This PDF file contains the front matter associated with SPIE Proceedings Volume 7920, including the Title Page, Copyright information, Table of Contents and the Conference Committee listing.

Mass resolved time-of-flight measurements on neutral zinc atoms and zinc ions show energetic ions and neutrals during 193-nm irradiation of single crystals of semiconducting zinc oxide. Typical Zn⁺ kinetic energies are 3-5 eV. At fluences (energy per unit area per pulse) below 200 mJ/cm², the ion intensities (per laser pulse) decrease monotonically to low values with laser pulse number. The depletion kinetics change from exponential to second order near 50 mJ/cm². We attribute this change to the annihilation of defects yielding Zn⁺ emission when Zn⁺ or other surface defects become mobile. At fluences between 200 and 300 mJ/cm², Zn⁺ emission becomes more sustained due to defects created by the laser. In this same fluence range, we observe the onset of detectable neutral atomic zinc emission. These neutral atoms display Maxwell-Boltzmann kinetic energy distributions with effective surface temperatures that approach 5000 K as the fluence is raised to 350 mJ/cm². These high surface temperatures are remarkable given the low etch rates observed at these fluences, suggesting that heated layer is extremely thin. We propose emission mechanisms and experiments to resolve outstanding questions.

We present experimental and theoretical investigations of interaction of a femtosecond laser (450 fs pulse at 1025nm) with dielectric materials (fused silica) for the single-shot laser regime. The aim is to analyze and understand the complex physical mechanisms of laser energy absorption yielding to damage and /or ablation. We outline the distinction between the ablation and the damage thresholds for dielectric materials. The evolution of the reflection, transmission and absorption signals is studied as a function of fluence. The experimental curves are accompanied by a modelling, which takes into account the photoionization and avalanche ionization depicting absorption of the laser energy by the material. The incident pulse propagation into the material, the temporal evolution of the electron density, reflection and transmission illustrate the beginning and the duration of the laser pulse absorption. The magnitude of the absorption process is energy density sensitive and, with the increase of the deposited fluence, the onset of absorption is moved temporally to the beginning of the pulse. We show the influence of the effective electron collision frequency on the calculated values of reflection, transmission and absorption. The results are particularly relevant to high micromachining industrial processes.

Optical imaging systems are widely used in different applications include tracking for portable scanners; input pointing devices for laptop computers, cell phones, and cameras, fingerprint-identification scanners, optical navigation for target tracking, and in optical computer mouse. We presented an experimental work to measure and analyze the laser speckle pattern (LSP) produced from different optical sources (i.e. various color LEDs, 3 mW diode laser, and 10mW He-Ne laser) with different produced operating surfaces (Gabor hologram diffusers), and how they affects the performance of the optical imaging systems; speckle size and signal-to-noise ratio (signal is represented by the patches of the speckles that contain or carry information, and noise is represented by the whole remaining part of the selected image). The theoretical and experimental studies of the colorimetry (color correction is done in the color images captured by the optical imaging system to produce realistic color images which contains most of the information in the image by selecting suitable gray scale which contains most of the informative data in the image, this is done by calculating the accurate Red-Green-Blue (RGB) color components making use of the measured spectrum for light sources, and color matching functions of International Telecommunication Organization (ITU-R709) for CRT phosphorus, Tirinton-SONY Model ) for the used optical sources are investigated and introduced to present the relations between the signal-to-noise ratios with different diffusers for each light source. The source surface coupling has been discussed and concludes that the performance of the optical imaging system for certain source varies from worst to best based on the operating surface. The sensor /surface coupling has been studied and discussed for the case of He-Ne laser and concludes the speckle size is ranged from 4.59 to 4.62 μm, which are slightly different or approximately the same for all produced diffusers (which satisfies the fact that the speckle size is independent on the illuminating surface). But, the calculated value of signal-tonoise ratio takes different values ranged from 0.71 to 0.92 for different diffuser. This means that the surface texture affects the performance of the optical sensor because, all images captured for all diffusers under the same conditions [same source (He-Ne laser), same distances of the experimental set-up, and the same sensor (CCD camera)].

Glass welding by ultra short laser pulses is a highly promising method to fusion weld glass pieces since it does not need an absorber or pre- and post-heating processes when compared to other laser fusion welding processes. This method utilizes strongly focused ultra short pulses that generate localized plasma which heats and melts the adjacent material. If the plasma region is sufficiently localized the stresses induced by plasma and heat can be tolerated so that defect-free joining of the brittle glass material can be accomplished. This paper gives an overview on the process and shows the advantages and limitations of this joining technology. A method that allows to determine the bonding energy of the welding seams is presented along with measurement results.

The reliability of copper welds is still a problem today concerning the high demands of spot or contact welding for the electronic or medical industry. Due to the low absorptivity at wavelengths of 1 micron and the very high thermal conductivity of copper, even small surface contaminations lead to drastic variations in weld quality. The wavelength of 532 nm (frequency-doubled Nd:YAG laser) is much better absorbed by copper at room temperature. Combining the two wavelengths and using the drastic increase in absorption with increasing temperature leads to an efficient spot welding solution. By the use of intelligent pulse forming with the thermal pulses of a Nd:YAG laser the spot weld reliability is improved significantly. This paper discusses a solution where Nd:YAG laser pulses composed of 85 - 90% of 1 micron and 10 - 15% of 532 nm radiation are used for spot welding of 80 - 300 micron thick copper ribbons. A weld spot diameter variation below 6% combined with 100% full penetration welding is achieved. The process efficiency is improved by more than a factor of two compared to conventional spot welding with 1 micron radiation.

Master Oscillator Power Fiber Amplifier lasers (MOPFA) lasers have been available for several years but very short nanosecond pulses along with low brightness, high repetition rates and high average power has only been achieved recently. The different types of pulsed fiber lasers are described. These new fiber laser designs have characteristics that allow them to challenge conventional laser technology in many application areas. Some data on industrially relevant ablation rates is included and other applications are also presented.

The potential of pulsed laser system in the range of 10ps to 100ps pulse duration for material processing has been further investigated. In detail the dependency of the volume ablation rate, penetration depth and threshold fluence on the pulse duration and number of pulses applied to the material will be discussed. The experimental results show that in the case of copper and steel, better results in quality and efficiency of the ablated material are achieved with shorter pulse durations.

Interfering femtosecond laser can induce periodic induction of energy on a thin film deposited on a substrate, and periodic thermal process is induced. This results in liquid motion of target, such as melting, inflation, flow and shrink, and then it freezes due to temperature fall by thermal radiation and conduction. The resultant structures are nanobump, nano-whisker, nano-waterdrop, nano-crown, and the shapes can be controlled by laser fluence, thin film thickness, substrate material, etc.. The size of some structures is smaller than 10 nm in curvature radius, and the aspect ratio is over 20. In addition, duplicated structure of two shapes, or double density structures can be generated in a single shot of laser irradiation by controlling the phase shift and power ratio between interfering beams. In the case of duplicated structure, the density of nano-structures is doubled, and two different nano-structures appear alternately. These structures will be useful in nanotechnology, especially in meta-material technology.

Successful fabrication of devices from quantum well-intermixed material requires efficient control of its surface morphology. To address this problem, we have employed atomic force microscopy to study surface morphology of InP/InGaAs/InGaAsP QW microstructure coated with dSiO₂ = 50, 150, 190, 243 and 263 nm thick SiO₂ films. Both ArF (193 nm) and KrF (248 nm) excimer lasers have been used to irradiate series of samples with up to 400 pulses of fluence 76 to 156 mJ/cm². The roughness (σRMS) of SiO₂ layer after both lasers irradiation and RTA decreases as the pulse number increases. Following RTA, a smoother surface morphology was observed for all irradiated samples. The cap InP layer was found to have a relatively smaller roughness (~ 0.4 nm) due to the protection provided by the SiO₂ layer during excimer laser irradiation and high temperature RTA. For samples coated with 50- or 150-nm-thick SiO₂ and irradiated by the ArF laser, the blueshift is only obtained when the SiO2 layer was ablated. However, the sample coated with 243-nmthick SiO2 (d_SiO2 ≈ λKrF), following the 75-pulse-irradiation with the KrF laser at 124mJ/cm² and RTA, showed a smooth surface (σRMS = 1.8 nm) and maximum blueshift of 74 nm achieved without removal of the SiO₂ layer.

Sintering of palladium (Pd) and silicon (Si) nano-particles (NPs) by a 266nm laser pulse train on ink-printed films was investigated. Organic Pd-ink, and organic Si-ink were used as precursors. A high repetition rate DPSS laser (up to 300 kHz, 25ns, 266nm, Coherent AVIA series), which produces a ns pulse train with 3.3 μs -33.3 μs interval of pulse-topulse, was used as the heating source. Highly electrically conductive Pd (Resistivity=~150μΩ·cm) thin film on PET substrate and semi-conductive Si (Resistivity=~23kΩ·cm) thin film on glass substrate were successfully obtained with this laser pulse train sintering process. The sintered films were characterized by AFM, SEM, TEM and Raman spectroscopy, respectively. The pulse train heating process was also numerically simulated.

Fabrication of textured poly-crystalline silicon films from amorphous-silicon (a-Si) films using a line beam is investigated. The mechanism of laser annealing and simultaneously form a nano-textured surface using an Nd³⁺: YAG laser at a wavelength of 355 nm with a line beam is discussed. Amorphous-Si films coated on glass and crystalline silicon substrates were treated with different laser fluence from 100 to 600 mJ/cm² and with 90% beam overlap. The crystallization and texturization characteristics were analyzed through SEM, Raman Spectroscopy, AFM, resistance and absorbance measurements. Generation of polycrystalline textured peaks was confirmed with different characterization methods and compared with the results of the conventional circular beam. This approach of line beam with increase in the scanning speed will allow the faster production of polycrystalline silicon from a-Si for photovoltaic application.

We report on the formation of characteristic surface features on Si(100) surfaces, which were generated by 85 MHz, sub-15 fs pulsed Ti:Sapphire laser light at a centre wavelength of 800 nm. With the Si(100) surface immersed in water, the high peak intensity in the tight focus of a high-numerical aperture objective resulted in profound structural and compositional surface modification at a periodicity of 1.0 μm. Oxide particles were formed at pulse energies below 0.3 nJ, whereas sub-10 nm hole arrangements surrounded by elevated areas were found at even lower focal intensities. The period of structural modulation was independent of the polarization of the laser light. On removal of SiO₂ by hydrofluoric acid etching, the silicon surface revealed tiny rifts oriented perpendicular to the direction of polarization, which were produced at near-threshold intensities at a period of 130 nm. In areas of higher exposure a random arrangement of structural elements of typically 20 nm in size was observed. In contrast, with the sample immersed in oil significant structural change of the Si(100) surface was not induced. However, filaments of carbon compounds at a diameter of approximately 100 nm were deposited periodically in the illuminated area.

In holographic femtosecond laser processing, a precise control of the diffraction peaks generated by a computergenerated hologram (CGH) displayed on a liquid crystal spatial light modulator is very important. We developed some design methods of the CGH. We developed a method that the CGH was optimized with based on an optical measurement of the diffraction peak intensities. Recently we also developed the second harmonic optimization based on the second harmonic generations induced by parallel femtosecond laser pulses. In our presentation, our recent progresses of the CGH optimization for holographic femtosecond laser processing are demonstrated.

Lasers can uniquely be used to create physical changes inside a bulk material. Traditional manufacturing processes are limited to surface modifications, but a laser can be focused at any location inside a material transparent to that wavelength. Using sub surface machining methods with ultrashort pulse lasers two practical applications are demonstrated. First, a laser is used to sever short-circuited wires embedded deep inside a thick piece of glass, effectively repairing a defective wire network. Second, subsurface bar-coding was shown to produce readable markings. Surface laser markings were shown to weaken the glass, but subsurface marking had virtually no effect on strength.

Chemically strengthened glass is finding increasing use in handheld, IT and TV cover glass applications. Chemically strengthened glass, particularly with high (>600MPa) compressive stress (CS) and deeper depth of layer (DOL), enable to retain higher strength after damage than non-strengthened glass when its surface is abraded. Corning Gorilla® Glass has particularly proven to be advantageous over competition in this attribute. However, due to high compressive stress (CS) and Central Tension (CT) cutting ion-exchanged glass is extremely difficult and often unmanageable where ever the applications require dicing the chemically strengthened mother glass into smaller parts. We at Corning have developed a CO₂ laser scribe and break method (LSB) to separate a single chemically strengthened glass sheet into plurality of devices. Furthermore, CO₂ laser scribe and break method enables debris-free separation of glass with high edge strength due to its mirror-like edge finish. We have investigated laser scribe and break of chemically strengthened glass with surface compressive stress greater than 600 MPa. In this paper we present the results of CO₂ scribe and break method and underlying laser scribing mechanisms. We demonstrated cross-scribe repetitively on GEN 2 size chemically strengthened glass substrates. Specimens for edge strength measurements of different thickness and CS/DOL glass were prepared using the laser scribe and break technique. The specimens were tested using the standard 4-point bend method and the results are presented.

Theoretical and experimental results concerning the use of axicons for laser-ablation are reported. Analytical formulas allow to predict the generated fluence distributions and the expected ablation widths. The influence of an imperfect axicon tip is discussed. The long depth of focus of the generated beam enables easy small-sized laser marking in dimension of the laser wavelength.

In this paper, next generation 780nm monolithic individually addressable 8 beam diode laser with 10mW optical power for laser scanning unit were developed. Beam to beam spacing is 30μm and air bridge interconnection process was developed for individual operations. Measured average values of threshold current(Ith), operating current(Iop), operating voltage(Vop), slope efficiency(SE), horizontal beam divergence(FFH), vertical beam divergence(FFV), and peak wavelength(λ) from 5 specimens are 14.91mA, 28.79mA, 1.91V, 0.72mW/mA, 8.28°, 31.89°, and 785.67nm respectively. Major electro-optic parameters from 8 emitters are within 3% variation for each device. Also we measured power droop that had a strong influence on printing image at 600Hz with duty 10% and 90% and we can obtained droop rate within 2% in each channel at room temperature and 10mW power. From 500Hr reliability life test result at 70°C, we obtained Iop variation within 1% in each channel with 10mw power. From the experimental measurement results, we can assure that the developed 8 beam diode laser is suitable optical source for high speed laser scanning unit in multi-function printing system and laser beam printers.

As electronic devices shrink in size to reduce material costs, device size and weight, thinner material thicknesses are also utilized. Feature sizes are also decreasing, which is pushing manufacturers towards single step laser direct write process as an attractive alternative to conventional, multiple step photolithography processes by eliminating process steps and the cost of chemicals. The fragile nature of these thin materials makes them difficult to machine either mechanically or with conventional nanosecond pulsewidth, Diode Pumped Solids State (DPSS) lasers. Picosecond laser pulses can cut materials with reduced damage regions and selectively remove thin films due to the reduced thermal effects of the shorter pulsewidth. Also, the high repetition rate allows high speed processing for industrial applications. Selective removal of thin films for OLED patterning, silicon solar cells and flat panel displays is discussed, as well as laser cutting of transparent materials with low melting point such as Polyethylene Terephthalate (PET). For many of these thin film applications, where low pulse energy and high repetition rate are required, throughput can be increased by the use of a novel technique to using multiple beams from a single laser source is outlined.

The growing demand for laser micro fabrication drives further requirements on higher production speed per part and lower manufacturing costs. A newly developed 1.2 kW 308 nm excimer laser addresses both micro-manufacturing and high production throughput. Solid state UV laser sources usually cannot emit UV laser radiation directly. The inherently required frequency conversion limits the total output power to several 10 Watts below 350 nm. Furthermore these UV-conversion- modules limit the long term reliability of high power UV solid state lasers significantly because of the wear of the conversion crystals. Excimer lasers, however, overcome these issues by direct emission at 308, 248, or 193 nm. By now up to 540 Watts at 308 nm are established in production. With the new laser we have more than doubled the available output power to 1.2 kW. The combination of short wavelength and highest available UV laser power makes it ideal for processing of small features or to modify thin surfaces. Furthermore, pulsed UV laser radiation is very suitable for removing delicate electronic devices from manufacturing substrates. High-power UV laser systems are capable of processing large areas with resolution down to several microns in one single laser ablation step without using multiple lithography and wet chemical processes. For instance, laser Lift-Off and large area annealing have proven to be very efficient manufacturing techniques for volume production. In this paper, a novel 1.2 kW excimer laser will be presented and discussed.

A femtosecond laser processing system with a spatial light modulator (SLM) and its application are presented. Three-dimensional refractive index structures can be fabricated inside glasses by focusing femtosecond laser pulses. When a three-dimensional structure is created, number of processing time is necessary. In addition, fast scanning cannot be applied to shorten the processing time, because long exposure time of laser pulses is necessary to avoid a formation of cracks in the photoexcited region. Therefore, fabrication efficiency is a critical problem. Our laser processing system with an SLM can improve the fabrication efficiency, because multiple light spots can be generated by modulating the spatial phase distribution of laser beam with an SLM. In this paper, we will present the principle of the laser machining system as well as the applications for parallel writing of 3D optical waveguides, diffractive gratings, and optical data storage.

The solar photovoltaic market is continuously growing utilizing boths crystalline silicon (c-Si) as well as thin film technologies. This growth is directly dependant on the manufacturing costs for solar cells. Factors for cost reduction are innovative ideas for an optimization of precision and throughput. Lasers are excellent tools to provide highly efficient processes with impressive accuracy. They need to be used in combination with fast and precise motion systems for a maximum gain in the manufacturing process, yielding best cost of ownership. In this article such an innovative solution is presented for laser scribing in thin film Si modules. A combination of a new glass substrate holding system combined with a fast and precise motion system is the foundation for a cost effective scribing machine. In addition, the advantages of fiber lasers in beam delivery and beam quality guarantee not only shorter setup and down times but also high resolution and reproducibility for the scribing processes P1, P2 and P3. The precision of the whole system allows to reduce the dead zone to a minimum and therefore to improve the efficiency of the modules.

Interfering ultra-short pulse laser processing can make nano-structures on metallic thin films. The unit nano-structures are nano-waterdrop, nanocrown, nanobump etc.. They change according to the character of target and the interference pattern. An interference pattern of four beams, diffracted by a transmission grating, is like a simple matrix. We generated arranged periodic structures different from the past experiments, by changing the configuration of four interfering beams. Parameters of an interference pattern are wavelength, correlation angle, difference of intensities and phase shift between the beams. As a result, complicated or duplicated structures can be generated.

We report on experiments using a near-infrared Ti:Sapphire laser system based on a 85 MHz, sub-15 fs resonator. In the negative photoresist SU-8 multiphoton polymerization of 3D structures resulted in a minimum line width of approximately 80 nm at aspect ratios in excess of 50:1. The second part of our contribution deals with sub-wavelength nanostructuring and laser-annealing of thin indium-tin-oxide (ITO) films. The ablation experiments allowed for the generation of cuts of sub-100 nm width in periodic and single cut arrangements. Annealing resulted in a different phase of ITO which is more resistive against etching in HCl at room temperature. The dependence of cuts on scan parameters that affect the ITO film properties was investigated.

We report on a refractive index modification (▵n) induced by femtosecond irradiation and evaluation of the profile for created lines inside the different types of optical glasses, i.e., silicate or borate glass containing the metal oxides such as BaO, TiO₂, or La₂O₃ and silica glass. The lines are fabricated by scanning a stage and focusing the femtosecond laser pulses, 800nm wavelength, a 250 kHz repetition rate and 200 fs pulse duration, from the Ti:sapphire regenerative amplifier system. The ▵n profiles of modification were obtained with Qualitative Phase Microscopy technique and presented systematically for a different input power and a variety of glasses. The ▵n profile changed with focusing condition using 10× (N.A.=0.3) or 40× (N.A.=0.85), and input power in a single glass. However, the ▵n and a trend of the sign was different depending on glass types. For example, silicate glass containing TiO₂, exhibited negative ▵n trend the ▵n became smaller in the modified region. Furthermore, the glass showed relatively large negative ▵n, < - 0.01 decrease of the ▵n, ▵n < -0.01, in the investigated power range. These results could be useful for a design or use of glasses for micro optics, such as grating, diffractive lens or lens array, produced by femtosecond laser fabrication.

In this paper, we report on a micro-cutting of carbon fiber reinforced plastics (CFRP) by nanosecond-pulsed laser ablation with a diode-pumped solid state UV laser (DPSS UV laser, λ= 355nm). A well-defined cutting of CFRP which were free of debris and thermal-damages around the grooves, were performed by the laser ablation with a multiple-scanpass irradiation method. CFRP is a high strength composite material with a lightweight, and is increasingly being used various applications. UV pulsed laser ablation is suitable for laser cutting process of CFRP materials, which drastically reduces a thermal damage at cut regions.

Silicone-coated polycarbonate (PC) through an acrylic primer was photochemically modified into silica (SiO₂) by 157 nm F₂ laser. The photomodified surface showed high scratch resistance comparable to the case in a bulk silica. Corresponding to the conversion of silicone into silica on PC, the photomodified surface was found to be shrunk, measured by a surface profilometer. For instance, the coated silicone on PC reduced the thickness of approximately 15 % when the F₂ laser modified silicone into silica 0.59 μin thickness. An excess irradiation of F₂ laser for the photochemical modification induced the degradation of acrylic primer underneath silicone.

A 157 nm F2 laser was used for the surface and interface modifications of Al thin films on silica glass substrate for fabricating a pattern of Al thin films. The F₂-laser irradiated surface swelled remarkably by inducing the strong oxidation reaction of Al thin films to form Al₂O₃ protective layer. High adhesion strength of 663 kgf/cm² between Al and silica glass was also obtained for the F₂-laser-irradiated sample, compared with the cases in the ArF-laser irradiated, fourth harmonic of Nd:YAG-laser irradiated and nonirradiated samples of 326, 19 and 16 kgf/cm², respectively. Thus, the F2- laser irradiated sample showed high abrasion resistance for embossing a fine pattern of Al thin films on silica glass. Mechanism of the F₂-laser-induced surface and interface modifications was discussed, comparing with the cases in the ArF laser and fourth harmonic of Nd:YAG laser.