This PDF file contains the front matter associated with SPIE Proceedings Volume 7201, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing

We have studied periodic nanostructure formation processes on hard thin film surfaces in femtosecond laser ablation. Using diamond-like carbon films patterned with submicrometer-size stripes, we found that the nanoscale ablation is preferentially initiated by the enhancement of a local field on the stripe surface having high curvature. Based on the experimental results for the initial stage of nanostructuring, it is concluded that the nanoscale ablation is initiated with the enhanced local field, and the periodicity is developed with the excitation of surface plasmon polaritons.

Manganese dioxide (MnO₂) is considered as one of the most attractive compound among the manganese oxide phases due to its fundamental chemical and physical properties, its use in energy-storage devices, electrochemical applications, and biosensors. There have been limited attempts to grow high quality MnO₂ thin films where high pressure and low substrate temperature are targeted to promote the formation of this phase. In this work, we have exploited the flexibility of Pulsed Laser Deposition (PLD) in order to synthesize thin films of MnO₂ on Si substrates by laser ablation of a MnO target in oxygen gas ambient. Substrate temperature was varied from 25 to 800 °C aiming to grow films of good crystalline quality while investigating the temperature range where MnO² phase is expected to be stable. We have also investigated the effect of oxygen pressure which was varied from 10 to 500 mTorr. X-ray diffraction and Fourier Transform Infra-Red analyses have confirmed the formation of the MnO² phase for pressures above 250 mTorr, and an optimal deposition temperature of 500 °C, while Mn₂O₃ is obtained in the range between 550 and 650 °C. Further increase in deposition temperature led to pure Mn₃O₄ films. Atomic Force Microscopy imaging confirms the nanograined surface structure of the MnO₂ films, with a typical grain size of 30 nm.

Nanoparticles are known to cause adverse health effects. But the generation of nanoparticles cannot be avoided during laser machining, especially ultrashort-pulsed laser ablation which releases a high share of nanoparticles. The nanoparticulate size fractions emitted during picosecond (ps) laser ablation are compared with those released during femtosecond (fs) laser ablation using steel, zirconia and brass. At the same pulse energy, fs pulses release similar share of nanoparticles (>80%) in the aerosol fraction, with fs compared to ps generating a far higher share of ultrasmall (7 nm) sized particles during machining of metals and ceramics. The frequency maximum corresponds to the particle size of 50 nm independently of the ablated material and applied pulse duration. During ps laser ablation the absolute nanoparticle emission rate is higher than during fs laser ablation, whereas the emission rate per pulse is two magnitudes lower. Finally, the nanoparticle emission rates and its nanoparticle surface equivalent for ps and fs laser micromachining of metal and ceramic are compared with inflammatory thresholds derived from toxicology studies. It would take more than 6.500 working days to exceed this theoretical threshold of inflammation during laser operation at 0.5-2W and at least 260 working days using high-power lasers.

This paper presents the first scribing results obtained by combining a short-pulse 10ns green laser with the water jet-guided laser technology. A number of high-potential applications are presented, from the grooving of low-k silicon wafers, the scribing of metallic and amorphous Si layers of thin film solar cells, the grooving of SiC wafers, and dot marking of Si wafers. The combination of a short pulse laser beam with the water jet-guided laser technology offers a new industry-proven alternative for grooving and scribing processes, providing superior speed and quality compared to legacy laser technologies.

By laser-induced backside wet etching (LIBWE), we can fabricate microfluidic channels on silica glasses. These channels have smooth bottom surfaces that can be combined with various optical detection techniques. Antiresonant guided optical wave (ARGOW) is a concept for guiding light in the system composed of a low refractive index medium surrounded by a medium with higher refractive index. The ARGOW was examined by using the wide channels (length: 17 mm, width: 1 mm, depth: 45 μm) prepared by LIBWE, whose bottom surface showed root-mean-square (RMS) roughness less than 100 nm. The LIBWE can fabricate deep trenches with high aspect ratio (~57 (length: 1mm, width: 10 μm, depth: 566 μm)). By using such deep channels, ARGOW system within a plane parallel to the top surface of glass can be fabricated. In this work, surface roughness of the sidewall of deep trenches prepared with LIBWE was evaluated, and the possibility of utilization for guiding light is discussed.

Presently lasers are well established tools for materials processing due to advantages such as (i) the non-contact nature of the laser-material interaction, (ii) the high precision achievable and (iii) no requirement for high vacuum equipment or costly chemicals. Now, industrial laser users demand improvements in order to achieve higher quality features with reduced heat affected zones and so it is increasingly necessary to use shorter pulse durations. To satisfy these needs, there has been significant research into ultrafast laser technology for decades, however at this time, these lasers have yet to be adopted by industry for mass production. Recent developments have shown that the combination of a fibre seed oscillator and Diode Pumped Solid State (DPSS) amplifying technology can offer high average power, picosecond pulses (~10ps) in an industrially-rugged package. The significant laser design aspects are outlined here, along with the advantages this technology offers for applications such as silicon via drilling, thin film patterning and the machining of wide bandgap materials.

Nanosecond class lasers have been the mainstay of optical machining for decades, delivering pulses with high fluences (>1 J/cm²) that cause many material sets to undergo thermally-induced phase changes to cause removal of matter. While in many cases their delivery of sheer laser power has proved useful, nanosecond lasers have fallen short of addressing current micromachining requirements with respect to decreased feature sizes and more complex substrates. One main issue is the laser pulse width endures throughout the ablation process, depositing energy is deposited into plasma formation and local material heating. Plasma shielding takes place when the laser pulse energy contributes to plasma formation to a greater extent than direct material ablation processes. The result is a crude "plasma cutter" of the substrate, leaving a telltale trail of localized dross and droplet deposition. Nanosecond lasers of sufficient process speeds are typically Q-switched with repetition rates less than 200 kHz. As a result, the scribed lines are made of a sequence of "blast events" that result in a variety of undesired consequences and a limited process speed.

Using a commercial laser system operating at a 532 nm wavelength with 10 ps pulses, experiments were conducted on polished metal samples to study material removal characteristics from a low number of laser pulse exposures. The samples were analyzed with a scanning electron microscope and white light interferometer to gather data on surface deformation and material removal. The effects of energy and various double pulse machining methods were examined. The results from changing the pulse separation for double pulse drilling are compared to prior work with picosecond and nanosecond pulse lasers.

Time-resolved phase distributions of laser-induced breakdowns generated by two pulses in water are observed with a pump-probe interference microscope. When the two pulses are overlapping temporally, the optical interference of the two pulses are resulted in fluctuation of pulse energy used to breakdown. When shock waves emitted from breakdowns are overlapped, the pressure of overlapping point is addition of the pressure of each shock wave. When two pulse is overlapping spatially, even temporally separated, a nonlinear enhancement of shock wave is observed. It may be caused by an interaction between a plasma and a post pulse.

We present some small optical instruments fabricated with femtosecond laser pulses. These instruments, made from monolithic fused silica substrates, incorporate an extensive collection of optical and micro-mechanical elements. A single manufacturing step was used to define both the optical and the mechanical features. This approach dramatically simplifies overall fabrication and eliminates alignment issues associated with sequential fabrication processes. Potential applications and technical challenges are reviewed.

Two-photon polymerization (TPP) is an enabling technology that allows fast prototyping of parts with sub-100 nm resolution. Due to its ability to fabricate microstructures with arbitrary three-dimensional geometries, TPP has been employed in diverse fields such as photonics, microelectronics, microelectromechanical systems, and microfluidics. However, no information is available to date that microscopically correlates the experimental conditions used in TPP with the properties of the ultimate microstructure. We present a study where the distribution of polymer cross-linking in three-dimensional microstructures fabricated by TPP is visualized by means of nonlinear microscopy. In particular, coherent anti-Stokes Raman scattering (CARS) microscopy is employed to image polymer microstructures with chemical specificity. The characterization of the microstructures based on the acquired images permits rational optimization of the TPP process.

Laser interference lithography (LIL) is concerned with the use of interference patterns generated from two or several coherent beams of laser radiation for the structuring of materials. This paper presents the work on the processes based on resists and direct writing with laser interference lithography. In the work, a four-beam laser interference system was used as a submicrometer structuring tool in which a high-energy pulsed, frequency-tripled and TM polarized Nd:YAG laser (355 nm) with a coherent length of 3 m, energy power up to 320 mJ/cm², pulse duration of 8 ns and 10 Hz repetition rate was used as a light source. The experimental results were achieved with 2-beam and 4-beam interference patterning. The processes can be used to define submicron surface relieves in large areas for use in the field of MEMS.

Bimetallic thin films of Bi/In and Sn/In oxidize becoming transparent under laser exposure. By controlling the laser power, direct-write binary and grayscale photomasks can be produced with the mask's transparency, or optical density (OD), ranging between ~3.0 (unexposed) to <0.22 OD (fully exposed). An OD measurement system has been developed that provides real time OD and laser exposure power measurements while the masks are being written. Measurements are obtained for each combination of films, characterizing their response when patterned with a raster-scanned v-groove mask. The characterization is performed by writing v-groove step patterns and modifying the mask's writing parameters such as velocity, line spacing and step width. Stationary results demonstrate Sn/In takes longer to expose compared to Bi/In. With a moving beam, the oxidation of Sn/In also occurs over a wider power range suggesting film materials with delayed or slower oxidations may offer power ranges that are better suited for grayscale masks. A narrow power range is less desirable for grayscale as more control is required over the writing laser. The stationary exposures also demonstrate both films can produce >64 distinct OD levels provided there is sufficient control over the laser power and exposure duration. The physical characteristics of the films are also examined to determine a more accurate method of verifying each film's composition. Combining weight, area, and thickness measurements allows for better characterization of the films as the thickness for bi-layer films are found to differ significantly from the sum of the individual layers.

In the development of extreme ultraviolet (EUV) light source at 13.5 nm for EUV lithography system by laser-produced plasma (LPP), a Tin (Sn) micro-droplet target is considered as a one of the promising targets for debris mitigation. In addition, double pulse irradiation scheme is regarded to be effective in order to improve the conversion efficiency to EUV light in the use of the droplet target. In our study, the dynamics of debris from the Sn droplet target irradiated by double pulses was investigated in order to establish the guideline for the optimum design of the mitigation system. The kinetic behaviors of the Sn atoms and of the dense particles from Sn droplet target irradiated by double pulses from the Nd:YAG laser and the CO₂ laser were investigated by the laser-induced fluorescence imaging method and a high-speed imaging, respectively. After the pre-pulse irradiation of the Nd:YAG laser, the Sn atoms were ejected in all direction from the target with a speed of as fast as 20 km/s and the dense particle cloud expanded by a reaction force due to the plasma expansion with a speed of approximately 500 m/s. The expanding target was subsequently irradiated by the main-pulse of CO₂ laser and the dense cloud was almost disappeared by main-pulse irradiation.

It has been shown that the laser shock cleaning (LSC) process is effective for removing nanoscale particles from solid surfaces and thus has various potential applications in microelectronic manufacturing. In this work, we propose a simple method to amplify the shock wave intensity generated by laser-induced breakdown (LIB) of air. The suggested scheme employs a plane shock wave reflector which confines the plasma expansion in one direction. As the half of the LIB-induced shock wave is reflected by the reflector, the intensity of the shock wave propagating in the opposite direction is increased significantly. Accordingly, the enhanced shock wave can remove smaller particles from the surface than the existing LSC process. The LSC process under geometrical confinement is analyzed both theoretically and experimentally. Numerical computation of the plasma/shock behavior shows about two times pressure amplification for the plane geometry. Experiments confirm that the shock wave intensity is enlarged by the effect of geometrical confinement of the plasma and shock wave. The result of cleaning tests using polystyrene particles demonstrates that the particle removal efficiency increases by the effect of geometrical confinement.

This work presents a new method for ultra-fast laser marking using nano-structures as well as a suitable method of reading. These nano-structures, called ripples, are an irregular grating with a controllable orientation. It is possible to observe these ripples and theirs orientations with differents acquisitions systems. The one we chose to use is a scanner. It is possible to have an ripples' orientation matching one of the colors in the image acquisition. This feature allows us to consider new applications for marking and new types of identifying code.

A microchip made of UV transparent polymer (CYTOP) that can perform selective cell culture has been fabricated by F₂ laser surface modification. The refractive index of CYTOP is almost the same as that of culture medium, which is essential for three dimensional (3D) observation of cells. The F2 laser modification of CYTOP achieves hydrophilicity only on the laser irradiated area with little deterioration of the optical properties and surface smoothness. After the laser modification, HeLa cells were successfully cultured and strongly adhered only on the modified area of CYTOP. The cells patterned on CYTOP were applied for clear 3D observation using an optical microscope in phase contrast mode.

The development of high-reflection multilayer mirrors in the "water window" (λ=2.3-4.4nm) is desired for attosecond soft x-ray optics. TiO₂/ZnO multilayer mirrors were proposed in this study as highly reflective coatings for the water window wavelength region. The theoretical calculation on the layer combination indicated that the high reflectivity of approximately 50% at 2.73 nm was obtainable at the incidence angle of 18.2° from the normal incidence. The ZnO and TiO₂ thin films were grown using atomic layer epitaxy (ALE) methods at 450°C. Experimental results indicated that both the crystalline rutile TiO₂ (200) and wurtzite ZnO (0001) thin films both were grown epitaxially on Al₂O₃ (0001) substrates by ALE. Moreover, a 10-bilayer TiO₂/ZnO multilayer showed the soft X-ray reflectivity of around 10%.

Optically excited single-walled carbon nanotube exciton dynamics are predicted using a stochastic model including linear and nonlinear decay pathways. Results are fitted to the photoluminescence behavior of a single 4-μm long airsuspended (9,8) single-walled carbon nanotube. Hard photoluminescence saturation is observed even with only a few excitons are present in the single-walled carbon nanotube. The absorption coefficient is estimated to be 0.01 - 0.04, and photoluminescence quantum efficiency is 13%. Femtosecond excitation correlation spectroscopy dynamics are consistent with linear and nonlinear (exciton-exciton annihilation) lifetimes of 80 ps and 0.8 ps respectively.

The removal of thin films widely used in photovoltaics as (transparent) electrodes (e.g. SnO₂, molybdenum) or solar absorber (e.g. amorphous silicon) materials is studied experimentally using multi-kHz diode-pumped solid state lasers in the visible and infrared spectral region. The film processing (or what is commonly known as P1, P2, or P3 laser scribing) is performed through the film-supporting glass plate of several millimeter thickness by using a galvo laser scanner setup equipped with f-theta optics. The dependence of the film removal fluence threshold on the laser pulse duration (~8 ns to ~40 ns) is investigated systematically for two different laser wavelengths of 532 nm and 1064 nm. The laser-scribing of continuous lines suitable for thin-film solar cell production is demonstrated successfully at scribe speeds on the order of meters per second. The experimental results are discussed on the basis of laser ablation models considering optical, geometrical, and thermal material properties and are additionally supported by numerical simulations.

An integrated tool combining control and diagnostic for nanoprocessing of bio-compatible and biological materials and also allowing multiphoton large area laser scanning microscopy has been developed. The device is based on an customized inverted microscope integrating a motorized open x,y stage with a very high precision and repeatability, a piezoelectric z axe. A strong development in hardware and software has been made for the control of the process. Imaging of large area by images reconstruction using a high resolution CCD camera for the machining and perforation of biological materials and non-biological materials on scales in the sub-micrometer range is possible. This tool can also be used as a laser scanning microscope of a large area using a PMT detector. This multi-function compact device is of prime interest and can be considered as a novel tool for nanoprocessing in material science, nanobiotechnology, nanomedicine. Further progress in telecommunications, optics, electronics, biomaterials, medicine, and transport strongly depends on the availability of reliable and rapid processing techniques. Laser-based micro-nano technology holds great promises and the evolution will be dictated by the development of inexpensive yet precise processing tools that can develop and structure materials with a high degree of controllability, accuracy, and reduced residual damage. Applications in biomedicine include, for example, optoporation, cells nanodrilling, nanocutting transfection of cells, deactivation of cell organelles or investigation of cell dynamics but also potentially useful in material science for the manufacture of waveguides, gratings, micro fluidic devices, nanocontainers, data storage, nanolithography, nanomarking,...

Transmission and luminescence spectra of natural or/and synthetic samples of corundum, diamonds and phianites are obtained by irradiation of a KrCl-excilamp (222 nm) driven by the barrier discharge. It is offered to use a KrCl-excilamp for development of devices for nondestructive identification of diamonds and their imitations.

A windowless excilamp, a xenon excilamp with the high specific power of radiation and an air-cooling KrCl excilamp for microelectronic applications are described. The excilamps have the total radiating surface up to 900 cm². The VUV specific average power of a windowless excilamp is 3 mW/cm² and 5 mW/cm² for argon (λ ~ 126 nm) and krypton (λ~146 nm) accordingly at distance of 3 cm from the emitting surface. The xenon excilamp (λ ~ 172 nm) has 50 W of the average total VUV power and 120 mW/cm² of density and the large-aperture air-cooling KrCl (λ ~222 nm) excilamp has 30 mW/cm² of the radiation density and the radiation homogeneity 12 %.

We fabricated indium tin oxide (ITO) thin films on nanoimprinted glass substrates using pulsed laser deposition (PLD). The nanoimprinted glass substrate was prepared by thermal nanoimprint using an atomically stepped sapphire (α-Al₂O₃ single crystal) mold. Two kinds of sapphire molds were employed, one with a single step about 0.2 nm high and the other with a bunched step about 2 nm high. The surface morphology of the stepped sapphire mold was successfully transferred to the glass surface in an atomic scale. The nanoimprinted glass had a regular nanostepped pattern; one had a step height of about 0.2 nm and step separation of about 100 nm, the other had a step height of about 2 nm and step separation of about 1 μm. The ITO films were deposited at room-temperature (RT) or 200°C on the nanoimprinted glass substrates and on the non-patterned commercial glass for comparison. The ITO films deposited at RT were post-annealed for further crystallization. The surface of the ITO thin films deposited on the nanoimprinted glass well reflected the nanopattern of the glass substrate surface. Preferential crystalline orientation of the ITO thin films was achieved on the nanoimprinted glass substrates. The resistivity of ITO thin films deposited on the nanoimprinted glass was lower than that on the commercial glass, which was probably due to the higher crystal orientation of the films grown on the nanoimprinted glass surfaces.

We present results of comparative study of laser-induced ablation of AlN films with variable content of oxygen as a surface-doping element. The films deposited on sapphire substrate were ablated by a single nanosecond pulse at wavelength 248 nm, and by a single femtosecond pulse at wavelength 775 nm in air at normal pressure. Ablation craters were inspected by AFM and Nomarski high-resolution microscope. Irradiation by nanosecond pulses leads to a significant removal of material accompanied by extensive thermal effects, chemical modification of the films around the ablation craters and formation of specific defect structures next to the craters. Remarkable feature of the nanosecond experiments was total absence of thermo-mechanical fracturing near the edges of ablation craters. The femtosecond pulses produced very gentle ablation removing sub-micrometer layers of the films. No remarkable signs of thermal, thermo-mechanical or chemical effects were found on the films after the femtosecond ablation. We discuss mechanisms responsible for the specific ablation effects and morphology of the ablation craters.

We report on a new waveguide fabrication method with femtosecond laser pulses shaped by Computer-Generated Hologram (CGH). We design and make CGH's that generates a straight-line intensity distribution from an input laser intensity distribution. We fabricate a waveguide inside a fused silica sample with exposing the line intensity beam generated by the CGH, without translating the sample. The fabricated waveguide is 5.1 mm long and 6μm width. We also observe guided-light passing through the waveguide that is butt-coupled to a single mode fiber, at wavelength of 635 nm. The near field pattern is nearly circular cross section. This is the first achievement of waveguide fabrication using a CGH.

Femtosecond laser processing acquires futures of high throughput and high light-use efficiency by using a computer-generated hologram. In the holographic femtosecond laser processing, a precise control of diffraction peaks is indispensable to fabricate enormous numbers of nanometer-scale structures simultaneously. The computer-optimized hologram has high uniformity of the diffraction peaks in the computer reconstruction. However, the uniformity decreases due to spatial and temporal properties of the optical system. We propose some optimization methods of the hologram to improve the uniformity and demonstrate the processing performance.

Top down technology of ultra-short pulse laser processing was applied to induce liquidly process and generate new nanostructures such as nano-waterdrop, nanocrown, and fine web structure. For example, a nano-waterdrop was generated by a single shot ps laser irradiation and had the narrow dieter of about 50 nm. In the case of nanocrown, whiskers were standing at the edge of a nanohole, and the diameter of the whiskers was around 100 nm. In addition, wavelength-sized web structure was generated in a single shot of femtosecond laser irradiation.

We studied the spectral shift of random lasing in the Rhodamine 6G dye solution with TiO₂ nanoscatterers under picosecond pulses pumping. The red shift, resulting from the re-absorption and re-emission of the dye, indicates a longer optical path length of the emitted laser traveling inside the medium. Thus the optical paths of the random laser in the solution can be estimated using the values of red shifts for different dye concentrations and scatterer densities. The diffusion theory is provided and the theoretical results agree very well with that calculated from the red shifts before the inflection points appear for increasing scatterer density. The followed increasing scatterer density results in the lights staying longer in the medium, in contrast to that predicted by the diffusion theory. So it is clear that the inflection point shows that the system is changing from a diffusion system to a weakly localized one in which the light stay longer because of the localization.

We present time-resolved measurements of pulse transmission at wavelength 532 nm (60 ps pulse width, 10 Hz repetition rate) on samples of titanium powders suspended in methanol. The average particle diameter of the powders is 80 nm. We used a streak camera with 2 ps time revolution to record the transmitted signals. When the particle density is low, the results agreed with the diffusion theory and we obtained the time-independent diffusion constants. By adding the titanium powders gradually in methanol, we obtained the relationship between the diffusion constant and the particle density of TiO₂ in the suspended solution. When using the TiO₂ powders as the sample with a particle density of 1.36x10¹⁵ cm^-3, the experimental result showed a little deviation from the diffusion theory, which may be the signature of localization in the random media.

Many micro- and nanoelectronic, micro- and nanooptic devices include different films and layers deposited at the surfaces of dielectric substrates. Properties of these films and layers sufficiently depend on properties of the substrate surface. Therefore substrate surface preparation before layers and films deposition is very important. One of the main parameters of the surface is its roughness that influence on such parameters of thin layers as specific resistance, electric strength, chemical resistance etc. By mechanical treatment of the surface its roughness is defined by the size of polishing powder grain. That is why preparation of the surface with low roughness is laborious one. Besides, preliminary mechanical grinding with coarse-grained powder causes appearance of near-by-surface cracked layer, which can be removed by deep mechanical, chemical or flame polishing. Laser polishing is sort of last one. The problem of laser polishing was repeatedly discussed. 10.6 μm CO₂-laser is the only acceptable one, as all glasses well absorb radiation at this wave length. The regime of continuous radiation is used in most cases, for which typical duration of influence by surface scanning is several milliseconds. Though the beneficial effect was obtained (in before mentioned and other papers), the technique is not wide spread. In our opinion the reason of this is that there are problems connected with phenomena specific for laser polishing: hydrodynamical waves in the softening layer and thermomechanical tensions in the substrate. Both of them are aggravated by the three-dimensional locality of laser action. This situation can be changed by using of short nanosecond laser pulses - in this case the heated layer of substrate decreases and the problem becomes not so critical.