithstanding there still is a range of applications where these standard techniques fail to raise the desired results due to low efficiencies, high toxicity or other safety issues. Especially the transfection of sensitive cell types like primary and stem cells can be problematic. Here we present an alternative, laser based technique to perforate the cell membrane and thus allowing efficient delivery of extra cellular molecules: Gold nanoparticles (GNP) are brought into close contact with the cell, were the laser-GNP interaction leads to membrane perforation. This allows the utilisation of a weakly focused laser beam leading to fast scanning of the sample and thus to a high throughput. To investigate the GNP-laser interaction in more detail we have compared membrane perforation obtained by different laser pulse lengths. From our results we assume strong light absorption for ps laser pulses and relatively small particles as the initiating perforation mechanism, whereas an enhanced near field scattering occurs at 200 nm GNP when using fs laser pulses. SEM and ESEM imaging were applied to give a deeper insight in the GNP-cell interaction and the effects of laser radiation on the GNP. Additionally dextran- FITC derivatives of varying sizes were used to investigate the impact of molecule size on delivery efficiency.

The femtosecond laser direct-write technique was used to create a 2x2 single-mode waveguide coupler in Yb-doped borosilicate glass. Initial modelling demonstrates that a reversible change in splitting ratio at 800 nm of more than 20% is possible (i.e. 50:50 to 30:70) if a shift in refractive index of the order of 1×10^-4 can be induced. Such a shift is expected to be achieved through resonant optical excitation at 976 nm of the ytterbium ions, which increases the refractive index through heating and the direct pumping of a saturable optical absorption.

A 1030 nm pulsed femtosecond laser has been use to induce modifications in silver containing glass namely femto-photo luminescent glass (FPL) and Photo-thermo refractive glass (PTR). The 5W 10Mhz laser is focused at a depth of 200 μm in the glass using a 0,52 NA objective. The output polarization of the laser is TM. The tailoring of the number of pulses, pulse energy and repetition rate is achieve by acousto-optic filtering. The interaction resulted in the creation of stable pipe-shaped silver clusters forming bellow refraction-limit 3D structures. Those nano-structures exhibit non-linear properties such as SHG and THG as well as fluorescence. Due to multiphoton absorption, free electrons are created in the central part of the beam, enabling the reduction of Ag⁺ silver ions into Ag⁰ and subsequently Ag_m^X+. The cumulated thermal effect of the pulses weakens the glass matrix allowing the diffusion of the Ag_m^X+. The ion concentration gradient creates a buried electric field enabling non-linear properties. Influences of polarization, dose and fluence on the nonlinear properties are investigated. Our explanation of the causes of SHG and THG are validated by the accordance between the theory and the measurement. Comparisons between theoretic model and our results showing accordance in the limits of out 2D model are demonstrated using different incoming polarizations.

Three-dimensional optical recording by laser-induced fluorescent silver clusters is demonstrated in glass. The fluorescence properties of these stable clusters can be altered, depending on the glass recording exposure conditions. A "Blu-ray"-like drive enables readout of the information inside the glass without cross-talk and photobleaching. This original recording medium can provide an answer to the societal problem of long-term high-density data storage.

Femtosecond laser filaments leave plasma strings at their trail as they propagate through any transparent medium including glasses and polymers. This initial plasma string and the energy deposited from the electrons to the lattice play a fundamental role in the creation of permanent structural modifications in these media.

We report on measurements of the breaking stress of glass substrates welded with ultrashort laser pulses. Femtosecond laser pulses at repetition rates in the MHz range are focused at the interface between two substrates, resulting in multiphoton absorption and heat accumulation from successive pulses. This leads to local melting and subsequent resolidification results in the formation of strong bonds at the interface. The achievable breaking stress of this flexible and local bonding process is discussed in detail in dependence of the processing parameters.

Ultrashort pulses lasers are tools of choice for functionalizing the bulk of transparent materials. In particular, direct photoinscription of simple photonic functions have been demonstrated. Those elementary functions rely on the local refractive index change induced when focusing an ultrashort pulse in the volume of a transparent material. The range of possibilities offered by direct photoinscription is still under investigation. To help understanding, optimizing and assessing the full potential of this method, we developed a time-resolved phase contrast microscopy setup. The imaginary part (absorption) and the real part of the laser-induced complex refractive index can be visualized in the irradiated region. The setup is based on a commercially available phase contrast microscope extended into a pump-probe scheme. The originality of our approach is that the illumination is performed by using a pulsed laser source (i.e. a probe beam). Speckle-related issues are solved by employing adequate sets of diffusers. This laser-microscopy technique has a spatial resolution of 650 nm, and the impulse response is about 300 fs. The laser-induced refractive index changes can be tracked up to milliseconds after the energy deposition. The excitation beam (the pump) is focused with a microscope objective (numerical aperture of 0.45) into the bulk of an a-SiO₂ sample. The pump beam can be temporally shaped with a SLM-based pulse shaping unit. This additional degree of flexibility allows for observing different interaction regimes. For instance, bulk material processing with femtosecond and picosecond duration pulses will be studied.

We demonstrate a compact and robust picosecond fiber amplifier system that produces >25-μJ pulse energy and average powers exceeding 25W while maintaining a narrow spectral bandwidth. This simple and compact CPA-free fiber amplifier system is well suited for micro-machining applications as well as for scientific applications that require narrow optical spectra as e.g. CARS spectroscopy.

This paper demonstrates that disk-laser technology introduces advantages that increase efficiency and allows for high productivity in micro-processing in both the nanosecond (ns) and picosecond (ps) regimes. Some technical advantages of disk technology include not requiring good pump beam quality or special wavelengths for pumping of the disk, high optical efficiencies, no thermal lensing effects and a possible scaling of output power without an increase of pump beam quality. With cavity-dumping, the pulse duration of the disk laser can be specified between 30 and hundreds of nanoseconds, but is independent of frequency, thus maintaining process stability. TRUMPF uses this technology in the 750 watts average power laser TruMicro 7050. High intensity, along with fluency, is important for high ablation rates in thinfilm removal. Thus, these ns lasers show high removal rates, above 60 cm²/s, in thin-film solar cell production. In addition, recent results in paint-stripping of aerospace material prove the green credentials and high processing rates inherent with this technology as it can potentially replace toxic chemical processes. The ps disk technology meanwhile is used in, for example, scribing of solar cells, wafer dicing and drilling injector nozzles, as the pulse duration is short enough to minimize heat input in the laser-matter interaction. In the TruMicro Series 5000, the multi-pass regenerative amplifier stage combines high optical-optical efficiencies together with excellent output beam quality for pulse durations of only 6 ps and high pulse energies of up to 0.25 mJ.

Spatial characterization of high harmonics (HH) and XUV coherent radiation is of paramount importance, along with its temporal characterization. For many applications it will be necessary to accurately measure the beam properties, just as it is important to know the beam characteristics for many laser experiments. For example, high harmonics and attosecond pulses are being proposed as a front-end for the next generation X-ray free electron lasers. This oscillator-amplifier-like arrangement will require well characterized high harmonic sources. On the other hand, the electromagnetic radiation carries the combined signature of underlying quantum physical processes at the molecular level and of the cooperative phase matching. For example, accurate reconstruction of the high harmonic spatial wavefront, along with its temporal profile, gives us a complete range of tools to apply to the fundamental quantum properties and dynamics associated with high harmonic generation. We present a new concept of frequency resolved wavefront characterization that is particularly suitable for characterizing XUV radiation. In keeping with tradition in the area we give it an acronym - SWORD (Spectral Wavefront Optical Reconstruction by Diffraction). Our approach is based on an analysis of the diffraction pattern of a slit situated in front of a flat-field spectrometer. As the slit is scanned, the spectrally resolved diffraction pattern is recorded. Analyzing the measured diffractogram, we can reconstruct the wavefront. The technique can be easily extended beyond the XUV spectral region. When combined with temporal characterization techniques all information about the beam can be measured.

Simulating coherent control with femtosecond pulses on a polyatomic molecule with anharmonic splitting was demonstrated. The simulation mimicked pulse shaping of a Spatial Light Modulator (SLM) and the interaction was described with the Von Neumann equation. A transform limited pulse with a fluence of 600 J/m² produced 18% of the population in an arbitrarily chosen upper vibrational state, n =2. Phase only and amplitude only shaped pulse produced optimum values of 60% and 40% respectively, of the population in the vibrational state, n=2, after interaction with the ultra short pulse. The combination of phase and amplitude shaping produced the best results, 80% of the population was in the targeted vibrational state, n=2, after interaction. These simulations were carried out with all the population initially in the ground vibrational level. It was found that even at room temperatures (300 Kelvin) that the population in the selected level is comparable with the case where all population is initially in the ground vibrational state. With a 10% noise added to the amplitude and phase masks, selective excitation of the targeted vibrational state is still possible.

Micro-molding can be used for the cost-effective fabrication of elements such as active or passive components in MEMS devices, hydrophobic surfaces, cell-growth scaffolds or optical components such micro-lens arrays and gratings. This method is also particularly interesting for examining high-aspect ratio laser-machined structures fabricated in glass material. Thanks to this technique, surfaces not accessible with common imaging techniques can be observed on their molded negative structure with very high fidelity. As an illustration, we issue the use of the PDMS molding technique to analyze the quality of high aspect ratio holes and channels structures. Furthermore, we show preliminary results on the molding of a novel type of complex structures formed in glass using temporal and spatial beam shaping.

We present apodised Bragg waveguides inscribed in fused silica using a high repetition rate fs laser system. By varying the modulation with a pulse picker, the mean refractive index over the grating length could be kept constant, while the grating strength is varied. Thus, Bragg waveguides with zero crossing Gaussian modulation profile could be demonstrated. The side-lobes were suppressed by about 10 dB compared to a uniform grating.

Recently, it was demonstrated that femtosecond lasers pulses with energies below the ablation threshold locally enhance the etching rate of fused silica: regions that are exposed to the laser beam are etched faster. This remarkable property has been used for fabricating a variety of micro-structures like fluidic channels, tunnels or more complex devices, like mechanical flexures. The physical effect causing the etching-rate local enhancement is still debated and various hypotheses have been proposed among which localized densification models seem to prevail. In that context, we recently demonstrated that the amount of deposited energy plays a very important role. It was found that for laser repetition rates where no cumulative effects are observed, there exists an optimal amount of energy deposited to achieve the fastest etching rate. These observations suggest that the stress introduced during laser exposure plays an important role in the processing of fused silica with low energy ultrafast pulses. In this paper, we investigate the stress distributions in various laser patterns and how this stress distribution can account for various effects observed during processing such as a local etching enhancement, the occurrence of cracks in dense patterns made of multiple lines and finally, the presence of stress-induced birefringence.

Fundamental results of ablation processes of metals with ultrashort laser pulses in the far threshold fluence regime are shown and discussed. Time-resolved measurements of the plasma transmission exhibit two distinctive minima. The minima occurring within the first nanoseconds can be attributed to electrons and sublimated material emitted from the target surface, whereas the subsequent minimum after several 10 ns is due to particles and droplets after a thermal boiling process. Industrial applications of ultrashort pulsed laser micro machining in the Bosch Group are also shown with the production of exhaust gas sensors and common rail diesel systems. Since 2007, ultrashort laser pulses are used at the BOSCH plant in Bamberg for producing lambda-probes, which are made of a special ceramic layer system and can measure the exhaust gas properties faster and more accurately. This enables further reduction of emissions by optimized combustion control. Since 2009, BOSCH uses ultrashort pulsed lasers for micro-structuring the injector of common rail diesel systems. A drainage groove allows a tight system even at increased pressures up to 2000 bar. Diesel injection is thus even more reliable, powerful and environment-friendly.

Molybdenum films on a glass substrate are ablated from the glass side by picosecond laser pulses at fluences below 1 J/cm², without damage. Thin films of chromium, titanium and platinum with thicknesses between 200 nm and 1 μm were examined to investigate the underlying ablation mechanisms. For molybdenum an influence of the intermediate buffer layer was observed. Ablation from the glass side clearly has higher ablation efficiency and a better structural quality in contrast to metal side patterning. A model will be presented, in which the ablation characteristics are connected with the mechanical ductility of the metal.

This paper reports on the colorizing of the stainless steel surface by controlling the irradiation conditions of a single-beam femtosecond laser. We change the color of the stainless steel surface by femtosecond laser induced periodic self-organized nanogratings or microgratings on the sample surface. Colorizing of metal surface by periodic microholes, produced by femtosecond laser, is achieved for the first time. The laser modified stainless steel surfaces show different colors under different incident or azimuthal angles of the incident light, which changes in color indicate the dependence of the metal color on the angles (incident and azimuthal) of the incident light. We report, for the first time, the changes of metal color due to the change of the azimuthal angles of the incident light. Furthermore, the changes in the color of the laser modified metal surfaces are mainly due to the excitation of surface plasmon polaritons (SPPs) on the metal surface. The resonant angle of SPPs is different for different wavelength of light. As a result, under different incident or azimuthal angles different wavelength of light is trapped on the surface depending on the resonance for that particular wavelength; light of other wavelengths react naturally and contributes for the color change of the stainless steel surfaces. Finally, we discovered that the nanostructures produced inside the self-organized nanogratings and microholes play important roles for the propagation of the SPPs in parallel with the nanogratings and mcroholes, which nanostructures are responsible for a complex SPPs excitation on the sample surface.

Yield stress of 80 μm thick glass wafer chip diced with fs-laser μ-processing was investigated with varying the repetition rate of laser pulse and scanning speed under constant number of shot. By using constant laser fluence, the yield stress is almost invariant at lower repetition rate less than 20 kHz, but abruptly drops to the half of initial yield stress. Based on the effect of the ambient gas on the transition point of yield stress changes, we propose an empirical relation between the yield stress and cumulative stress caused by temperature increment with changing the laser repetition rate.

We report on ablation experiments of sputter deposited thin film systems of NiCr and Al₂O₃ for the fabrication of strain sensors. To ensure proper functionality of the electrical circuits, the metal film has to be selectively removed while damage in the Al₂O₃ films has to be avoided. Damage thresholds of the Al₂O₃ layer are investigated and damage mechanisms are discussed. Damage thresholds decrease with increasing number of scans until reaching a constant value. The processing window defined as the ratio of Al₂O₃ damage threshold and NiCr ablation threshold increases with increasing film thickness and number of scans.

In applications ranging from noncontact microsurgery to semiconductor blind hole drilling, precise depth control of laser processing is essential. Even a priori characterization cannot compensate for material heterogeneity and stochasticity inherent to the material modification process. We image along the machining beam axis at high speeds (up to 312 kHz) to provide real-time feedback, even in high aspect ratio holes. The in situ metrology is based on broadband coherent imaging (similar to the medical imaging modality optical coherence tomography) and is practical for a wide-range of light sources and machining processes (e.g., thermal cutting using a quasi-continuous wave fiber laser, or nonlinear ablation achieved with ultrafast pulses). Coherent imaging has high dynamic range (> 60 dB) and strongly rejects incoherent signals allowing weak features to be observed in the presence of intense machining light and bright plasmas. High axial resolution (~5 μm) is achieved with broadband imaging light but center wavelength can be chosen appropriate to the application. Infrared (wavelength: 1320±35 nm) allow simultaneous monitoring of both surface and subsurface interfaces in nonabsorbing materials like tissue and semiconductors. Silicon based detector technology can be used with near infrared imaging light (804 ± 30 nm) enabling high speed acquisition (>300 kHz) or low cost implementation (total imaging system <10k$). Machining with an appropriate broadband ultrafast laser allows machining and imaging to be done with the same light source. Ultrafast technology also enables nonlinear optical processing of the imaging light, opening the door to improved imaging modalities.

We report on the in-situ observation of the laser drilling process using ultrashort laser pulses. Our technique is based on transmission imaging of a silicon sample at 1060 nm. For drilling, we used a laser system that provides pulses with a duration of 8 ps at 1030 nm. This wavelength is below the band edge and silicon shows linear absorption. The beam is focused on the sample surface perpendicular to the transillumination. Therefore, the temporal evolution of the longitudinal silhouette of the hole can be visualized during the drilling progress. Our observations show a change of the drilling dynamics in the depth of the material. Effects like the decrease in ablation rate, the formation of bulges, deviations in drilling direction and finally a branching of the hole end occur due to the influence of the previously excavated capillary. That causes a perturbation of the beam by internal reflections and the interaction with ablation products as well as their additional abrasive effect. The dependence of hole depth and shape on the process parameters, especially fluence and pulse energy, is studied. The maximum achievable hole depth in deep drilling is chiefly determined by the pulse energy but largely independent of fluence.

Due to the steadily advancing miniaturization in all fields of technology nanostructuring becomes increasingly important. Whereas the classical lithographic nanostructuring suffers from both high costs and low flexibility, for many applications in biomedicine and technology laser based nanostructuring approaches, where near-field effects allow a sub-diffraction limited laser focusing, are on the rise. In combination with ultrashort pulsed laser sources, that allow the utilization of non-linear multi-photon absorption effects, a flexible, low-cost laser based nanostructuring with sub-wavelength resolution becomes possible. Among various near-field nanostructuring approaches the microsphere based techniques, which use small microbead particles of the size of the wavelength for a sub-diffraction limited focusing of pulsed laser radiation, are the most promising. Compared to the tip or aperture based techniques this approach is very robust and can be applied both for a large-scale production of periodic arrays of nanostructures and in combination with optical trapping also for a direct-write. Size and shape of the features produced by microsphere near-field nanostructuring strongly depend on the respective processing parameters. In this contribution a basic study of the influence of processing parameters on the microsphere near-field nanostructuring with nano-, pico- and femtosecond laser pulses will be presented. The experimental and numerical results with dielectric and metal nanoparticles on semiconductor and dielectric substrates show the influence of particle size and material, substrate material, pulse duration, laser fluence, number of contributing laser pulses and polarization on the structuring process.

The formation of laser induced periodic surface structures (LIPSS) is to a large extent of self-organizing nature and in its early stages essentially influenced by optical scattering. The evolution of related mechanisms, however, has still to be studied in detail and strongly depends on materials and laser parameters. Excitation with highly intense ultrashort pulses leads to the creation of nanoripple structures with periods far below the fundamental wavelength because of opening multiphoton excitation channels. Because of the drastically reduced spatial scale of such laser induced periodic nanostructures (LIPNS), a particular influence of scattering is expected in this special case. Here we report on first investigations of femtosecond-laser induced nanostructuring of sputtered titanium dioxide (TiO₂) layers in comparison to bulk material. The crucial role of the optical film quality for the morphology of the resulting LIPNS was worked out. Typical periods of nanoripples were found to be within the range of 80-180 nm for an excitation wavelength of 800 nm. Unlike our previously reported results on bulk TiO₂, LIPNS in thin films appeared preferentially at low pulse numbers (N=5-20). This observation was explained by a higher number of scattering centers caused by the thin film structure and interfaces. The basic assumptions are further supported by supplementary experiments with polished and unpolished surfaces of bulk TiO₂ single crystals.

We report an invisible two-dimensional (2D) barcode embedded into a synthetic fused silica by femtosecond laser processing using a computer-generated hologram (CGH) that generates a spatially extended femtosecond pulse beam in the depth direction. When we illuminate the irradiated 2D barcode pattern with a 254 nm ultraviolet (UV) light, a strong red photoluminescence (PL) is observed, and we can read it by using a complementary metal oxide semiconductor (CMOS) camera and image processing technology. This work provides a novel barcode fabrication method by femtosecond laser processing using a CGH and a barcode reading method by a red PL.

Using femtosecond laser processing with glass-hologram, fabrication of 1cm-long straight waveguide and X-coupler is reported in this paper. We design and fabricate 4-level glass-hologram which generates 1cm-long straight line intensity. We fabricate 1cm-long waveguides inside fused silica at one shot exposure with the glass-hologram. We investigate the waveguide performance of near field pattern and propagation loss at wavelength of 1550nm. The near field pattern is almost circular shape. The propagation loss at 1550nm is estimated to be < 1.0 dB/cm. As an example of an optical device consisting of straight waveguides, we fabricate X-coupler or 2x2 coupler using straight line waveguides, and observe the output power ratio depending on crossing angle.