This PDF file contains the front matter associated with SPIE Proceedings Volume 8247, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Transfection is the process of introducing DNA into cells so that the introduced DNA will function and produce proteins. This technique is useful to study the function of various DNA sequences and in the future may lead to gene therapy for curing genetic diseases. Currently, a number of techniques are available for both population and individual cells transfection. Although individual cells transfection is less commonly used than the population transfection, it has benefits because it allows controlled single cell analysis. In this paper, we present a new laser assisted transfection method for individual cells. In this technique, two lasers are used to perform the transfection procedure and third laser is used to detect the position of DNA coated nanoparticle which is inserted in the cell. This technique has relatively high transfection efficiency and good post-transfection cell viability.

Recent studies have shown that mechanical factors can direct stem cell fate in vitro, even in the absence of biochemical factors. Two-photon laser polymerization was applied here to fabricate ultra-precise 3D micro-scaffolds with different architectures and pore sizes able to structurally interact with cells at the single-cell scale. Our experiments have shown that randomly seeded mesenchymal stem cells systematically colonize the internal volumes of 3D scaffolds and proliferate, while showing a roundish morphology. Even if stem cell mechanobiology is a very complex field, this study shows how mechanical interactions studied in a 3D micro-architecture at a single cell scale may influence stem cells response.

In this paper we report imaged neuronal rat cells in a confocal laser scanning microscope by simultaneous generation of the three requested wavelengths obtained by a UV-extended supercontinuum source. This is to the best of our knowledge that such a measure was performed using a microstructured fiber pumped by a standard Ti:Sapphire laser. We observed efficient UV light generation when a novel pumping scheme was used. The pump wavelength is close to the zero-dispersion wavelength of the fiber first high-order mode and offset axial pumping is used. By tuning the pump wavelength and power level we were able to generate mW-power levels in the visible wavelength interval down and of about hundreds of microwatt in the UV wavelength interval down to 300 nm. The pump alignment was very simple and very stable. We believe that further optimization of pump wavelength, fiber length and fiber zero-dispersion wavelength could generate light well below 300 nm using a simple and stable set-up. To demonstrate the potentiality of this technique we imaged neuronal rat cells in a confocal laser scanning microscope by simultaneous generation of the three requested wavelengths.

In this contribution we report on a novel approach for pump and stokes pulse generation in extremely compact all-fiber systems using parametric frequency conversion (four-wave-mixing) in photonic-crystal fibers. Representing a completely alignment-free approach, the all-fiber ytterbium-based short-pulse laser system provides intrinsically synchronized tunable two-color picosecond pulses emitted from a single fiber end. The system was designed to address important CH-stretch vibrational resonances. Strong CARS signals are generated and proved by spectroscopic experiments, tuning the laser over the resonance of toluene at 3050cm^-1. Furthermore the whole laser setup with a footprint of only 30x30cm² is mounted on a home-built laser-scanning-microscope and CARS imaging capabilities are verified. The compact turn-key system represents a significant advance for CARS microscopy to enter real-world, in particular bio-medical, applications.

We demonstrate a novel low noise, tunable, high-peak-power, ultrafast laser system based on a SESAM-modelocked, solid-state Yb tungstate laser plus spectral broadening via a microstructured fiber followed by pulse compression. The spectral selection, tuning, and pulse compression are performed with a simple prism compressor. The spectral broadening and fiber parameters are chosen to insure low-noise operation of the tunable output. The long-term stable output pulses are tunable from 800 to 1200 nm, with a peak power up to 30 kW and pulse duration down to 26 fs. This system is attractive for variety of applications including ultrafast spectroscopy, multiphoton (TPE, SHG, THG, CARS) and multimodal microscopy, nanosurgery, nanostructuring, and optical coherence tomography (OCT). Such system is simpler, lower-cost, and much easier to use (fully turn-key) compared to a currently available solutions for near-infrared ultrashort pulses, typically a Ti:sapphire laser-pumped OPO.

High average power, high repetition rate femtosecond lasers with μJ pulse energies are increasingly used for bio-medical and material processing applications. With the introduction of femtosecond laser systems such as the High Q femtoREGEN^TM UC platform, micro-processing of solid targets with femtosecond laser pulses have obtained new perspectives for industrial applications. The unique advantage of material processing with sub-picosecond lasers is efficient, fast and localized energy deposition, which leads to high ablation efficiency and accuracy in nearly all kinds of solid materials. In this paper, we will show aspects of the design and performance of the femtoREGEN^TM UC industrial laser system and give an overview of actual applications.

We demonstrated a compact femtosecond laser producing 1mJ pulse energy and more than 30 W average power using the amplification of a broadband femtosecond oscillator in an Yb:YAG thin disk regenerative amplifier in a compact CPA configuration. The pulse duration slightly decreases with energy down to a value of 790 fs still keeping the amplified spectral width <3 nm and thus suitable for efficient second harmonic generation. This source answers to the need for high power, high energy and reliable femtosecond sources notably in the field of innovative precision micromachining and high repetition rate OPA/OPCPA pumping.

We demonstrate a simple device for measuring two independent ultrashort pulses, each of which can potentially be complex and can also have very different center wavelength, simultaneously in a single-shot. We call our device "double-blind" FROG and it is implemented using a polarization-gate geometry. In polarization-gate "double-blind" FROG, each pulse acts as a reference pulse for the measurement of the other and yields the intensity and phase of both pulses.

The fundamental importance of length measurement and traceability is clear. In July 2009, the national standard tool for measuring length in Japan changed from an iodine-stabilized helium-neon (He-Ne) laser to a femtosecond optical frequency comb (FOFC). Because of the great potential for a technological revolution in length measurement, FOFC based length measurement has attracted much attention from physicists and engineers. This paper is intended to give a description to the concept, the principle, and a demonstration of a new length measurement technique, called pulse repetition interval-based Excess Fraction (PRIEF) method, which was developed for an arbitrary and absolute length measurement that is directly linked to an FOFC. The basic idea of this new technique was inspired by the analogy between the wavelength of a monochromatic laser source and the pulse repetition interval of an FOFC. Just as a conventional Excess Fraction method can determine an arbitrary and absolute length of a gauge block based on the wavelength of a monochromatic laser source, the same Excess Fraction method can range an arbitrary and absolute length as a function of the pulse repetition interval of an FOFC. A demonstration of the proposed method is presented. A literature review of pulse laser based length measurement is also performed. From the result of the preliminary experiment and the literature review, it has been show the possibility that PRIEF method can be used for a high-accuracy distant evaluation.

Photonics is a powerful framework for testing in experiments quantum information ideas, which promise significant advantages in computation, cryptography, measurement and simulation tasks. Linear optics is in principle sufficient to achieve universal quantum computation, but stability requirements become severe when experiments have to be implemented with bulk components. Integrated photonic circuits, on the contrary, due to their compact monolithic structure, easily overcome stability and size limitations of bench-top setups. Anyway, for quantum information applications, they have been operated so far only with fixed polarization states of the photons. On the other hand, many important quantum information processes and sources of entangled photon states are based on the polarization degree of freedom. In our work we demonstrate femtosecond laser fabrication of novel integrated components which are able to support and manipulate polarization entangled photons. The low birefringence and the unique possibility of engineering three-dimensional circuit layouts, allow femtosecond laser written waveguides to be eminently suited for quantum optics applications. In fact, this technology enables to realize polarization insensitive circuits which have been employed for entangled Bell state filtration and implementation of discrete quantum walk of entangled photons. Polarization sensitive devices can also be fabricated, such as partially polarizing directional couplers, which have enabled on-chip integration of quantum logic gates reaching high fidelity operation.

In this paper we examine the birefringence of buried optical waveguides written with femtosecond lasers in bulk fused silica glass. We report two modes of low and high birefringence associated with strong form birefringence and the orientation of nanogratings that align perpendicular to the writing laser polarization. The birefringence and waveguide losses are characterized over various laser exposure conditions to facilitate the fabrication of low-loss and compact wave retarders and polarization beam splitters for integration into polarization controlled circuits. Zero-order quarter-wave and half-wave retarders together with polarization beam splitters are demonstrated, all operating at telecom wavelengths. Integration of such devices is targeted for application in photonic quantum circuits.

To gain insight into the processes mediating the cumulative action of subsequent laser pulses which gives rise to the formation of nanogratings, we performed double pulse experiments with femtosecond laser pulses with a delay time ranging from 0.5 ps to 1 ns. We determined the polarisation contrast intensity of the inscribed lines as a measure for the birefringent strength of the nanogratings. Our experiments show an enhanced nanograting formation for pulse separations below 500 ps. We attribute this to the presence of self trapped excitons serving as transient material memory enhancing the impact of the second pulse. In contrast, nanograting formation at pulse separation times up to several seconds is being mediated by dangling bond type defects as evidenced by spectrally resolved absorption measurements.

Ultrashort pulse lasers offer the possibility to structure the bulk of transparent materials on a microscale. As a result, the optical properties of the irradiated material are locally modified in a permanent fashion. Depending on the irradiation parameters, different types of laser-induced phase objects can be expected, from uniform voxels (that can exhibit higher or lower refractive index than the bulk) to self-organized nanoplanes. We study the physical mechanisms that lead to material restructuring, with a particular emphasis on events taking place on a sub picosecond to a microsecond timescale following laser excitation. Those timescales are particularly interesting as they correspond to the temporal distances between two consecutive laser pulses when performing multiple pulse irradiation: burst microprocessing usually involves picosecond separation times and high repetition rate systems operate in the MHz range. We employ a time-resolved microscopy technique based on a phase-contrast microscope setup extended into a pump-probe scheme. This methods enables a dynamic observation of the complex refractive index in the interaction region with a time resolution better than 300 fs. In optical transmission mode, the transient absorption coefficient can be measured for different illumination wavelengths (400 nm and 800 nm). The phase-contrast mode provides qualitative information about the real part of the transient refractive index. Based on the study of those transient optical properties, we observe the onset and relaxation of the laser-generated plasma into different channels such as defect creation, sample heating, and shockwave generation. The majority of our experiments were carried out with amorphous silica, but our method can be applied to the study of all transparent media.

Fused silica (a-SiO₂) exposure to low-energy femtosecond laser pulses leads to interesting effects such as a local increase of etching rate and/or a local increase of refractive index. Up to now the exact modifications occurring in the glass matrix after exposure remains elusive and various hypotheses among which the formation of color centers or of densified zones have been proposed. In the densification model, shorter SiO₂ rings form in the glass matrix leading to an enhanced etching rate. In this paper, we investigate quantitatively the amount of volume variation occurring in well-defined laser exposed areas. Our method is based on the deflection of glass cantilevers and hypotheses from classical beam theory. Specifically, 20-mm long cantilevers are fabricated using low-energy femtosecond laser pulses. After chemical etching, the cantilevers are exposed a second time to the same femtosecond laser but only in their upper-half thickness and this time, without a subsequent etching step. We observe micron-scale displacements at the cantilever tips that we use to estimate the volume variation in laser affected zones. Our results not only show that in the regime where nanogratings form (so called type II structures), laser affected zones expand but also provide a quantitative method to estimate the amount of stress as a function of the laser exposure parameters.

Fused silica (a-SiO₂) exposure to low-energy femtosecond laser pulses (below ablation threshold) introduces a local increase of the HF etching rate. This property has been used to fabricate a variety of structures ranging from simple fluidic channels to more complex optofluidics and optomechanical devices. In practice, the desire patterns are written by contiguously stacking laser exposed regions, which defined the volume to be removed.. In previous work, we showed that there was an optimum energy level for maximizing the efficiency of the etching process. Here, we focus on the interaction between adjacent laser affected zones and its effects on the overall etching process. Experimentally, we exposed fused silica specimens to patterns consisting of matrices of lines with varying density, under various laser exposure conditions. Surprisingly, we show that for certain laser affected zone densities and pulse energies, the exposed regions do not etch while their constitutive elements (i.e. the single laser affected zones) do. This paper describes our recent experimental observations and proposes a qualitative model to explain these findings.

Focused femtosecond laser pulses from a 1 MHz fiber laser were used to create modifications in Er- Yb doped zinc phosphate glass. Two glasses with similar phosphate glass networks but different network modifiers were investigated. To understand the resulting changes caused by the femtosecond laser pulses various characterization techniques were employed: glass structural changes were investigated with confocal Raman spectroscopy, defect generation as well as local Er and Yb environment were investigated with confocal fluorescence spectroscopy, and elemental segregation resulting from heat accumulation effects was ascertained by scanning electron microscopy.

Sensor chips to measure electrical signals of living cells are patterned with lasers from thin films of platinum as the conductive layer and tantalum pentoxide as the isolating layer. The selective ablations of the transparent tantalum pentoxide alone as well as the complete removal of both layers were investigated using picosecond laser pulses at different fluences. Ablation threshold values were measured for the irradiation either from the layer (front) side or from the glass (back) side. We observed complete and selective laser ablation of the films at low laser fluences.

The process of ultrashort laser-assisted selective removal of thin dielectric layers from silicon substrates has a large potential for technological applications, the most straightforward one being an energy-efficient and environmentally compatible method to produce contact openings on crystalline silicon solar cells. Using photon energies above the band gap energy, ablation of such thin transparent layers is possible without noticeable damage of the silicon substrate. To understand in detail the physics behind this damage-free delamination, experiments with a variety of laser parameters were done, utilizing in particular wavelengths from UV to mid-infrared and pulse durations between 50 and 2000 fs. Experiments were also conducted using different transparent materials on silicon, e.g. SiO₂ and Si_xN_y. The ablated regions were carefully analyzed by light microscopy (LM), atomic force microscopy (AFM), Raman spectroscopy (RS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The results give evidence that the mechanism of damage-free ablation is initiated by ultrafast creation of electron-hole plasma by the ultrashort laser pulse itself followed by non-thermal decomposition of an ultrathin Si layer of a few nm thickness only. This process works best in the region of moderate substrate absorption, i.e. using laser photon energies only slightly above the band gap, and for the shortest pulses. In contrast, laser energy input into the dielectric layer by addressing either the UV absorption or a vibrational resonance (e.g. at λ = 9.26 μm for SiO₂) allowed ablation only in connection with partial damage of the substrate.

Metal nanofabrication techniques have become increasingly important for photonic applications with rapid developments in plasmonics, nanophotonics and metamaterials. While two-dimensional (2D) techniques to create high resolution metal patterns are readily available, it is more difficult to fabricate 3D metal structures that are required for new applications in these fields. We present a femtosecond laser technique for 3D direct-writing silver nanostructures embedded inside a polymer. We induce the photoreduction of silver ions through non-linear absorption in a sample doped with a silver salt. Utilizing nonlinear optical interactions between the chemical precursors and femtosecond pulses, we limit silver-ion photoreduction processes to a focused volume smaller than that of the diffraction-limit. The focal volume is scanned rapidly in 3D by means of a computer-controlled translation stage to produce complex patterns. Our technique creates dielectric-supported silver structures, enabling the nanofabrication of silver patterns with disconnected features in 3D. We obtain 300 nm resolution.

The use of picosecond lasers for microstructuring, especially in the combination with scanner optics, leads to undesired effects with increasing ablation depths. The cavity edges slope to a degree ranging between 50° and 85°, depending on the material. With highly reflective substrates, ditches of up to 20% of their total depth can be formed on its ground structure. In certain materials also diverse substructures such as holes, canals, or grooves can be developed. These could impact the precision of the ablation geometry partially. A systematic study of the specific ablation characteristics is needed to achieve a defined depth of the structure. Considering a huge number of influential parameters, an automation of such measurements would be meaningful. For a study of eight different materials (high-alloy steels, copper, titanium, aluminum, PMMA, Al₂O₃ ceramics, silicon and fused quartz), an industrial ps-laser coupled with a chromatic sensor for distance measurement was used. Hence a direct acquisition of the generated structures as well as an automatic evaluation of the parameters is possible. Furthermore an online quality control and a local post processing can be implemented. In this way the generation of complex structures with a higher precision is possible.

We investigated the influence of the pulse duration on the laser drilling process in the femtosecond, picosecond and nanosecond regime by in-situ imaging of the hole formation in silicon for pulse energies from 25 μJ to 500 μJ. For percussion drilling, we used a Ti:Sa CPA laser system that provides pulses with a duration of 50 fs up to 10 ns at 800 nm. At this wavelength, silicon shows linear absorption and its ablation behavior is comparable to metals. The temporal evolution of the longitudinal silhouette of the hole was visualized during the drilling progress. Deep holes with a depth larger than 1 mm and aspect ratios up to 30:1 were generated. In terms of maximum achievable depth, ultrashort pulses with a duration below 5 ps show comparable efficiency for pulse energies below 100 μJ, while ns-pulses only lead to shallow depths. The situation changes for pulse energies higher than 100 μJ. The depth of holes drilled with ns-pulses increases linearly with pulse energy, while ultrashort pulses show a saturation of achievable depth, which is most distinctive for the shortest pulse duration of 50 fs. The increase in depth for ns-pulses is accompanied by an increasing number of pulses required to reach this depth, which can be 10 times as much as for ultrashort pulses at the same pulse energy. The drilling process consists of an iterative sequence of forward drilling and increase of hole diameter. The increase in diameter leads to numerous deviations from a cylindrical hole shape in the form of bulges, cavities and finger-like structures. This is less pronounced for ps-pulses. fs-pulses show the best achievable hole geometry at a tapered shape without noticeable deviations.

From the initial observation of self-channeling of high-peak power femtosecond (fs) laser pulses in air, propagation of intense ultrashort laser pulses in different media has become one of the most investigated research areas. The supercontinuum emission (SCE), a spectral manifestation of the spatio-temporal modifications experienced by a propagating ultrashort laser pulse in a nonlinear medium, has many practical applications. However, the extent of blue shift of SCE is reported to be constant due to the phenomenon of "intensity clamping". To further explore the recently observed regime of filamentation without intensity clamping, we measured the evolution of spectral blue shift of SCE resulting from the propagation of fs pulses (800 nm, 40 fs, 1 kHz) in distilled water under different focusing geometries. The efficiency of SCE from tight focusing (f/6) geometry was always higher than the loose focusing (f/12) geometry for both linear and circular polarized pulses. The blue edge of the SCE spectrum (λ_min) was found to be blue shifted for f/6 focusing conditions compared to f/12 focusing geometry. The lower bound of the intensity deposited in the medium measured from the self-emission from the filament demonstrated the existence of intensities ~ 6x10¹³ Wcm^-2, far beyond the clamping intensities achieved erstwhile.

Fundamental mode, ~100 ps, ~40 W optical pulses are demonstrated from a laser diode with a strongly asymmetric waveguide structure and a relatively thick (~0.1 μm) active layer driven with ~15 A, ~1.5 ns injection current pulses produced by a simple avalanche transistor circuit. Using this compact laser source, pulsed time-of-flight laser rangefinding measurements were performed utilizing a single-photon avalanche detector. The results show the feasibility of a very compact overall device with centimeter-level distance measurement precision and walk-error compensated accuracy to passive targets at tens to hundreds of meters in a measurement time of about ten milliseconds.

Ultrashort pulse laser systems are widely used in many areas such as microprocessing of various materials, the generation of terahertz radiation, nonlinear optics, medical tomography, chemistry, and biology due to the high peak power and large spectral width. For a practical usage of the femtosecond lasers, they must be fairly compact and stable. These conditions are most fully met when laser media are used that allow direct pumping with the radiation from semiconductor injection lasers, which are more compact, reliable, and inexpensive than pumping with solid-state lasers. Since Ytterbium-doped crystals have a broad luminescence band for generating femtosecond pulses less than 500 fs wide, they are attractive as materials for lasers with direct diode pumping. Moreover, the position of the central luminescence wavelength of Yb:KGW and Yb:KYW crystals makes them promising priming sources of femtosecond pulses for amplifiers that operate at wavelengths close to 1 μm (Yb:KGW, Yb-glass, Nd-glass, Yb:YAG, etc.) We developed a femtosecond generator based on the Yb:KYW crystal with direct pumping by the radiation of a laser diode with fiber output of the pump radiation. The use of such pumping, as well as of chirped mirrors to compensate intracavity dispersion, made it possible to generate a continuous sequence of optical pulses 90 fs wide at a frequency of 87.8 MHz with a mean radiation power of more than 1 W. The product of the pulse width by the spectral width is close to the theoretical limit, and this indicates that there is no frequency modulation.

The present study is undertaken in order to develop an automatic measurement system for light transmissibility of jointed transparent materials using high-rate-pulses ultrafast laser microwelding. To measure joint strength, it is necessary to measure the tensile strength and welded area quantitatively. Especially, the welded area greatly influences joint strength in the microwelding. Thus, it is important to distinguish the welded area and non-welded area. The welded sample was irradiated by He-Ne laser light, and the light, which passed through the welded sample, was detected by a photo detector. The transmitted light has two intensity levels because the transmissibly of light is different in the welded area and non-welded area of the welded sample. Wherein, the welded area and non-welded area are classified by irradiating the He-Ne light to the sample, and detecting the transmitted light. This technique is also applied to determine the accurate welded area after welding using various shapes such as spiral and rectangular, the relationship between joint strength and shapes will be presented.