Nd:YAG laser welding of high reflectivity metals is difficult because of the highly non-linear light-material interaction yielding a narrow process window and poor reliability. However, achieving high reliability is mandatory for applying this technique in industrial production lines. The welding control can be improved by real-time monitoring of the process evolution with sensors. Such sensor signals are particularly useful for weld classification and for laser power control in off-line or in closed-loop feedback configurations. The latter possibility is difficult to implement in pulsed lasers and requires a careful sensor choice. Here, we report on laser lap micro-spot welding of thin copper sheets using a pulsed Nd:YAG laser. The welding was performed under atmospheric conditions on pure, 50 μm thick, slightly oxidized copper sheets with pulse durations and energies of less than 8 ms and 8 J, respectively. The process was experimentally analyzed by detecting normal laser reflection, heat emission, and instantaneous laser power with high time resolution. The meaningful signal parameters have then been selected for a closed loop feedback control. The variance of top and bottom weld spot diameters could be reduced by more than a factor of 8 in the case of closed loop control.

Recent achievements in laser-induced surface patterning obtained in our group are summarized. Here, we have employed both a SNOM-type setup and two-dimensional lattices of SiO₂ microspheres formed by self-assembly processes. With the SNOM-type setup we have demonstrated nanoscale photochemical and photothermal etching, mainly of Si in Cl₂ atmosphere. With 2D lattices of microspheres a large number of single features can be generated by a single or a few laser shots. Among the examples presented is the surface patterning by ablation, etching, deposition, and surface modification.

As laser micromachining is applied to ever smaller structures and more complex materials, the demand for greater control of the laser energy budget, in space and time, grows commensurately. Here we describe materials modification using picosecond resonant laser excitation in the mid-infrared spectral region to create spatially and temporally dense vibrational, rather than electronic, excitation. Examples include ablation of fused silica and machining of crystalline quartz; deposition of functionalized polymers on microstructures, and laser-directed transfer of proteins and nucleotides from a matrix of water ice. The experiments demonstrate that high spatial and temporal density of vibrational excitation can be achieved by ultrafast resonant infrared excitation of selected vibrational modes of these materials. In some cases, resonant infrared materials modification is far more successful than techniques based on ultraviolet excimer lasers. The laser used for most of the experiments was a tunable, high pulse-repetition frequency free-electron laser. However, a comparison of polymer deposition using a conventional nanosecond laser at a wavelength of 2.94 μm shows that the possibility exists for transferring the concept to conventional table-top devices. Mechanistic considerations nevertheless suggest that utlrashort pulses are likely to be more useful than longer pulses for many applications. A figure of merit is proposed for self-consistent comparisons of processing efficiency among different lasers.

Laser Micro-Bending technology attracts attention as one of the laser processing technology promising from now on. It has the feature that does not contact and does not have the spring back that fabrication in high accuracy can be performed. In our company, Laser Micro-Bending technology development is tackled about ten years before, and the laser bending fabrication technology of a sheet metal and ceramic material has so far been established. It has utilized as rapid prototyping of the sheet metal. But, by re-examination of laser oscillation control etc., it finds out that it is the excellent processing method for manufacture of the high precision mechanism parts for magnetic disk drives. This report explains the technology and machines of the roll and pitch adjustment of a magnetic head suspension, and flatting or crowning of the air bearing surface of a magnetic head slider by using Laser Micro-Bending technology.

A method for surface metallization on transparent substrate with laser induced plasma deposition was described. A laser beam goes through the transparent substrate first and then irradiates on a metal target behind. For laser fluence above ablation threshold for the target, the generated plasma flies forward at a high speed to the substrate and induces metal materials deposition on its rear side surface and even doping into the substrate. The diffusion distribution of metallic particles was measured with Time of Flight Secondary Ion Mass Spectrometer (TOF-SIMS). Electrically conducting films are formed on the substrate with laser beam scanning. The near 1Ω/Square lower resistivity can be formed with precise control of the processing parameters. Laser fluence, pulse repetition rate and scanning speed, distance between the substrate and metal target and overlapping of the metal lines. This technology can be used to form electrodes, resistors, LCD or electronic circuits on the transparent substrates.

Ablation of mixture targets of perylenetetracarboxylic dianhydride (PTCDA) with cobalt powder is carried out using the third harmonic of a Nd:YAG laser to obtain thin films consisting of variety size of nanoparticles. FT-IR and Raman spectroscopic studies allow us to conclude that fragments without the anhydride groups of PTCDA and with better defined perylene skeleton are deposited on the substrates. Gradual increase of the electric conductivity with increasing substrate temperature during deposition suggests effective polymerization of the deposit to form polyperinaphthalene (PPN), one of low dimensional graphite family. Furthermore a Raman spectrum for each nanoparticle prepared by laser ablation at a fluence of 0.5 Jcm^-2pulse^-1 is successfully measured by the surface enhanced Raman spectroscopy (SERS) with a silicon tip for atomic force microscopy (AFM) coated with gold.

This paper introduces a novel laser chemical process for removing thin oxide films on low-carbon steel surfaces by combining laser-induced shock waves and chemical etching technique that is used in the conventional oxide-scale removal process. In the proposed process, a Q-switched Nd:YAG laser (wavelength 1064 nm, FWHM 6 ns) pulse is focused onto the liquid surface and subsequently induces optical breakdown in the acid solution, producing intense pressure waves. The pressure waves act as a non-contact oxide-film breaker and increases the removal rate. It has been demonstrated that the novel process leads to substantial enhancement of the oxide-film removal, compared with the conventional solvent-based cleaning technique. The removal rate has been measured quantitatively employing an optical microscope, a scanning electron microscope, and energy-dispersive X-ray analysis. Parametric study has been performed to reveal the effect of pressure pulse, laser pulse number, acid concentration, reaction time on the efficiency of scale removal. It is shown that the laser-assisted process can lower the acid concentration, with the cleaning efficiency unchanged or even improved. The results demonstrates a technical feasibility of utilizing the method for industrial applications that required enhanced scale-removal rate or reduced use of toxic chemicals.

Laser-induced chemical vapor deposition is applied to fabricate three-dimensional microstructures that have cross-sectional profiles other than simple combination of deposited fibers. To fabricate microstructures other than combined wire-frames, a thin layer of deposit in desired patterns is first written using laser-direct-write technique and on top of this layer a second layer is deposited to provide the third dimension normal to the surface. By depositing many layers, a full three-dimensional microstructure is fabricated. Optimum deposition conditions for direct writing of initial and subsequent layers with good surface quality and profile uniformity are determined. Using an argon ion laser and ethylene as the light source and reaction gas, respectively, fabrication of three-dimensional carbon microstructures with the proposed method is demonstrated.

ZnO thin films on (100) p-type Si and sapphire substrates have been deposited by pulsed laser deposition technique using Nd:YAG laser with a wavelength of 266 nm. The influence of the deposition parameters such as oxygen pressure, substrate temperature and laser energy density on the properties of the grown films, was studied. The experiments were performed for substrates temperature in the range of 200 - 500°C and oxygen pressure in the range of 100 to approximately 700 sccm. All the films grown in this experiment show strong c-axis orientation with (002) textured ZnO peak. With increasing substrate temperature, the full width at half maximum (FWHM) and surface roughness were descreased. In case of sapphire substrate, the intensity of PL spectra increased with increasing ambient oxygen flow rate. We investigated in the structural and morphological properties of ZnO thin films using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM).

The laser cleaning of the photoresist (PR) layer has been investigated as a function of laser energy density. The cleaning of the PR layer on silicon wafer was performed by a line beam of a KrF excimer laser in a cleanroom environment and then the applied energy density was 100 - 300 mJ/cm². The experimental results showed that the ablation rates of the PR are increased with increasing of laser energy density without silicon wafer damage. The ablation rates of PR were 0.09 μm/pulse for 100 mJ/cm², 0.15 μm/pulse for 200 mJ/cm² and 0.19 μm/pulse for 300 mJ/cm² with repetition rate of 30 Hz. The compositions of the PR covered wafers before and after laser irradiation were determined by Fourier transform infrared spectroscopy (FT-IR). The comparison of the cleaning results done in applying the laser cleaning to remove the PR and the metallic polymers resulting from reactive ion etching (RIE) was made before and after laser irradiation by scanning electron microscope (SEM). It is also shown that the PR and metallic polymer in the contact hole can be completely removed by the laser cleaning technique.

By irradiating a Nd:YAG (λ=266 and 532 nm, pulse) laser beam, we investigated the cleaning process of a photoresist particles on Si and ITO substrate. The influences of laser fluence, wavelength, and substrate properties on the laser cleaning performance were investigated. The removal rate for the particles of Si substrate was higher than that of ITO at the same laser fluence and pulses for a wavelength of 266 nm. Using 2nd harmonic Nd:YAG laser (λ = 532 nm), it was found to be inappropriate for the complete particle removal and ablation of photoresist film without substrate damage. Water-condensed particles are rarely cleaned even on the laser fluence of being capable of completely removing dried sample resulting from the increase of viscosity of the particles, the scattering, and the reflection of incident laser beam.

A carbon nitride film was synthesized by a pulsed laser deposition technique using an additional laser to irradiate the carbon plume. A highly oriented pyrolytic graphite target was ablated in a nitrogen atmosphere at a pressure of 0.1 torr. The optical emission intensities of ionic carbon and nitrogen from the carbon plume were increased by additional laser-irradiation. The ratio of N sp³-C bonds and nitrogen chemical content were also increased by the additional laser irradiation to the plume. The ratio of N sp³-C bonding and nitrogen content increased with additional laser irradiation at low but not high fluence from the ablating laser.

Laser surface treatment was used to modify the surface of silicon and PTFE (polytetrafluoroethylene). This method is in order to improve its wettability and adhesion characteristics. Using a 4th harmonic Nd:YAG pulse laser (λ = 266 nm, pulse), we determined the wettability and the adhesion characteristics of silicon and PTFE surfaces developed by the laser irradiation. Particularly, surface treatment of PTFE was only effective when the irradiated interface was in contact with the triethylamine photoreagent. We investigated laser surface treatment of materials by the surface energy modification. By using the sessile drop technique with distilled water, we determined that the wettability of silicon and PTFE after the irradiation showed a decrease in the contact angle and a change in the surface chemical composition. In case of the laser-treated materials surface, laser direct writing of copper lines was achieved through pyrolytic decomposition of copper formate films by using a focused argon ion laser beam (λ = 514.5 nm, cw) on silicon and PTFE substrates. The deposited patterns and the surface chemical compositions were measured by using energy dispersive X-ray, scanning electron microscopy, X-ray photoelectron spectroscopy, and surface profiler to examine cross section of the deposited copper lines.

Ultrashort laser pulse interaction with material involves a number of specialities as compared to longer irradiations. Applying femtosecond laser pulses, the fundamental physical processes such as excitation, melting and ablation are temporally separated, allowing a separate investigation of each of them. The irradiated material passes through highly non-equilibrium states of different kinds on different timescales after irradiation. Thus, the theoretical description of the investigated processes may differ strongly from the classical descriptions valid for equilibrium or steady-state conditions. On a femtosecond timescale we investigate the non-equilibrium of the laser-excited electron gas. With the help of a detailed microscopic approach we study the applicability of simplified macroscopic descriptions of laser absorption and free-electron excitation. We study different melting processes occurring on different timescales in the picosecond regime. The nature of the melting process depends on the laser and material parameters, respectively. Material removal, i.e. ablation, occurs on a pico- to nanosecond time scale, depending on excitation strength. We show theoretical and experimental investigations of the expansion dynamics of the excited material.

We have studied ablation plumes generated by femtosecond and picosecond-laser pulses using various optical methods for both single-pulse ablation as well as for drilling with up to 1 kHz repetition rate. Time-resolved shadow and resonance-absorption photographs visualize the plume- and vapor-expansion behavior in the nanosecond- and microsecond-time domains whereas the detection of Mie-scattered 308 nm-radiation allows to qualify the vapor movement and accumulation up to several milliseconds, i.e. well beyond the corresponding pulse-to-pulse separation at 1 kHz repetition rate.

The ablation process in sapphire and fused silica are studied with laser at 800 nm and 400 nm respectively. Comparing with the features of the ablated craters induced by different laser, we find that lasers with short wavelength and pulse duration can produce more exquisite ablation crater with small area and steep gradient. By means of determining the F_th with detection of the scattered light, the developments of the threshold fluence of dielectrics as a function of pulse duration are presented. While interpreting our results with existent model of optical breakdown, we discuss the excitation mechanism of conduction band electrons (CBE) in transparent dielectrics.

A new field in laser processing is opened by the method of modifying the optical properties, i.e. the refractive index, absorption- and scattering-coefficient, at minimal mechanical stress inside the material. Focusing ultra short laser pulses inside the transparent media allows to control and modify their optical properties. This is referred to as nik-engineering (TM), relating the technique to changes of the complex refractive index, i.e. (n+ik). Three dimensional patterns of the (n + ik) modifications can be achieved in the subsurface region even on a microscopic scale. New results in nik-engineering obtained in our application laboratory are presented using different optical materials. The results in laser nik-engineering of photo-chromic glass using ultra short laser pulses at a wavelength of 800 nm is presented. A model in respect to the relevant processes leading to the observed laser-induced modifications in the optical properties of photo-chromic glass is presented. We discuss the results and the commercial potential of nik-engineering.

We show that femtosecond laser enables us to produce true three-dimensional (3-D) microstructures embedded in a photosensitive glass, which has superior properties on transparency, hardness, chemical and thermal resistances. After exposure of the focused laser beam, the latent images are written. Modified regions are developed by a post baking process and then preferentially etched away in dilute solution of hydrofluoric (HF) acid solution in an ultrasonic bath at room temperature. The contrast ratio in etching selectivity is examined for different concentration of HF solution. Based on this result, a freely movable microplate which has a function of microvalve in the microreactor is fabricated inside the glass.

Three-dimensional (3D) microoptical components are embedded in a photosensitive glass Foturan by a femtosecond (fs) laser. This process includes mainly three steps: (1) direct writing of latent images in the sample by the tightly focused fs laser beam; (2) baking of the sample in a programmable furnace for the formation of modified regions; and (3) etching of the sample in a 10% diluted solution of hydrofluoric acid for the selective removal of the modified regions. After this process, hollow internal structures are formed, which act as a mirror and a beam splitter. Furthermore, we find that postannealing smoothes the surfaces of the fabricated hollow structures, resulting in the great improvement of the optical properties. We examine the optical properties of the structured components using a He-Ne laser beam, and measure the optical losses at 1.55 μm wavelength.

Laser processing of glass components is of significant commercial interest for the optoelectronics and telecommunications industries. In this paper, we present laser processing techniques using microsecond, nanosecond, and femtosecond lasers for machining of glass. Surface structures, mainly groove geometries, are generated with a diode-pumped solid-state nanosecond pulsed UV laser operating at 266 nm, a Q-switched CO₂ laser operating at 9.25 μm, a CO₂ laser operating at 10.6 μm and the femtosecond pulsed laser operating at 800 nm. Grooves are cross-sectioned and viewed with a focused ion beam (FIB) microscope. The resultant material structures are examined with respect to the differences in time scale and the appropriateness of each laser type for particular processes.

F₂-laser ablation at 157 nm was used for generating sub-micron surface relief structures on fused silica to define binary diffractive phase elements (DPE). A pattern array of 128 x 128 pixels was excised using the F₂ laser in combination with a high resolution processing system comprising of CaF₂ beam-homogenization optics and a high-resolution Schwarzschild reflective objective. A square projection mask provided precise excisions in less than 10 x 10 μm² spots, having sub-μm depths that were controlled by the laser fluence and the number of laser pulses to provide for the required phase delay between ablated and non-ablated pixels. Thus a diffractive phase element (DPE) optimized for first order in the UV spectral range was made. A four-level DPE design computed by the Iterative Fourier Transform Algorithm (IFTA) will be described for generating an arbitrary irradiation pattern without the point symmetry of a two level design.

A novel approach for the fabrication of micropatterns where dye molecules can be site-selectively desposited is described. The micropatterns were fabricated on the surface of fused silica plates using the technique of laser-induced backside wet etching (LIBWE). Prior to the LIBWE process, the surface properties of the fused silica plates were modified with self-assembling trimethoxysilanes bearing functional moieties. On the non-irradiated areas, the self-assembled monolayers (SAMs) survived the LIBWE process, and the remaining SAM acted as a template for the subsequent dye deposition either with chemical bonding or physical adsorption. Site-selective dye deposition was visualized with fluorescence microscopic observation. These results are applicable for micro-fluidic reactors and chemical sensors.

It was found that titanium ions in glasses are effective to reduce the ablation threshold in the UV laser irradiation. The glasses containing titanium ions showed one order smaller thresholds compared with other commercial glasses used for optics or windows. The lowest threshold around 200 mJcm^-2 was obtained in 266-nm irradiation from a forth harmonics of Nd:YAG laser. The ablation threshold decreases with increasing the titanium concentration in the glass. On the other hand, the ablation rate shows the maximum value at the molar ratio of titanium oxide around 10 - 20 mol% in the glass composition. A 4 x 4 planer micro-hole array (PMH) consist of the titanium containing glasses was successfully fabricated with a KrF excimer laser (248 nm). Because of the good machinability effective to prevent cracking and chipping during the laser machining, the PMH showed good uniformity of hole diameter (average: 129.9 μm) with σ = 0.8 μm.

By laser-micromachining from the rear surface that is in contact with distilled water, we can directly produce Three-dimensional micro-holes in silica glass. The micro-holes have the constant diameters of several microns and the high aspect ratios. In this paper, we present the morphological characteristics of the micro-hole. Femtosecond laser pulses (130-fs, 800 nm, 1-kHz) generated from an amplified Ti:sapphire laser were first focused onto the rear surface of the silica glass with the thickness of 1 mm by a 0.55-numerical aperture microscope objective. After 48 sequential pulses were launched into the sample, we moved the focal spot by a step of 1 micron toward the front surface. We fabricated micro-holes with the diameter of 4 - 8 microns by repeating the irradiation and the movement. We observed the morphology of the hole and the debris generated by the laser ablation. We also analyzed the capillary phenomenon in the dead-end micro-holes. We found two phases in the rising of the distilled water: the first phase occurred very fast within 0.1s and second phase was slow. This result agrees with the previous result [N.P. Migoun, et al., Proc. 15^th WCNDT, Roma(2000)] that used a glass capillary tube.

Precise laser microfabrication of glass is a high challenge task due to the stress-induced microcracks generated during laser ablation. In this paper, the results of high quality glass microfabrication by low energy Nd:YAG laser (355 nm, 30 ns) ablation and pocket scanning technique are presented. The pocket scanning is to scan the laser beam along parallel overlapped paths with the last path along the structure edge, while the conventional direct scanning is to scan the beam just along the structure edge. It is found that the cracks formed around the edges by pocket scanning are reduced significantly compared to that by direct scanning. Minimum crack sizes of less than 10 μm have been obtained at optimized parameters. The ablation depth is also enhanced greatly by pocket scanning to increase almost linearly with the laser fluence and scanning loop. There are no limitations of saturation as that observed in the cases of direct scanning.

Laser amorphization of glass-ceramics (LAGC) is investigated by optical pyrometry and video recording. Due to this new knowledge, the mechanism of local LAGC is made clear as a phenomenon leaded by thermal kinetic. The required power density and temporal range of CO₂-laser irrdiation for amorphization of a typical glass-ceramic (GC) α-TiO₂ • 2MgO • 2Al₂O₃ • 5SiO₂ is defined. It is demonstrated that a wide range of miniature optical components such as lenses, lenslet arrays, waveguides, geodesic (plane) lenses, etc... can be fabricated by LAGC.

Microparts with a structural resolution of <30μm and aspect ratios of >12 have been generated by selective laser sintering. The technique includes sintering under conditions of vacuum or reduced shield gas pressures. In a novel set-up the material is processed by a Q-switched 1064nm Nd-YAG laser after a special raking procedure. The procedure allows the work pieces to be generated from powders of high melting metals like tungsten as well as lower melting metals like aluminium and copper. Contingent on the parameters, the generated bodies are either firmly attached to the substrate or can be dissevered by a non-destructive method.

We have used KrF excimer laser ablation in the fabrication of a novel MEMS power conversion device based on an axial-flow turbine with an integral axial-flux electromagnetic generator. The device has a sandwich structure, comprising a pair of silicon stators either side of an SU8 polymer rotor. The curved turbine rotor blades were fabricated by projection ablation of SU8 parts performed by conventional UV lithography. A variable aperture mask, implemented by stepping a moving aperture in front of a fixed one, was used to achieve the desired spatial variation in the ablated depth. An automatic process was set up on a commercial laser workstation, with the laser firing and mask motion being controlled by computer. High quality SU8 rotor parts with diameters of 13 mm and depths of 1 mm were produced at a fluence of 0.7 J/cm², corresponding to a material removal rate of approximately 0.3 μm per pulse. A similar approach was used to form SU8 guide vane inserts for the stators.

Modern metal forming technologies enable the mass-production of smallest parts for micro-technical applications. The future trend is to manufacture more complex parts at a high level of economic efficiency and precision. A common method to enhance the geometrical complexity of micro parts is the preheating of the workpiece. Conventional preheating processes are time cosuming, decrease the productivity and heat the complete workpiece, which can be disadvantageous in processes like deep-drawing. By a direct heating with laser radiation the temperature of local regions of the work piece can be increased quickly and the achievable process limits can be extended. Transparent tool parts made of sapphire permit the guidance of the laser radiation directly onto the workpiece within the closed tool during the process. This means no further preheating step and the avoidance of an extended total process time. In this paper applications of this technology in deep-drawing and can-extrusion processes as well as possibilities for theoretical predictions of dominating phenomena are discussed.

Micro technology is an application field, in which laser-based processes show a particularly high growth potential. New developments within the range of laser sources promote the laser application likewise, as the multiplicity of today already successfully realized applications. These encourage users ever more to focus on the tool called laser. With this contribution one tries to give an overview over developments and trends in the most important branches of laser beam micromachining. In detail semiconductor manufacturing, interconnect and micro mechanics are addressed. The contribution neither raises a claim on completeness, nor is to be given an absolutely measurable evaluation of the innovation value of interesting new developments. The goal of this contribution is to be a basis for a fruitful discussion between laser researchers, developers, users and manufacturers by supplying with information about activities in the field of micro technology.

From the general trend towards higher functional integration and miniaturization results an increasing demand for metallic parts of smallest dimensions. Metal forming processes are best suited for these applications in terms of productivity and accuracy. But problems arise from the so called "size effects" related to these small dimensions, e.g. the influence of the microstructure becomes an important aspect to consider. An approach to these problems is the laser-assistance of the microforming process. Laser light is used to increase the temperature of the material during forming, reducing the flow stress and increasing the ductility. By controlling the temperature in the workpiece via laser radiation the microstructure can be modified by inducing recrystallization and thus increasing the formability in the required area of the part. This can also be verified by FEM simulations of the forming process. To enable the transmittance of laser light into the workpiece, sapphire tools are used. The machining of these tools has been carried out by laser ablation with wavelengths in the UV range, e.g. with excimer lasers. Experimental investigations have shown that the manufacturing of sapphire tools and their use in laser-assisted microforming processes is a suitable method for the mass production of microparts.

High-precision adjustment of smallest optical and electronic components is increasingly recognized as one of the key issues facing micromachining technology. As even narrow production tolerances for all individual parts are often not sufficient to match the tightly specified positioning accuracies of the complete assembly, in situ adjustment techniques are gaining more and more attention. Together with research partners from industry and science, the BLZ is developing a contact-free, laser-based adjustment method which allows high-accuracy adjustment of components mounted on specifically designed actuators. The underlying mechanisms do not depend on thermal effects but on selective laser ablation of prestressed layers of actuator substrate. This way, slightest deformations or modifications of particular mechanical properties can be initiated. The method promises to be more accurate and less time consuming than thermally induced laser bending.

A novel device suited for the generation of sintered microparts of metal and ceramics, for reaction sintering and for CVD has been developed and successfully tested. With the production of a functional component it has evidenced professional performance. The set-up is vacuum tight; unstable substances can be processed under various shield gases and pressures; it is equipped with a device suited to rake thin layers of fine powders as well as slurries. Sub micrometer powder can be processed in steps of 1 μm thick sintered layers. In combination with a proprietary sintering regime, micro parts with a structural resolution of <30μm, and aspect ratios of >10 have been achieved.

This paper describes the fabrication of micro-channels in resin for micro-fluidic devices such as the μ-TAS (Micro Total Analysis System) by a UV laser ablation. Numbers of heat-hardening resin-films are piled up a soda glass. A laser fabricates a part of the channel at the each film every lamination, and then 3-D confluence channels are fabricated. The channel sizes are widths of 20 - 150 μm and depths of 20 - 30 μm. The through holes are made in the laminate film by the laser. Inlet pipe for a micro-pump are inserted into the hole. Deionized water is injected into the channels with a microinjection pump. This flow rate is 5 μL/min. There is no damage to the channel, inlet, and outlet.

Silica glass is an important material in optics and optoelectronics because of its outstanding properties, such as transparence in a wide wavelength range, strong damage resistance for laser irradiation, and high chemical stability. In order to develop simpler processes of micro-fabricating silica glass using a pulsed laser, we have investigated a one-step method to microfabricate a silica glass plate using laser-induced backside wet etching (LIBWE) upon irradiation with a ns-pulsed excimer laser. Our idea of LIBWE is based on the deposition of laser energy on the surface of silica glass using ablation of a dye solution. When the dye solution was ablated upon the laser irradiation, the etching of a surface layer was performed on the silica glass. We have succeeded in the micro-fabrication of such transparent materials as silica glass, quartz, calcium fluoride, sapphire and fluorocarbon resin. The advantages of our LIBWE method are as follows, (1) a lwo laser fluence and constant etch rate, (2) microfabrication without debris and cracks formation, (3) large area irradiation with an excimer laser beam through a mask projection, (4) simple pre/post-treatment on target substrates. This is a one-step process simpler method at ambient pressure, which would be used for mass production.

An overview on the rear side ablation process and its characteristic mechanisms is presented. Starting with a description of the commonly used front side ablation and definitions of the ablation efficiency, we give results from our investigations of the model system black paint on floatglass, processed with q-switched Nd:YAG laser, operating with pulse durations of 360 ns and 8 ns at a wavelength of 1064 nm. In addition we present results from various other samples and laser sources such as Excimer laser. The experiments confirm that the efficiency for the rear side ablation process is up to two magnitudes higher than that for front side ablation and that the process is more efficient for the shorter pulse duration. Some quality aspects are discussed, that have to be taken into account, when rear side ablating. We present a first general model to explain the surprisingly high difference in the ablation efficiency and the fact, that the rear side ablation efficiency increases with increasing layer thickness. We address the initial thermal ablation step being threshold-determining and the final photomechanical step being efficiency-determining. Finally, we give an outlook to next approaches.

In recent years industry has shown a growing interest in the field of micro-structuring of surfaces on macroscopic workpieces. Several applications to improve the tribological properties of surfaces are known as well as various techniques for printing and embossing. First industrial applications use pulse durations of nanoseconds or longer. However, the quality of the resulting structures is limited due to the formation of recast that has to be removed by additional post-processing. Experimental results have shown that it is possible to avoid recast formation by shortening the pulse duration into the femtosecond regime when low energy density values are used. Detrimental is the fact that process speed with available laser systems is low compared to nanosecond processing. This contribution will show and discuss results in the field of surface structuring of metals with laserpulses in the range from nanoseconds to femtoseconds. The final decision between nanoseconds and femtoseconds has to be made for each specific application.

The pulse width -- pulse energy relationship of a solid-state laser can reduce the accuracy of micro machined features. Our goal is to control a depth of a laser mark with an accuracy of 0.1 μm and reduce the line width below the spot diameter. Reaching this depth and width in a stable and industrial viable laser process would not have been possible without the additional control generated by the beam attenuator.

In the production of micro devices for applications in chemistry, biotechnology and medical technologies surface properties become more and more important. The microscale topography and surface chemistry have influence on wetting properties and cell behavior. Therefore the design of material surface determines the success of artificial devices in contact with biological systems. For applications in the field of medical implants laser technologies have been developed for micro structuring of polymers to modify the surface properties with respect to wettability and controlled cell growth. The technology is based on excimer laser treatment of polymer surfaces using laser wavelength 193 nm (ArF) with different fluences and cumulated energies. Depending on the processing parameters and examined polymers either hydrophobic or hydrophilic surfaces can be increased. The water contact angle of polydimethylsiloxane (PDMS) for example can be increased from 113° to approx. 150° so that the surface exhibits the so called lotus effect. The laser generated micro patterns reveal influence on cell density and cell distribution which can be used for cell guidance. Results for cell growing experiments are shown for different polymers.

Direct laser recording of two-dimensional and three-dimensional periodic structures in a glass containing nanocrystalline Ag clusters is demonstrated. The Ag-doped glasses were irradiated by the third harmonic of a Nd:YAG laser (354 nm) with pulse duration of 7 ns and 10 Hz repetition rate, and fluences which varied from 0.2 fto 1.2 J/cm². Four intersecting beams of equal intensity were used to create an intensity-modulated pattern at the glass surface and the fifth beam was used to obtain intensity modulation in the bulk. The resultant gratings written in the glass as well as the kinetics of the laser-induced evolution of the Ag clusters were studied by AFM and optical microscopy. Under illumination the nanocrystals move rapidly toward the surface and towards one another, agglomerate and coalesce. The mechanisms and kinetics of light induced mass transfer occurring during recording are analyzed. The kinetics of cluster motion is estimated.

In this treatment method laser radiation, which is guided from a coaxially expanding liquid jet-stream, locally initiates a thermochemical etching reaction on a metal surface, which leads to selective material removal at high resolution and quality of the treated surface as well as low thermal influence on the workpiece. Electrochemical investigations were performed under focused laser irradiation using a cw-Nd:YAG laser with a maximum power of 15 W and a simultaneous impact of the liquid jet-stream consisting of phosphoric acid with a maximum flow rate of 20 m/s. The time resolved measurements of the electrical potential difference against an electrochemical reference electrode were correlated with the specific processing parameters and corresponding etch rates to identify processing conditions for temporally stable and enhanced chemical etching reactions. Applications of laser-induced liquid-phase jet-chemical etching in the field of sensor technology, micromechanics and micrmoulding technology are presented. This includes the microstructuring of thin film systems, cutting of foils of shape memory alloys or the generation of structures with defined shape in bulk material.

The precision machining of glass by laser ablation has been expanded with the short wavelength of the 157 nm of the F2 excimer laser. The high absorption of this wavelength in any optical glass, especially in UV-grade fused silica, offers a new approach to generate high quality surfaces, addressing also micro-optical components. In this paper, the machining of basic diffractive and refractive optical components and the required machining and process technology is presented. Applications that are addressed are cylindrical and rotational symmetrical micro lenses and diffractive optics like phase transmission grating and diffractive optical elements (DOEs). These optical surfaces have been machined into bulk material as well as on fiber end surfaces, to achieve compact (electro) -- optical elements with high functionality and packaging density. The short wavelength of 157 nm used in the investigations require either vacuum or high purity inert gas environments. The influence of different ambient conditions is presented.

This paper describes a new approach for micromachining using optical radiation pressure, which can not only trap and manipulate, but also rotate a dielectric particle with micrometer size. In order to verify the feasibility of our proposed micromachining, we fabricated a shuttlecock optical rotator as a rotational micromachining tool from a silica particle (5μm in diameter) by focused ion beam (FIB). Fundamental experiments were performed about the influence of focus point and laser power on the rotational properties of the machining tool. Furthermore, by traversing the rotating tool over the silicon wafer surface, it was found that the micro groove with several nm in depth could be generated.

A theoretical model for laser ablation of polymers is developed. The model includes the description of radiation transport processes for the two-photon stepwise absorption of chromophores. This processes results in a nonlinear loss for the laser fluence, which can be expressed in term of the effective absorption coefficient α_eff. The behavior of α_eff as a function of incident fluence, applied wavelength, linear, excited state and plume absorption cross sections will be analyzed. This model accounts for a wide variety of observations such as fluence thresholds, wavelength and fluence dependent etch rates. An expression for the etch depth as a function of incident fluence is derived. It will be shown that the theoretical analysis describes accurately the trend of the noval photopolymers ablation results, which are recently reported in literature.

Multiple pulse laser ablation of polymer is performed with DPSS (Diode Pumped Solid State) 3rd harmonic Nd:YVO₄ laser (355 nm) in order to fabricate three-dimensional micro components. Here we considered mechanistic aspects of the interaction between UV laser and polymer to obtain optimum process conditions for maskless photomachining using DPSSL. The photo-physical and photochemical parameters such as laser wavelength and optical characteristics of polymers are investigated by experiments to reduce plume effect, which induce the re-deposited debris on the surface of substrate. In this study, LDST (laser direct sculpting technique) are developed to gain various three-dimensional shape with size less than 500 micrometer. Main process sequences are from rapid prototyping technology such as CAD/CAM modeling of products, machining path generation, layer-by-layer machining, and so on. This method can be applied to manufacture the prototype of micro device and the polymer mould for mass production without expensive mask fabrication.

Our previous paper reported on pulsed CO₂ laser induced periodic microstructures on the silicon substrates, which are coated with a thin material layer at the bottom surface to promote optical absorption. Our further study shows that two sets of parallel fringes generated at right angles can overlap and produce crossed-grid patterns when the laser pulse energy just crosses the thershold required for fringe formation. The fringe period is of sub-wavelength scale and the crossed-grid pattern is of grid size 2 μm by 2 μm. The fringes are considered to be due to the laser induced periodic surface structure (LIPSS) effect. The crossed-grid patterns are only possible when thermal bumps due to the thermal capillary wave effect are minimized, and they become re-writable at higher pulse energies.

The availability of extreme ultraviolet (EUV) light sources, measurement tools and integrated test systems is of major importance for the development of EUV lithography for use in large volume chip production starting in 2009. The EUV steppers will require an output power from the EUV source of 115 W at 13.5 nm for economic chip production. In addition, the EUV source must achieve rigorous specifications for debris emission and source facing condenser optics lifetime, source component lifetime, repetition rate, pulse-energy stability, plasma size and spatial emission stability, and spectral purity as a result of lithography system design constraints. Significant progress has been made in the development of laser produced plasma and gas discharge produced plasma based EUV sources as well as metrology tools to measure EUV radiation characteristics. As of today, the first EUV sources and measurement equipment are available to be used for EUV system, mask, optics and component as well as lithography process development. With the commercial availability of EUV-plasma sources other applications using short wavelength, XUV-radiation will be feasible in a laboratory environment. Some examples of XUV applications are discussed.

A compact extreme ultraviolet (EUV) source for metrology is developed. This source is based on an extension of conventional x-ray tube technology into the EUV spectral range. As in an ordinary x-ray tube, electrons are generated by a filament, accelerated in a high-voltage electric field toward an anode, and focused onto a solid target. In this "EUV tube" silicon targets are used to generate radiation at 13.5 nm. Absolute conversion efficiencies from electrons into EUV photons are measured. Illustrations of spectral and spatial properties are given and investigations of the long-term stability of the EUV emission are performed. Possibilities for a power scaling into the milliwatt range are discussed.

The Extreme Ultraviolet Lithography System Development Association (EUVA) started an extreme ultraviolet (EUV) light source development project for EUV lithography. Both, laser produced plasma (LPP) sources and gas discharge produced plasma (DPP) sources are developed in this project. The development status of the laser produced plasma EUV light source is reported including the xenon jet system and the 500-W laser system. Laser parameter optimization, for example laser pulse energy, pulse width and laser spot size, is ongoing to improve the conversion efficiency and EUV output power. A maxium conversion efficiency of 0.53% is obtained with a 50-μm diameter target. The EUV output stability is analyzed based on spatial fluctuations of the Xe jet and the laser beam. In addition, a Xe ion exposure measurement has been started to investigate the collector mirror damage mechanism.

Various solid materials have been irradiated with laser intensities ranging from 10¹¹ to 10¹⁶ W/cm² and the plasma emission has been measured between 7 nm and 18 nm. A chirped pulse amplified Ti:Sapphire laser oscillating at 790 nm with either 100 fs or 300 ps pulse duration and a Nd:YAG laser oscillating at 1064 nm with 10 ns pulse duration (fwhm) have been used. Tin, aluminum and copper have been chosen as targets. It has been found that the plasma emission was strongest for the 300 ps laser pulse irradiation. This might be due to the additional laser plasma heating during plasma formation.

Extreme-ultraviolet (EUV) lithography is most promising technology for 50 nm technology node which will be used from around the year 2007. There are many issues for realizing EUV lithography, such as developing optical components and radiation sources and one of the most important challenging tasks is to develop an EUV light source. Various technical concepts for realizing high power sources for EUV lithography are under investigation worldwide. Laser produced plasmas (LPP) and discharge produced plasmas (DPP) are the most promising schemes. In general, DPP methods are of special interest, because their prospected costs for the demanded throughput is expected to be much lower than those of LPPs. However, the discharge plasmas are of high risk, because many crucial problems have to be solved before reaching the required power levels. In this work, a high repetitive, compact and low-debris Xe-filled capillary Z-pinch discharge system has been designed and fabricated as an EUV source. We devised an electrode configuration compatible with the system and applied a magnetic switch and a static induction (SI) thyristor stack as a main switch of power modulator.

In order to investigate the applicability of laser micro welding to the fabrication of medical devices, Ti-Ni based shape memory alloy biomaterials wires were micro spot melted by using YAG laser. By the optimization of laser conditions such as laser power or pulse duration, sound spot melted wires free from any defects were prepared and the width of the melted metal was reduced to about 0.2 mm for the 0.15 mm diameter wires. Compared with the SUS304 wires, melting of shape memory alloy wires needed more precise control of laser conditions although it needed smaller power input. Melted metal exhibited a rapidly quenched microstructure. The spot melted wires showed 70% of tensile strength and almost the same super-elastic behavior compared with base materials. Besides, it was confirmed by immersion test and by measurement of anodic polarization curve that NT-E4 wires still retain a sound corrosion resistance in a quasi biological environment by laser spot melting. Crosswise or parallel joints was also successfully prepared by laser spot welding of wires, suggesting the laser micro welding is applicable to the fabrication of biomedical devices.

Recently, industrial products parts and components are being made smaller to reduce energy consumption and save space, creating a growing need for micro-welding of thin foil less than 100 mm thick. For this purpose, laser processing is expected to be the method of choice because it allows more precise heat control compared wih arc and plasma processing. In this report, the practicability of welding thin stainless steel foil with a direct diode laser system was investigated. The elliptically shaped laser beam of the direct diode laser enabled successful butt-welding of thin stainless steel foil 100 μm and less in thickness. Foil as thin as 50 μm could be successfully welded with a narrow bead width of 150 μm at a high speed of 18.0m/min. No spatter or plasma plume was observed when welding without an assist gas. The tensile strength of the weld bead was nearly the same as that of the base material.

Implantable microsystems currently under development have the potential to significantly impact the future treatment of disease. Functions of such implants will include localized sensing of temperature and pressure, electrical stimulation of neural tissue and the delivery of drugs. The devices are designed to be long-term implants that are remotely powered and controlled for many applications. The development of new, biocompatible materials and manufacturing processes that ensure long-lasting functionality and reliability are critical challenges. Important factors in the assembly of such systems are the small size of the features, the heat sensitivity of integrated electronics and media, the precision alignment required to hold small tolerances, and the type of materials and material combinations to be hermetically sealed. Laser micromachining has emerged as a compelling solution to address these manufacturing challenges. This paper will describe the latest achievements in microjoining of metallic and non-metallic materials. The focus is on glass, metal and polymers that have been joined using CO₂, Nd:YAG and diode lasers. Results in joining similar and dissimilar materials in different joint configurations are presented, as well as requirements for sample preparation and fixturing. The potential for applications in the biomedical sector will be demonstrated.

Microwelding thin stainless steel foil with thickness between 10 and 100 μm was studied by using a single-mode Yb-fiber laser with a CW maximum output of 40W, of which focused spot size was approximately 10 μm in diameter providing maximum power density of 10⁸W/cm². The energy coupled to the specimen was estimated by the thermal conduction analysis and the laser energy passing through the metal foil measured by an integrating sphere. The critical power density for keyhole welding was approximately 2.5 * 10⁷W/cm², which was at least 2 orders larger higher than the conventional macrowelding. Keyhole welding was maintained up to at least 1 m/s without weld defects such as humping and undercut, because the flow velocity of molten metal around the keyhole is lowed so that instability of the melt flow behind the keyhole can be suppressed in microwelding at high welding speeds. Sound lap welding of thin foils of the thickness of 10 μm to 30 μm was demonstrated even with gaps between the foils.

The combination of dissimilar materials like brass and stainless steel is often needed in watch movements due to tribologic aspects. For mass production in automotive applications, a joining technique for alloyed copper with alloyed steel is needed. Laser beam micro welding offers an alternative to conventional joining techniques like press fit or soldering. Depending on the joining geometry, two different welding techniques are investigated: seam and spot welding. High strength and reproducibility are the main objective of joining dissimilar metals. Cracks and spillings are affected by the metallic continuity and should be avoided. Lap- and T-joints can be produced by the SHADOW-Welding technique. The length of the continuous welding seams are up to 15.7 mm at a feed rate of up to 60 m/min with a pulsed laser source. The weld width attained ranges from 50 to 250 μm and a weld depth from 20 to 150 μm. This low energy joining process with minimized heat input results in low distortion of the parts joined. Applying spot welding, the pulse forming capability is needed especially for highly reflective metals like copper. The welded joints have a higher strength than the basic material.

The most widely used basic building block for high power diode lasers systems is a 19 emitter diode laser bar. For materials processing tasks, these may be used as single bars, can be built into vertical stacks or may be fiber coupled. For certain applications a line of light is preferred to a round beam and hence the use of fiber optic delivery may not be necessary. Straightforward optics can be used to convert the divergent output from this diode bar into a rectangle of line of focused light but the uniformity of the beam within this rectangle is a major problem. When diode bars are stacked vertically, this problem becomes 2 dimensional for anything other than a tightly focused beam. In particular, when a single bar line source is used to cover a large surface area by motion normal to the long axis of the beam, this non-uniformity creates fluctuations in intensity due to the separation between the individual emitters on the bar. This in turn causes processing problems when a laser line is used to seal multiple micro-fluidic devices. This work reports the use of a novel technique combined with conventional fiber delivered sources and novel laser line sources to tackle this problem.

Laser micro welding has become a standard manufacturing technique, particularly in industry sectors, such as automotive and aerospace electronics or medical devices, where the requirements for strength, miniaturization and temperature resistance are constantly rising. So far the use of laser micro welding is limited due to the fluctuation of the quality of the welded joints, because the welding results for material with high optical reflection and thermal conductivity, such as copper and copper alloys, depend very strongly on the condition of the material surface. This paper presents investigations on the use of a laser pre-pulse in spot welding of electronic materials with Nd:YAG laser. In order to achieve reproducible joining results two strategies are followed-up. The first one utilizes a reflection-based process control for measuring the reflection during the short pre-pulse. The intensity of the reflected light is used to calculate an appropriated welding pulse power, which corresponds to the measured relative absorption. Adjustment of laser parameters according to the condition of the surface is done in real time before laser main pulse. A second possibility for the stabilization of copper welding is the employment of a short and powerful laser pre-pulse before laser main pulse. This pre-pulse affects the workpiece surface and creates more reproducible absorption conditions for the main pulse, independent from the initial situation on material surface.

It has been proved that NiTi shape memory alloy thin film is the best one for micro actuators as compared with the others, e.g., electrostatic, electromagnetic and piezoelectric thin films. If the deposition of NiTi thin films on silicon wafers is carried out at room temperature, the resultant thin films are normally amorphous without shape memory. Subsequent annealing in a high vacuum chamber is required for re-crystallization. In this paper, we present an alternative annealing approach, namely by CO₂ laser. After laser annealing, optical microscope, X-ray diffraction (XRD) and atomic force microscope (AFM) were applied to characterize the NiTi thin films. Strong austenite/martensite lattice structures were observed by XRD. The relationship between the surface roughness of the annealed NiTi thin film and temperature was obtained using AFM. The results indicate that the CO₂ laser annealed NiTi thin films are with shape memory.

Pulsed laser ablation is important in a variety of engineering applications involving precise removal of materials in laser micromachining and laser treatment of bio-materials. Particularly, detailed numerical simulation of complex laser ablation phenomena in air, taking the interaction between ablation plume and air into account, is required for many practical applications. In this paper, high-power pulsed laser ablation under atmospheric pressure is studied with emphasis on the vaporization model, especially recondensation ratio over the Knudsen layer. Furthermore, parametric studies are carried out to analyze the effect of laser fluence and background pressure on surface ablation and the dynamics of ablation plume. In the numerical calculation, the temperature, pressure, density, and vaporization flux on a solid substrate are obtained by a heat-transfer computation code based on the enthalpy method. The plume dynamics is calculated considering the effect of mass diffusion into the ambient air and plasma shielding. To verify the computation results, experiments for measuring the propagation of a laser induced shock wave are conducted as well.

A high power laser diode system for welding is widely known. However, the reliability and the reasonability are required by an industrial market. Reliability, especially lifetime, mainly depends on the temperature of laser diode (LD) and it might be rise if LD would receive reflection from welding point. This paper conducted the measurement of the reflection during welding by applying 1/4 wavelength plate and PBS. Results indicated the reflection during welding was inevitable. We developed a prototype high power laser diode system, which equipped an anti-reflection unit, to improve the reliability. The system traveled 3m/min and its bead width was 1.2 mm for 1.5 mm Al (A5052) under the spot size 2.7 x 0.6 mm FWHM. Additionally, we started to develop fast and slow collimation lenses for LD to realize a reasonale price for system The brief evaluation of fast collimation lenses was also reported.

The mechanism for removal of a single-crystal silicon in laser drilling using a KrF excimer laser was investigated. A time-resolved interference analysis was carried out to measure the surface profile of the Si during and after laser irradiation at a laser fluence in the range of 4 - 11 J/cm². The 2nd harmonic output of a Q-switched Nd:YAG laser, the pulse duration of which was 10 ns, was used as the light source of the interferometer. The volume change of Si by melting and thermal expansion was directly observed. The formation and the growth of a sharp projection surrounding the laser-irradiated area was also observed during and after irradiation.

Holes and grooves of a few tens of micrometers have been fabricated on glass plates by femtosecond laser pulses in air. Shapes and surface morphology of the fabricated structures have been studied in detail by making their replicas. Details of the internal shape of the strictures formed have been studied by making replicas of them. Development of the shape of drilled hole with the increase in irradiated pulse number shows some distinguishable stages. Smaller number of pulses make channel at the center of rather flat bottom. With the increase of pulse number, the channel changed into conical, funnel-like shape as the depth increased. Shape of the groove depends on the scanning speed, i.e., number of irradiated pulses on the same position. The groove show little cracking or beaking with clear edges. Some amount of debris deposited along the groove but these debris were easily removed by smear. Inner surface of the groove has coarser morphology than that of the hole. Depth of the grove was shallower than that of the hole, even though the number of irradiated pulse was estimated to be equal.

Creating individual complex three dimensional structures in HIP-zirconia by conventional mechanical machining, e.g. milling, is time consuming and subject to significant loss in bending strength due to microcracking during the milling process. Utilizing ultra-short laser pulses, individual complex three dimensional microstructures can be created very precisely without significant damage to the structure. This advantage is used to process HIP-zirconia in order to create dental restorations. To evaluate efficiency and quality, different laser parameters such as pulse duration, pulse energy and ablation strategies were studied. The maximum ablation rate was found at 400 fs.

Ultrashort laser pulses appear very promising for material removal with highest precision. However, our investigations show several unexpected quality problems such as formation of recast, ripples, and irregular hole shapes even in the femtosecond-pulse regime. In this contribution influences on drilling efficiency and hole quality by several process parameters such as repetition rate and pulse duration will be presented and discussed. Furthermore different processing techniques to increase the drilling velocity will be shown. A suitable device for that purpose is a trepanning optic which was specially designed for the drilling of injection nozzles. By a variable angle of beam incidence it allows to produce holes with a well-defined conicity in combination with the high precision achieved by helical drilling.

Due to the rapid development of ultrashort lasers, quality of the machining is of prime interest for several applications. For instance deep marking of various materials. In this case, the depth can be controlled, knowing the ablation rate for the corresponding material. The evolution of ablation rates of Al, Cu and Ni are given in relation to the energy density. In metals the effect of thermal diffusion has to be taken into account to control collateral effects and especially the heat affected zone.

Surface replica films taken from fs-laser machined silicon wafers coated with a 20 nm thick layer of nickel are analyzed in an environmental scanning electron microscope. Electron-probe microanalysis on the replica film is used to assess the spatial distribution and elemental composition of debris.

Mask patterns in the shape of lines were transferred on gold thin films by laser ablation using femtosecond laser and a photo-lithographic optical system. A laser beam passed through a mask and the pattern was imaged on the film by a pair of convex lenses. As a result, the film was lithographically ablated, and microsized patterns were generated in a single shot. Fringes were generated outside the ablated patterns with defocusing or larger laser fluence. The resolution of generation was 13 μm, and the narrowest width of a generated line was about 4 μm actually.

Nowadays, electronic products used for cellular phones etc. become smaller and more lightweighted, and thus the size of semiconductor boards for integrated circuits need to be reduced. In the case of the cutting process of a thin semiconductor wafer into single chips, conventional processing techniques tend to produce defects. Therefore, we aimed at the development of a new cutting processing technique, i.e. a method with less mechanical and thermal damages. In this study, we investigated the scribing of Al₂O₃ ceramics and of a Si wafer by a nanosecond-laser (Nd:YLF) and a femtosecond-laser (Ti:sapphire). For ceramics, better processing shape with high aspect ratio, no debris, no thermal effect and good processing efficiency were obtained by the femtosecond-laser rather than with the nanosecond-laser. Additionally, the pulse duration of the femtosecond-laser was changed between 30 - 600 fs at fixed processing conditions. When the pulse durations were changed in the femtosecond-range, the shape of the groove bottom and side varied. The processing efficiency was improved with increasing the pulse duration in the range of 30 - 600 fs, which was a finding contrary to results expected. The scribing of the Si wafer shows a similar tendency to that of the Al₂O₃ ceramics. We therefore conclude that the processing shape and the processing efficiency can be improved depending on the pulse duration.

Laser processing using light sources with ultrashort pulses was applied to solid/liquid interfaces. A single-shot 200-fs pulse light was simply focused and irradiated or two pulses were interfered and irradiated at a water or electrolyte solution/silicon interface. From the measured AFM images on the processed silicon surfaces, several features were revealed, which were characteristic of the laser processing at the solid/liquid interface. First, ring patterns surrounded by sinusoidal patterns like ripples were found within the irradiated spot. Secondly, the processed depth was reduced by coexisting electrolyte in water. Thirdly, there were less residual aggregates or debris.

We have investigated laser etching that removed ITO (Indium Tin Oxide) thin films deposited on glass substrate directly and selectively by laser beam in dry process. At first, in order to examine the dependence of laser wavelengths at ablation, the first, second, third and fourth harmonic of nanosecond pulsed Nd:YLF laser were employed respectively. As a result, comparatively good etching was performed by the UV wavelength. In the line patterning of ITO, however, molten materials were observed around the edge of the pattern. Moreover, a few micro cracks occurred in the molten domain. In this research, therefore, we carried out laser etching by ultra-short pulsed laser (wavelength: λ = 800 nm, pulse duration: 30 fs) to solve these heat influence problems. The line patterning of ITO (film thickess: 330 nm) was performed by control of laser fluence at fixed laser power and feed rate. In conclusion, we achieved good laser etching that the molten materials and the micro cracks were reduced and there were little debris near the groove, even processing in the atmosphere. Additionally, the removal of ITO was more efficiency as compared with nanosecond-laser so that effects of plasma shielding were lower at ablation.

Commercial femtosecond micromachining system (FMS) has been developed that capable to process the material in sub-micron (< 200 nm) and micron scale. Core of the system are: optical unit, controller unit and software. The other parts: fs-laser system; focusing unit; stage unit can be varied (exchangeable). Two different fs-laser systems already are compatible with core of FMS: Mira/RegA (Coherent) and Hurricane (Spectra-Physics). FMS controller unit allows to control every single fs-pulse delivery on the target. Three possible types of focusing unit are available: microscope type unit, long focal distance lens unit, and axicon lens based unit. Standard stage unit options are: three-axis piezostage, and two-axis air bearing stage combined with Z-axis piezostage. Repeatability for all dimensions is within ±5 nm. Also, step motor stages are available. The system allows 3D scan with confocal laser-microscope (resolution δr=200nm, δz=540nm) build in optical unit. Software controls all basic functions of the system performance and writing any pattern (including 3D) on or into specimen. The results obtained by direct fs-laser writing method are presented and discussed: bits in the range of 100 - 200 nm sizes, 6 TB/cm³ density optical storage matrix, waveguides fabrication inside transparent materials, high aspect ratio (1:125) patterning of dielectric materials with Gauss-Bessel beam.

Micro scaled grooves and cavities are fabricated with the method of direct writing and superposing grooving in ambient air using femtosecond laser pulses and copper, aiming at establishing an industrially useful femtosecond laser processing machine to be able to fabricate three dimensional micro-scale structures, especially micro scaled molds, and processing techniques. The following items are demanded to make femtosecond laser processing machine an industrially useful tool. (1) There is no thermally influenced region around the area irradiated by the laser beam. (2) Surfaces irradiated laser beam are smooth. (3) Substances ablated to form are not attached on the surface of the work. In this study, fundamental properties of grooving and cavity processing are investigated experimentally, considering above items, especially eyeing on the items (1) and (2). As a result obtained in this research, the method of direct writing and superposing grooving havs a potential to fabricate micro scaled structure.

Higher and higher through-puts in marking industry are todays requirements. Mainly packaging industry or cable marking companies ask for part-by-part varying markings like serial numbers, weight, date or barcodes. That gives a need to develop a flexible, high-speed on-the-fly marking technique. Current laser marking techniques like direct writing using a scanned laser beam or excimer laser fixed mask projection offer proven quality and either flexibility or detailism. Their drawbacks are limited speed (direct writing) and invariability (fixed mask projection). The Fraunhofer IWS developed a marking system using excimer laser mask projection with a micro mirror device (MMD) as computer-controlled 'flexible mask.' The idea is to generate complex markings within one laser pulse so the marking speed is only limited by the laser repetition rate. The IWS used a 308nm excimer laser and a reflective phase-shifting mask from Fh IMS to demonstrate the marking capabilities. It was possible to generate free-programmable, high-contrast markings on common materials like paper and plastic. Furthermore, it could be shown that the technique is also usable to generate 3D structures in PI. Result of the studies is the development of a very fast marking technique using MMDs in combination with short wavelength and short pulse lasers. It also has high potential in 3D laser micromachining.

We present a novel technique for engraving microscopic 2D patterns in one step with a UV pulsed laser by means of a versatile programmable approach. The laser beam is divided to an expanded low energy signal beam which is spatially modulated by a LCD modulator and a higher energy pump beam with a plane homogeneous wave front. Both beams are superposed in a highly magnesium doped photorefractive lithium-niobate crystal where an energy transfer towards the weaker signal beam takes place. The spatially modulated and amplified signal beam is then de-magnified and imaged onto the surface where the image has to be engraved. The need for the coherent amplifier rises out of the fact that LCDs are unable to withstand the high energy throughput required for etching. The combination of the amplifier with the amplitude modulator leads to a faster and more flexible solution than laser marking with pixel-by-pixel raster-scan, or fixed mask projection mode. Such a technique can thus be applied to identify valuable items by imprinting a smart and personalized 2D code onto its surface.

Laser drilling has become a valuable tool for the manufacture of high precision micro holes in a variety of materials. Laser drilled precision holes have applications in the automotive, aerospace, medical and sensor industry for flow control applications. The technology is competing with conventional machining micro electro-discharge machining in the field of fuel injection nozzle for combustion engines. Depending on the application, laser and optics have to be chosen which suits the requirements. In this paper, the results achieved with different lasers and drilling techniques will be compared to the hole specifications in flow control applications. The issue of geometry control of high aspect ratio laser drilled holes in metals will be investigated. The comparison of flow measurement results to microscopic hole dimension measurement show that flow characteristics strongly depend on cavitation number during flow.

A shadowgraphic imaging technique is used for studying the interaction between the laser beam and the material during laser drilling. The used laser is a XeCl excimer laser with a nearly diffraction limited beam and 175 ns pulse length. We studied how and when the material is removed. Holes are drilled with a series of pulses in aluminum and Hastelloy X. The shadowgraphic images show the development of a shockwave whose expansion is in agreement with theory. Both the removal of material at different times after the start of the laser pulse and the material removal for different pulses during the drilling process are shown. Material removal occurs by vaporization as well as melt ejection. Our experiments show the same amount of removed material for drilling with different cover gases. The shadowgraphic images show that the larger part of the material is removed after the end of the laser pulse.

To meet the industry's demand for reducing machine cycle lengths concerning laser-drilling a Nd:YAG Master-Oscillator Power-Amplifier (MOPA)-system was developed at the LMTB-laboratories that emits high-power peak-pulses at excellent beam-quality. Presently, the output power of the oscillator (10W@1064nm) with a beam-quality of M² = 1.3 is amplified to 95W@1064 nm with M²=2.3 and a single pulse energy up to 500 mJ. The pulse duration can be varied between 26 and 230 ns. On account of the excellent beam quality, frequency conversion resulted in 49W@532nm and 4.8@266nm. The MOPA-System is used for laser micro drilling experiments into metals and ceramics where the influence of the beam quality on the geometrical shape of the hole is investigated and compared with applications conducted with similar laser systems. Additionally means in optimizing the drilling process such as burr-minimizing and melt-reduction were introduced. Furthermore, experiments using tapered drilling technique are undertaken. A maximum aspect ratio of 1:200 in stainless steel was obtained.

The shape of a processed hole is a key factor for laser drilling system. There are many studies to calculate the behavior of heat or the reaction of molecules in a substrate after laser irradiation. These simulations enable calculation of removed volume by laser power. However, there were some difficulties to estimate the shape of processed hole. To solve the problem, the shape of processed hole was calculated by optical simulation and the ablation rate. The laser intensity distribution on the substrate was calculated by optical simulation considered with diffraction of beam and the aberrations of optics. Furthermore the results of optical simulation were rectified by ablation rate. The calculated shape of the processed hole showed good agreement with actual. This simulation can be used to control the laser drilling process to realize high quality holes.

The demand for uniform intensity distribution is rising rapidly in the field of thermal processing. In this study we propose beam homogenizers with aspheric lenses or diffractive optical elements (DOE) that can convert a non-uniform Gaussian distribution into a top-hat-shaped uniform intensity distribution. The circular beam homogenizer consists of two aspheric lenses. And we propose several types of beam homogenizer, namely, rectangular and linear using DOE technology. Especially, we present a spot array generation homogenizer that can anneal several points simultaneously. This paper suggests possibilities of advance laser optics for new types of laser material processing.

There are large number of processing conditions which can be set for laser-cutting of plate materials, because importance of the objective for the cutting is different from product to product. This study aims to build a system which can set the processing conditions reasonably and efficiently. From plural processing objectives, roughness of cutting surface was taken up from among the required qualities, such as processing speed, circularity of a processed hole, height of dross on the rear side, roughness of cutting surfaces, accuracy of shapes and dimensions, and with of burning, to review the effects of the processing condition on the cutting surface including the drag line gap. In our experiments, a 1 kW CO₂ gas laser machine was used to make laser-cutting samples and 389 combinations of samples were used. From the results of the experiments, the range of processing conditions which allow cutting is defined by the energy input per unit area HIA = 4.8 [J/mm²]. The values of roughness of the cutting surface on both front and rear sides of the plates can be reduced if the cutting speed is 1000 mm/min or higher, and they little change at small values if the heat input per unit area is within a range under 20 J/mm². In a range of thin plate thickness, the drag gap on cutting surfaces can be evaluated by the heat input per unit area. In the case of thicker plate, the greater the duty is, the smaller the drag gap is, if the heat input per units area is kept unchanged. Cutting with small heat input is desirable for better roughness of cutting surface. Cutting with large heat input is required for better drag gap. In the scope of our study, a value 20 J/mm² of heat input per unit area is recommended for laer-cutting of 0.8 - 4.5 mm thick mild steel plates.

This article discusses the latest developments and possibilities of industrial processing brittle materials (e.g., glass, ceramic, ...) with a laser beam. Conventional methods such as scoring with metal or tungsten carbide wheel, diamond, etc., followed by breaking, have long been established in glass processing. These methods have reached the limits of their technical and technological development and defy further improvement. Certain drawbacks, such as the production of glass dust or microcracking at the separating edge, cannot be avoided. These and other disadvantages can be compensated with laser processing.

We have achieved a high-quality beam generation wih highly efficient quasi-cw Nd:YAG laser over 1-kW with a novel side-pumping configuration using micro-lens free diode-stacks as a part of "Advanced Photon Processing and Measurement Technologies" program. We have demonstrated a power scaling of Nd:YAG rod laser over 1 kW while maintaining high-beam-quality and high-efficiency by cascaded-coupling of two identical bifocusing compensation resonators. Laser power of 1050W was obtained with the beam quality of M² = 8 at the electric-to-optical efficiency of 23%. In this work, we also demonstrated the focusing ability of less than 50 μm diameter on the focal plane by using a f50mm lens (N.A. 0.2). Moreover, with driving AO-Q switch in burst mode operation, over 2MW pulse peek is demonstrated.

Trepanning of 200 μm holes in 2-5mm thick CMSX-4 sheets is done by laser radiation provided by a lamp-pumped Nd:YAG slab laser with pulse durations of 100 - 500 μs. Pulse energies <1J determine the material removal mainly by melt expulsion assisted by a processing gas jet coaxial to the laser beam. Stagnation and deflection of the gas jet at the entrance of the kerf, friction in the molten material, and friction at the liquid/solid interface hinder an efficient melt expulsion. A simulation tool for supersonic gas flow solving Euler equations by the Finite Volume Method is developed in order to investigate the gas flow through the trepanning kerf. Gas pressures above and within the kerfs while trepanning at different inclination angles, geometries and arrangements of nozzles as well nozzle reservoir pressures are presented. The computed gas flow is compared to melt expulsion investigated metallographically by the determination of kerf widths and the thickness of the resolidified melt.

A laser shock cleaning (LSC) technique as a new dry cleaning methodology has been applied to remove micro and nano-scale inorganic particulate contaminants. Shock wave is generated in the air just above the wafer surface by focusing intensive laser beam. The velocity of shock wave can be controlled to 10,000 m/sec. The sub-micron sized silica and alumina particles are attempted to remove from bare silicon wafer surfaces. More than 95% of removal efficiency of the both particles are carried out by the laser-induced airborne shock waves. In the final, a removal of nano-scale slurry particles from real patterned wafers are successfully demonstrated by LSC after chemical-mechanical polishing (CMP) process.

Generation of versatile periodic 3d structures with sub-micron precision on material surfaces is demonstrated. The technique is based on a novel beam splitting scheme applying separate diffractive elements. The incoming beam is split into multiple beams whose phase relations are controlled with almost arbitrary precision by only changing the distance between the diffractive elements. Combining this technique with a reflective imaging system, temporal and spatial overlap of all beams with interferometric precision is automatically obtained. The periodic 3d structures are generated through multi-beam interference in the overlapping region of the beams. The shape of the resulting pattern depends on the phase relationship of the interfering beams and can be strongly altered by simple translation of only one diffractive element. We demonstrate the capability of the method for femtosecond laser treatment of solids. Using sub picosecond laser pulses at 248 nm, sub-micron features with different shapes are ablated on the surface of polyimide samples. The size of the achieved structures is well below 1 micron, in special cases even reaching the 100 nm limit.

We have developed the laser nanoprocessing technique by the integration of the ultrafast laser and near-field scanning microscopy (NSOM). The second harmonic femtosecond laser working in the optical near-field with the assistance of NSOM equipment was applied to expose the photosensitive polymer material. The nanopatterns with feature size smaller than the laser wavelength can be fabricated. The optical diffraction limitation is therefore broken through by the near-field nanoprocessing. It was found in our experiment that the nanofabrication feature size depends strongly on the gap between the fiber probe tip and the substrate surface, as well as the laser coupling efficiency. The approach offers the advantages of high precision, speed and selectivity in nanopatterning, and is promising to be used in data storage device manufacture for higher density recording.

A method to create sub-micron changes of the chemical composition of silica based optical fibers is reviewed. The method is used to create thermally stable refractive index structures, Fiber Bragg gratings, which can be used e.g. as sensors operating at very high temperatures. The method is based on UV induced chemical reactions of the silica glass with in-diffused molecular hydrogen. A change in the chemical composition is attained after thermal treatment, and the mechanism is attributed to diffusion of hydrogen compounds within the glass.

The impressing growth of Wavelength Division Multiplexing (WDM) transmissions has pushed the development of photo-induced Bragg gratings in optical fibers. Numerous studies on the photosensitivity of germanosilicate fibers have then been carried out since its discovery in 1978, to understand, stabilize and enhance the effect. Some of those studies are presented here together with some illustrating applications.

A self-trapped filament of ultrashort laser pulses can induce a several-hundred-micron-long region of refractive-index change in silica glass. The maximum refractive-index change and the diameter of refractive-index change are approximately 0.01 and 2 μm, respectively. The filament is 10 - 500 μm long along the pulse propagation axis and its length depends mainly on the numerical aperture of the focusing lens. In this paper, we present the fabrication experiment of volume gratings induced in silica glass by a self-trapped filament of ultrashort pulses. When the 150-μm-long filament was translated perpendicular to the optical axis by 300 μm, a layer of refractive-index change with the thickness of 2 μm was induced. We stacked the layers with a period of several microns and fabricated volume gratings. We entered a He-Ne laser beam at the wavelength of 632.8 nm to the grating with the Bragg angle to measure the diffraction efficiency. The maximum diffraction efficiency was 74.8% with the grating that had the period of 3 μm, and the thickness of 150 μm.

The high peak powers of ultra short (ps and sub-ps) pulsed lasers available at relatively low single pulse energies potentially allow for a precise localization of photon energy, either on the surface or inside (transparent) materials. Three dimensional micro structuring of bulk transparent media without any sign of mechanical cracking has shown the potential of ultra short laser processing. In this study, the micro structuring of bulk transparent media was used to modify fused silica and especially the cladding-core interface in normal fused silica wave guides. The idea behind this technique is to enforce a local mismatch for total reflection at the interface at minimal mechanic stress to overcome the barrier for enhanced optical out-coupling. The laser-induced modifications were studied in dependence of pulse width, focal alignment, single pulse energy and pulse overlap. Micro traces with a thickness between 3 and 8 μm were generated with a spacing of 10 μm in the subsurface region using sub-ps and ps laser pulses at a wavelength of 800 nm. The optical leakage enforced by a micro spiral pattern is significant and can be utilized for medical applications or potentially also for telecommunications and fiber laser technology.

In this article the fabrication of grating structures in the surface of planar polymer chips by the phase mask method is discussed. By this way surface relief gratings (SRG) and bragg-structures can be generated by UV-laser irradiation. Especially the topographical surface properties of the gratings have been examined. Potential applications are the field of optical sensor and information technology.

We report the characterization of waveguiding devices fabricated in optical materials using a femtosecond pulse train from a Ti:Sapphire laser at a 25 MHz repetition rate. Both interferometry and micro-thermal analysis have been used as diagnostics to evaluate optical and structural changes within the glass matrix. A free-electron model is developed to explain the refractive index change.

Waveguide filters with extremely thermally stabilized KrF laser-induced gratings were fabricated in the highly photosensitive Ge-B-SiO₂ thin films. It was discovered that a completely new-type grating with high diffraction efficiency and thermal stability could be formed by annealing a conventional laser-induced grating at 600°C. Such thermally induced gratings couldn't be erased after repeated heat treatment alternating between room temperature and 600°C. We printed a grating in slab waveguide by irradiation with a KrF excimer laser followed by the annealing at 600°C, and then formed the channel in the region of the grating using standard photolithography process. The diffraction peak of 17 dB in depth at 1535.04 nm wavelength was observed after repeated heat treatment alternating between room temperature and 400°C. These thermally stabilized waveguide filters are promising candidate for the highly reliable optical and sensing devices.

As the demand for semiconductor devices based upon ever-thinner silicon substrates continues to increase, mechanical techniques suitable for dicing wafers appear to be approaching their practical limits. Recent advances in power scaling have now enabled reliable ultraviolet-wavelength lasers to be considered to offer a flexible solution to this dilemma. This paper presents new data on the machining of thin silicon wavers using a high average power 355-nm wavelength pulsed laser. In particular, the concept of pulse repetition-rate scaling of the effective cutting speeds was investigated to determine the preferred direction for further laser development efforts.

Material laser cutting is well known and widely used in industrial processes, including micro fabrication. An increasing number of applications require nevertheless a superior machining quality than can be achieved using this method. A possibility to increase the cut quality is to opt for the water-jet guided laser technology. In this technique the laser is conducted to the work piece by total internal reflection in a thin stable water-jet, comparable to the core of an optical fiber. The water jet guided laser technique was developed originally in order to reduce the heat damaged zone near the cut, but in fact many other advantages were observed due to the usage of a water-jet instead of an assist gas stream applied in conventional laser cutting. In brief, the advantages are three-fold: the absence of divergence due to light guiding, the efficient melt expulsion, and optimum work piece cooling. In this presentation we will give an overview on several industrial applications of the water-jet guided laser technique. These applications range from the cutting of CBN or ferrite cores to the dicing of thin wafers and the manufacturing of stencils, each illustrates the important impact of the water-jet usage.

Aluminum nitride (AN) is beginning to replace alumina as a substrate and heat sink for electronic circuits. The thermal conductivity of A1N, about 8 times that of alumina, is the primary reason for its selection in these applications. While beryllium oxide has even higher conductivity, concerns about that material's toxicity reduce its appeal. Alumina is easily scribed and cut with carbon dioxide lasers. The high thermal conductivity that makes AIN useful, however, makes it difficult to machine with a laser because the material can absorb considerable incident energy without melting or vaporizing. Process settings that produce good results with alumina are not suitable for AIN. It is therefore necessary to develop a new processing regime for aluminum nitride. We cut 0.7 mm thick aluminum nitride sheet with a carbon dioxide laser using a large matrix of process variables and examined the resulting edges for surface quality, microcracking, aluminum deposition and recast. With this information, we defined the volume in process space where effective processing can be accomplished.

The laser scribing process is a perspective technique to produce grooves on brittle materials. In this study, we investigated the microscribing of Al₂O₃ ceramics with a diode-pumped Nd:YLF laser. The groove width, the groove depth and the debris height were chosen as evaluation items of the processing. Firstly, we examined the differences in the measurements of these entities by a stylus profilometer, a laser microscope, and a scanning electron microscope (SEM). According to this, the laser microscopic analysis proved to be more reliable than the stylus profilometer, but the SEM observation of the cross-section is desirable for narrow grooves. Secondly, the effects of the focal position of the laser and of the wavelength on the scribing characteristics were investigated in the fundamental mode (λ = 1047 nm) and the second (λ = 524 nm), the third (λ = 349 nm) and the fourth harmonics (λ = 262 nm). In addition, the effects of the feed rate and the number of laser scans were investigated using the third harmonic. As a result, we found that the grooves become sharp and finally remain unchanged with increasing the number of laser scans, the fourth harmonic is very suitable, and an optimal processing speed feed rate exists.

In the harmonic generation using nonlinear optical crystals, phase-matching technique is indispensable for obtaining high conversion efficiency. As the first step of our study, we have investigated crystal temperature variation induced by laser absorption and its influence on conversion efficiency and beam profile in second harmonic generation (SHG) by solving the coupling problem composed of heat conduction equation and complex amplitude equations. In this study, we focused on the declination of irradiation angle of laser from the phase matching angle, which is equivalent to the declination of cut angle of crystal. The influences of angle declination and temperature rise of the crystal on SHG characteristics were examined by supposing KTiOPO₄ (KTP) crystal. Main results obtained are as follows: When the angle declination is only 0.1 deg, conversion efficiency easily decreases to half that under perfect phase-matching condition. Significant distortion of output beam profile of second harmonic is also caused by the angle declination. This essential problem on output beam profile should be considered in precision microfabrication. Influences of angle declination and temperature change on phase mismatching are superposed. Our analysis is useful to elucidate such compounded and complicated phenomena in frequency conversion. A possibility of cancellation of phase mismatching due to angle declination by keeping crystal temperature higher than phase matching temperature was suggested through numerical examples.

Frequency conversion technique using nonlinear optical crystals is indispensible to solid-state laser applications. It is well known that the conversion efficiency is very sensitive to temperature change of crystal, which is caused by laser absorption. We have been analyzing problems of second harmonic generation (SHG) by coupling the electric field to the temperature field. In this study, temporal pulse-shape dependence of SHG was investigated theoretically, and Gaussian pulse and rectangular pulse were compared. Main conclusions obtained are as follows: (1) Both conversion efficiencies with Gaussian and rectangular pulses fluctuate with irradiation time, however the former fluctuation is slower and more gentle. (2) Pulse of output second harmonic fluctuates most remarkably at the center, where power density of incident fundamental is highest, in the Gaussian pulse. (3) As a result, pre-pulse and post-pulse are generated at both sides of the main pulse. (4) Such distortion of output pulse shape becomes more remarkable as power density increases.

Lasers are now widely used in various industrial circumstances with changeable room conditions. If the humidity and the temperature in an operation room are not well controlled, a thin layer of water can be formed on the surfaces of laser optics by the effect of "dewfall," which could cause damages of expensive laser optics such as output coupler and/or focusing lenses. In this work, we design and develop an alarm device to monitor and control the dewfall for industrial CO₂ lasers; however, the device is also useful in other cases which require alarm and control of dewfall.