This PDF file contains the front matter associated with SPIE Proceedings Volume 9355, including the Title Page, Copyright information, Table of Contents, Authors, and Conference Committee listing.

Since their introduction in 1986, stents have transformed the treatment of coronary heart disease and other arterial occlusions. Today, millions of stents are implanted worldwide each year to treat various vascular and endovascular diseases caused by the narrowing or blockage of blood vessels. Nearly all commercially available stents are made from metals. Theses stents remain in the vessels permanently after implantation and are prone to cause serious medical complications in many cases. One potential solution to avoid such complications is to use stents made out of bioabsorbable materials. Bio-absorbable stents dissolves in the human body after serving their purpose. However, machining of bio-absorbable material is a challenging task. In this paper the influence of the laser process parameters on the efficiency and quality of the machining of bio-absorbable materials using Spirit® femtosecond laser system from Spectra-Physics is presented.

We investigate the effect of optical and thermal properties in laser-induced periodic surface structures (LIPSS) formation on a poly-L-lactic acid (PLLA), a biodegradable polymer. Surface properties of biomaterials are known to be one of the key factors in tissue engineering. Methods to process biomaterial surfaces have been studied widely to enhance cell adhesive and anisotropic properties. LIPSS formation has advantages in a dry processing which is able to process complex-shaped surfaces without using a toxic chemical component. LIPSS, however, was difficult to be formed on PLLA due to its thermal and optical properties compared to other polymers. To obtain new perspectives in effect of these properties above, LIPSS formation dependences on wavelength, pulse duration and repetition rate have been studied. At 800 nm of incident wavelength, high-spatial frequency LIPSS (HSFL) was formed after applying 10000 femtosecond pulses at 1.0 J/cm² in laser fluence. At 400 nm of the wavelength, HSFL was formed at fluences higher than 0.20 J/cm² with more than 3000 pulses. Since LIPSS was less formed with lower repetition rate, certain heat accumulation may be required for LIPSS formation. With the pulse duration of 2.0 ps, higher laser fluence as well as number of pulses compared to the case of 120 fs was necessary. This indicates that multiphoton absorption process is essential for LIPSS formation. Study on biodegradation modification was also performed.

Zeolite catalysis has been exploited by the petrochemical industry since the 1940’s for catalytic cracking reactions of long chain hydrocarbons. The selectivity of zeolites strongly depends on a pore size, which is controlled by the chosen structure-directing agent (SDA) and by the SDA decomposition/removal process. Although zeolites are composed of micron-sized crystals, studies of zeolite materials typically focus on bulk (i.e., ensemble) measurements to elucidate structure-function information or to optimize catalysts and/or process parameters. To examine these phenomena on the microscale, non-linear optical microscopy is used to provide real-time imaging of chemical reactions in zeolites at temperatures exceeding 400^°C. The template decomposition mechanism is studied, as elucidation of the mechanism is critical to understanding the relationship between the decomposition chemistry and the nanoscale features of the zeolite (topology, Si/Al ratio, added dopants). Forward stimulated Raman scattering (SRS), forward coherent anti-Stokes Raman scattering (CARS) and epi two-photon fluorescence (TPF) modalities are acquired simultaneously providing video-rate structural and chemical information. A high-temperature cell with gas inlet system is used for the study of reactions under various temperatures and gas environments. Examining the decomposition process with single-particle resolution enables access to ensemble-level and spatially-resolved behavior. Parallel experiments on bulk zeolite powders are conducted to enable comparison of ensemble and single-particle behavior during template decomposition. Our multi-technique approach has high potential for gaining insight into the link between nanoscale structure and catalytic activity and selectivity of zeolitic materials.

Using a femtosecond pulsed laser system (pulse width = 100fs, repetition rate = 1kHz, λ = 800nm), ablation threshold studies of freshly culled bovine and ovine cortical bone samples were identified using the diameter regression technique. Using the D2 technique, the ablation threshold was found to lie within a range of 0.83 - 0.96 Jcm⁻² and 0.89 - 0.95 Jcm⁻² for ovine and bovine cortical bone respectively indicating that laser ablation of bone is irrespective of target species.

The relationship between cortical bone tissue removal and the number of applied pulses was explored. By altering the laser spot translation rate, we varied the number of pulses at each point along scribed linear cuts. Optical Coherence Tomography (OCT) and PDMS casting indicates that cut depth is linearly dependent on the number of pulses applied to the tissue, irrespective of donor species. For single pulse ablation of ovine and bovine cortical bone, we determined that the ablation rates were 0.41 - 0.75 μm per pulse and 0.28 - 0.90 μm per pulse when pulses of fluences in the range 0.52 - 2.63 Jcm⁻² were applied to ovine and bovine cortical bone tissue, respectively. Structural analysis of the ablation features using environmental scanning electron microscopy and optical microscopy were utilized to assess the ablation features and identify signs of damage to surrounding tissue. We observed no structural indications of thermal shockwave cracking, molten debris deposition or charring of the tissue whilst leaving hydroxyapatite crystal structure intact.

The interaction of cell-adhered nanostructures with laser light has attracted much interest within the biomedical field. Molecular delivery using a variety of plasmonic nanostructures, such as structured surfaces, nanoparticles and particle clusters, is currently evolving from its proof-of-concept into a routine method. Here, gold represents the material of choice, as it provides unique optical properties, different surface modifications as well as biocompatibility. In addition, new materials (e.g. polypyrrole) provide interesting alternatives.

Applying this approach, a variety of molecules, such as fluorescent dyes, proteins, antisense structures, and DNA, has been transfected in order to manipulate the cellular functions in different experimental settings. Antisense structures, for example, allow the efficient down regulation of the gene activity of a target, providing insights into the gene’s function. The delivery of proteins, as executing molecules in the cell, can exhibit an immediate effect on the cell behavior, allowing a minute observation of the intracellular kinetics.

Direct cell manipulation can be achieved with this approach as well. Increasing the nanoparticle concentration and/or the radiant exposure, effective cell destruction is induced. Using targeted nanoparticles (e.g. by antibody conjugation) in combination with spatially selective laser irradiation permits well-directed cell manipulation even in mixed cultures and potentially in tissues. Furthermore, excited gold nanoparticles can directly trigger cellular reactions, which can possibly be utilized for cell stimulation. The manifold possibilities of nanostructure assisted laser manipulation are still in development.

Single nerve cell’s mechanical response is an important issue for understanding function of nerve system, though, the response has been rarely clear. One of the factors is difficulty to stimulate the single cells by quantitative and controllable mechanical stress with subcellular spatial selectivity. As such mechanical stimulator, our group has focused on shock and stress waves generated by focusing the femtosecond laser under a microscope. When those waves impact on the biological cell, they act as an impulsive force. Although the impulsive force is available as a mechanical manipulator of the single cells, it was not confirmed that it could stimulate the nerve cells. Here we investigated the issue using neuro2a cells extending their neurite as an experimental model of nerve cell. Our results indicated that the impulsive force could be available as the stimulator to cause the mechanical response of the neuro2a cell.

Laser-based transfection techniques have gained significant interest during the last decade. Either single cell manipulation by focusing on the cell membrane or high-throughput can be realized with laser transfection. The latter is for example provided by gold nanoparticle mediated laser transfection. It is based on the heating of gold nanoparticles through laser irradiation, which permeabilizes the membrane. This technique satisfies most prerequisites of a reliable transfection technique, like efficiency and minimal cell impact. In order to bring it closer to routine usage, we investigated new particle configurations for gold nanoparticle mediated laser transfection. Our setup employs a 532 nm and 850 ps laser system. We immobilized gold particles on cell culture surfaces or modified silica particles with a gold particle surface coverage. Furthermore, first experiments achieving cell perforation with an organic nanoparticle based on polypyrrole were conducted. These three options achieved comparable efficiencies to the incubation of cells with free gold nanoparticles. With regard to the underlying mechanisms of perforation, we performed fluorescence microscopy based imaging of the cell state combined with holographic imaging directly after perforation. First results indicated a power dependent ion (calcium) and volume exchange with the extracellular medium in the first two minutes after perforation. In conclusion, our results can pave the way to a safer and more efficient way of high-throughput laser transfection with gold nanoparticles.

Optical stretching is a powerful technique for the mechanical phenotyping of single suspended cells that exploits cell deformability as an inherent functional marker. Dual-beam optical trapping and stretching of cells is a recognized tool to investigate their viscoelastic properties. The optical stretcher has the ability to deform cells through optical forces without physical contact or bead attachment. In addition, it is the only method that can be combined with microfluidic delivery, allowing for the serial, high-throughput measurement of the optical deformability and the selective sorting of single specific cells. Femtosecond laser micromachining can fabricate in the same chip both the microfluidic channel and the optical waveguides, producing a monolithic device with a very precise alignment between the components and very low sensitivity to external perturbations. Femtosecond laser irradiation in a fused silica chip followed by chemical etching in hydrofluoric acid has been used to fabricate the microfluidic channels where the cells move by pressure-driven flow. With the same femtosecond laser source two optical waveguides, orthogonal to the microfluidic channel and opposing each other, have been written inside the chip. Here we present an optimized writing process that provides improved wall roughness of the micro-channels allowing high-quality imaging. In addition, we will show results on cell sorting on the basis of mechanical properties in the same device: the different deformability exhibited by metastatic and tumorigenic cells has been exploited to obtain a metastasis-cells enriched sample. The enrichment is verified by exploiting, after cells collection, fluorescence microscopy.

The duration of energetic ultrashort pulses is usually limited by the available gain bandwidth of ultrashort amplifiers used to amplify nJ or pJ level seed to hundreds of μμJ or even several mJ. In the case of Ytterbium-doped fiber amplifiers, the available bandwidth is of the order of 40 nm, typically limiting the pulse duration of high-energy fiber chirped-pulse amplifiers to durations above 300 fs. In the case of solid-state amplifier based on Yb:YAG crystals, the host matrix order restricts the amplification bandwidth even more leading to pulses in the low picosecond range. Both architecture would greatly benefit from pulse durations well-below what is allowed by their respective gain bandwidth e.g. sub-100 fs for fiber amplifier and sub-300 fs for solid-state Yb:YAG amplifier. In this contribution, we report on the post-compression of two high energy industrial ultrashort fiber and thin-disk amplifiers using an innovative and efficient hollow core fiber structure, namely the hypocycloid-core Kagome fiber. This fiber exhibits remarkably low propagation losses due to the unique inhibited guidance mechanism that minimize that amount of light propagating in the silica cladding surrounding the hollow core. Spectral broadening is realized in a short piece of Kagome fiber filled with air at 1 atmosphere pressure. For both amplifiers, we were able to demonstrate more than 200 μJ of energy per pulse with duration <100 fs in the case of the fiber amplifier and <300 fs in the case of the thin disk amplifier. Limitations and further energy scaling will also be discussed.

We demonstrate a simple single-shot device, called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram (STRIPED FISH), for completely characterizing the intensity and phase of an arbitrary ultrashort pulse in space and time (x,y,t). Improvements are made on the measurable bandwidth, aberrations eliminations, and the intensity uniformity of the multiple holograms in our device. To demonstrate the capability, we perform single-camera-frame measurements of spatiotemporally complex subpicosecond crossed and chirped double pulses from a Ti:Sapphire oscillator. To display the resulting four-dimensional intensity-and-phase data, we generate intuitive movies of the measured pulses based on our newly-developed method.

Frequency combs are a massively parallel source of extremely accurate optical frequencies. Frequency combs generally operate at the visible or near-infrared wavelengths, but fundamental molecular vibrations occur at midinfrared wavelengths. We demonstrate an optically-referenced, broadband midinfrared frequency comb based on a doublyresonant optical parametric oscillator (OPO). By tuning the wavelength of the reference laser, the comb line frequencies are tuned as well. By scanning the reference wavelength, any frequency can be accessed, not just the frequencies of the base comb. Combined with our comb-resolving Fourier transform spectrometer, we can measure 200 wavenumber wide broadband absorption spectra with 200 kHz linewidth comb teeth.

Our OPO is pumped by an amplified Tm fiber frequency comb, with phase-locked carrier envelope offset frequency, and repetition rate fixed by phase-locking a frequency comb line to a narrow linewidth diode laser at a telecom channel. The frequency comb is referenced to GPS by long-term stabilization of the repetition rate to a selected value using the temperature of the reference laser as the control. The resulting pump comb is about 3W of 100 fs pulses at 418 MHz repetition rate at 1950 nm. Part of the comb is used for supercontinuum generation for frequency stabilization, and the rest pumps an orientation-patterned gallium arsenide (OP-GaAs) crystal in a doubly-resonant optical parametric oscillator cavity, yielding collinear signal and idler beams from about 3 to 5.5 μm.

We verify comb scanning by resolving the 200 MHz wide absorption lines of the entire fundamental CO vibrational manifold at 11 Torr pressure.

We demonstrate an ultrahigh-rate imaging system applied to very high speed microscopic flows. Chirp processing of ultrafast laser pulses in optical fiber is employed to create pseudorandom spectral patterns at a rate of one unique pattern per pulse. These spectral patterns then serve as structured illumination of the object flows inside a 1D spatial disperser before digitization at a rate of one sample per optical pulse with a fast single pixel photodetector. Diffraction-limited microscopic imaging of flows up to 31.2 m/s is achieved at up to 19.8 and 39.6 Gigapixel/sec rates from a 720 MHz acquisition rate.

Single-pulse coherently controlled nonlinear Raman spectroscopy is the simplest method among the coherent anti-Stokes Raman spectroscopy systems. In recent research, it has been proven that notch-shaped femtosecond pulse laser can be used to collect the coherent anti-Stokes Raman signals. In this study, we applied a fiber Bragg grating to the notch filtering component on the femtosecond pulse lasers. The experiment was performed incorporating a titanium sapphire femtosecond pulse laser source with a 100 mm length of 780-HP fiber which is inscribed 30 mm of Bragg grating. The fiber Bragg grating has 785 nm Bragg wavelength with 0.9 nm bandwidth. We proved that if the pulse lasers have above a certain level of positive group delay dispersion, it is sufficient to propagate in the fiber Bragg grating without any spectral distortion. After passing through the fiber Bragg grating, the pulse laser is reflected on the chirped mirror for 40 times to make the transform-limited pulse. Finally, the pulse time duration was 37 fs, average power was 50mW, and showed an adequate notch shape. Furthermore, the simulation of third order polarization signal is performed using MATLAB tools and the simulation result shows that spectral characteristic and time duration of the pulse is sufficient to use as an excitation source for single-pulse coherent anti-Stokes Raman spectroscopy. In conclusion, the proposed method is more simple and cost-effective than the methods of previous research which use grating pairs and resonant photonic crystal slab.

In this paper the results of micromachining of polycarbonate polymer foils and SUS304 stainless steel thin sheets are reported, performed by an industrial femtosecond laser operated at 1030 nm and 515 nm (SHG) wavelength. For a typical Galvoscanner setup the ablation scribing was investigated at a spotsize of 20 μm which is typical for contemporary feature size used for medical stents. At this value a maximum peak intensity of 6.4*10¹³ W/cm^² can be reached, which enables significant nonlinear absorption in the polymer.

Laser pulse overlap was varied to optimize overlap values for best edge quality and for best ablation rate.

From the results some guidelines for complete cutting of thin sheets were derived. For an acceptable edge quality a maximum ablation rate of 2.6 mm^³/min was demonstrated for stainless steel thin sheets, whereas up to 9,4 mm³/min have been reached for polycarbonate.

For SUS304 the use of the SHG does not increase ablation rate or edge quality, whereas for polycarbonate the cutting quality is better, but at a smaller ablation rate.

The formation of randomly distributed or periodic holes with a depth of several μm can be observed during the ablation of silicon with ultrafast lasers. In order to investigate the conditions for these hole formations, Si wafers with a thickness of 525 μm were ablated using a 380-fs laser at a wavelength of 520 nm. The surface was scanned parallel and perpendicular to the polarization of the laser beam with different fluences and numbers of scans. The ablated surfaces were analyzed by scanning electron microscopy. Their roughness was measured using confocal microscopy. At a fluences of 1.4 J/cm², laser-induced periodic surface structures (LIPSS) orientate parallel to the polarization and periodic holes appear in the furrows independently of the polarization. At 4.3 J/cm², LIPPS can be suppressed and the hole formation is reduced, if the polarization is perpendicular to the scan direction. The surface roughness reduces by a factor of 2. At 14.1 J/cm², the formation of LIPPS is suppressed independently of the polarization, but the surface roughness increases again due to the increasing amount and size of melt ejections. The analysis of the surface suggests that random stacking of melt ejections creates bumps and holes. The depth of the holes increases with the number of scans. In this way, first random and then—with increasing number of scans—periodic holes appear. This effect can be enhanced by creating LIPPS.

The local inscription of strong birefringence by ultrashort laser pulses facilitates the fabrication of manifold photonic devices, such as data storage devices. One intriguing feature of these nanograting-based data units is to delete and rewrite new nanograting voxels by changing the laser polarization orientation during inscription. However, up to now no comprehensive picture of this complex physical process exists. Thus we performed optical retardance measurements as well as microscopic analyses, such as small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) to address this issue.

Our results reveal that only few laser pulses already lead to an erasure of nanometric pores which is mapped by the total (X-ray) scattering volume as well as by the strong reduction of the initial form birefringence. Simultaneously, new nanostructures form which arrange in individual grating planes with ongoing irradiation. However, since the rewrite process is no ideal mechanism some of the old sheets remain, which perturb the quality of the new nanograting. When rewriting multiple times the glass becomes even more porous due to repetitive annealing and quenching. This promotes the formation of new inhomogeneities and in turn leads to an increase in optical retardance.

Graphitic wires embedded beneath the surface of single crystal diamond are demonstrated. Through a combination of ultrashort (femtosecond) pulsed fabrication, high numerical aperture focusing and adaptive optics, wires are created with sub micrometre dimensions that can follow any three dimensional path within the diamond. The increased level of focal control available through the use of adaptive optics appears particularly important in the generation of high quality wires, with measured conductivities over an order of magnitude greater than previous laser-induced graphitic wires in diamond. Applications for the embedded wires are discussed.

We report on the first direct measurements of the laser induced temperature distribution after the absorption of multiple ultrashort laser pulses at high repetition rates in borosilicate glass. To this end, we developed an in-situ micro Raman setup to determine the temperature dependent ratio between Stokes and Anti-Stokes scattering. The results indicate a critical influence of the pulse energy on the induced temperature.

In borosilicate glass, the maximal temperature directly after the excitation (pulse energy of 1100 nJ, repetition rate of 1 MHz, wavelength of 1044 nm, pulse duration of 600 fs, 2000 pulses per laser spot) is more than 5000 K and rapidly cools down within several hundreds of ns.

Microfluidic lenses are a powerful tool for many lab on a chip applications ranging from sensing to detection and also to imaging purpose, with the great advantage to increase the degree of integration and compactness of these micro devices. In this work we present the realization of such a compact microfluidic lens with reconfigurable optical properties. The technique used to realize the device we present is femtosecond laser micromachining followed by chemical etching, which allows to easily fabricate 3D microfluidic devices with an arbitrary shape. Thanks to that it has been possible to easily fabricate different lens made up by cylindrical microchannel in fused silica glasses filled with liquids with a proper refractive index. The optical properties of these devices are tested and shown to be in a good agreement with the theoretical model previously implemented. Furthermore we have also optimized the design of these microlenses in order to reduce the effects of spherical aberrations in the focal region, thus allowing us to obtain a set of different acylindrical microfluidic lenses, whose validation is also reported. In this work the lens adaptability can be achieved by replacing the liquid inside the microchannel, so that we can easily tune the feature of the focused beam. Thus increasing the possible range of applications of these micro optical elements, as an example we report on the validation of the device as a fast integrated optofluidic shutter.

Near-infrared (NIR) dyes absorb and emit light within the range from 700 to 900 nm have several benefits in biological studies for one- and/or two-photon excitation for deeper penetration of tissues. These molecules undergo vibrational and rotational motion in the relaxation of the excited electronic states, Due to the less than ideal anisotropy behavior of NIR dyes stemming from the fluorophores elongated structures and short fluorescence lifetime in picosecond range, no significant efforts have been made to recognize the theory of these dyes in time-resolved polarization dynamics. In this study, the depolarization of the fluorescence due to emission from rotational deactivation in solution will be measured with the excitation of a linearly polarized femtosecond laser pulse and a streak camera. The theory, experiment and application of the ultrafast fluorescence polarization dynamics and anisotropy are illustrated with examples of two of the most important medical based dyes. One is NIR dye, namely Indocyanine Green (ICG) and is compared with Fluorescein which is in visible range with much longer lifetime. A set of first-order linear differential equations was developed to model fluorescence polarization dynamics of NIR dye in picosecond range. Using this model, the important parameters of ultrafast polarization spectroscopy were identified: risetime, initial time, fluorescence lifetime, and rotation times.

The permanent refractive index change induced by ultrashort laser pulses in zinc phosphate glasses has been investigated both at the surface and in bulk. At the sample surface, irradiations have been performed by using loosely focused single fs-laser pulses at different energies. Optical microscopy images of the irradiations illustrate an interferometric pattern in form of concentric Newton rings due to the laser induced multilayer system (unmodified glass, thin laser-modified layer, air). This experimental reflectivity modulation along with simulations based on Abeles theory for multilayer optical systems allows retrieving laser-induced refractive index changes on the order of Δns= -10^-3. In bulk, fs-laser written waveguides have been generated by translating the sample with respect to a tightly focused laser beam. The so-produced waveguides have been characterized by studying the optical near field of the TEM₀₀ guided mode at 660 nm and using white light microscopy. The optical changes linked to the inscribed waveguides have been characterized by measuring the far field output profiles yielding values of approximately Δn_b= +3·10^-4. The laser-modified optical properties in bulk and at the surface will be linked to the glass structural changes as well as discussed in terms of the role of the incubation effects for multi-pulse processing.

The installations for laser testing of microelectronic elements (first of all - integrated circuits) of devices for space applications for hardness to local radiation effects from heavy charged particles are presented. The possibility of a focused pulsed laser radiation application to the study of local radiation effects, caused by single heavy charged particles, is explained. The fundamentals of an approach to the construction of test sets, based on the picosecond and femtosecond lasers and systems for focusing their radiation, are considered. The main technical requirements for the basic modules of sets for laser testing (laser wavelength and pulse duration and repetition rate, spatial beam parameters and minimal spot size, speed of object movement and so on) are substantiated. All worked out sets have a full-featured software for the operational management of all modules of the laser test facility, including the positioning of the object, to provide feedback from the measurement results of the reaction of the object on the laser excitation. The parameters of developed laser hardware and software systems and their foreign counterparts are compared. Further improvement directions for laser testing tools are briefly outlined. The discussion is also presented of described hardware technical and operational characteristics, allowing to use it for a variety of scientific research studies, requiring selective (with submicron spatial resolution) object excitation by ultrashort laser pulses and recording responses to this effect with the exact timing of the moment of excitation, as well as to perform a variety of high precision technological operations.