This PDF file contains the front matter associated with SPIE Proceedings Volume 7584, including the Title Page, Copyright information, Table of Contents, the Conference Committee listing, and Introduction.

By laser-induced backside wet etching (LIBWE), we can fabricate deep microstructures with high aspect ratios. To fabricate such deep microstructures by means of a mask-projection system, appropriate optimization of the sample positions is indispensable to maintain the imaging conditions of the mask-projection system at the etch front. By applying the appropriate optimization, the trenches with homogeneous widths and high aspect ratios could be fabricated. At present, a trench with an aspect ratio of 102 (width: 9.7 μm, depth: 986 μm) was successfully prepared. When the irradiated area was gradually shifted in a direction perpendicular to the incidence of the laser beam, inclined features could be fabricated in the deep microtrenches. The tilting angles of the features could be can be flexibly controlled between -30° and +30° by changing the shifting speed. Moreover, the angles could be varied within a single deep microtrench. Fabrication of deep microhole array was also demonstrated. Fabricated microholes were converted into through holes on grinding.

High intensity intensity ultraviolet (UV) and vacuum ultraviolet (VUV) radiation provide a singular dominant narrow-band emission at various wavelengths(λ) between 108 - 351 nm. The use of dielectric-barrier discharges in its embodiment of an excimer lamp as a photon-source provides a novel method to induce surface modification. From its in relatively humble beginnings in ozone generation, the excimer lamp has found new applications in the field of low-temperature processing of surfaces. Herein, a 15 year perspective of work done at the Materials & Devices Group at University College London between 1992 and 2007 is presented. The excimer lamps' application to the modification of surfaces for materials processing include: photo-induced formation of high-κ dielectric thin films and more recently the UV-induced photo-doping of silicon substrates, amongst others. With its robust yet inexpensive setup and flexibility of geometric configurations, they are easily coupled in parallel resulting in the provision of high photon fluxes over large areas. These sources also have an incoherent and almost monochromatic selectivity for application to process chemical pathway specific tasks by simple variation of the discharge gas mixture. These sources are an interesting addition to and an alternative to lasers for scalable industrial applications and have potential for a myriad of applications across different fields.

Parallel femtosecond laser processing using a computer-generated hologram (CGH) displayed on a spatial light modulator, called holographic femtosecond laser processing, has advantages of high throughput and high light-use efficiency of the laser pulse energy. We demonstrate two types of the holographic femtosecond laser processing that are implemented with a Fourier transform CGH and a Fresnel transform CGH. We present some demonstrations of twodimensional and three-dimensional parallel laser processing.

Top down technology of ultra-short pulse laser processing was applied to induce liquidly process and generate new nanostructures such as nanobump, bead-on-bump and burst structure. Bilayer thin film was used as a sample, and structure changed by the film formation. For example, Burst structure could be generated in the case of Au on Ag film structure. In the case of Ag on Au structure, only nanobump and bead-on-bump structure could be generated, and which is similar to single layer case.

A compact ultra-broadband femtosecond laser scanning microscope with 12 femtoseconds pulse width at the focal plane of a high NA objective has been employed in material nanoprocessing. The laser works at 85 MHz with an M-shaped emission spectrum with maxima at 770 nm and 827 nm. Different motorized setups based on the introduction of chirped mirrors, flint glass wedges, and glass blocks have been realized to vary the in situ pulse length from 12 femtoseconds up to 3 picoseconds. Nanoprocessing was performed in silica, photoresists, glass, polymers, and biological structures. Mean powers as low as 2 mW were sufficient to realize plasma-mediated cutting effects in human chromosomes with sub-80 nm cut width. Using a mean power of 7-9 mW, transient nanoholes were "drilled" in the cellular membrane for targeted transfection of stem cells and the introduction of μRNA probes. Region of interest (ROI) scanning have been used for optical cleaning of human adult stem cell populations and blood cell suspensions. 3D two-photon nanolithography based on the ultrabroad band laser pulses was realized with the photoresist SU-8. Multiphoton sub-20fs microscopes may become novel non-invasive 3D tools for highly precise nanoprocessing of inorganic and organic targets.

A parallel processing of two-photon polymerization structuring is demonstrated with spatial light modulator. Spatial light modulator generates multi-focus spots on the sample surface via phase modulation technique controlled by computer generated hologram pattern. Each focus spot can be individually controlled in position and laser intensity with computer generated hologram pattern displayed on spatial light modulator. The multi-focus spots two-photon polymerization achieves the fabrication of asymmetric structure. Moreover, smooth sine curved polymerized line with amplitude of 5 μm and a period of 200 μm was obtained by fast switching of CGH pattern.

Using an ultrashort pulse laser, photon energy of which is smaller than the band gap energy of silicon, machining of substances located at back of a silicon plate should be achievable. To realize this possibility, machining of a silicon substrate as well as machining of gold film on it was carried out using femtosecond laser pulses, wavelength of which lay between 1.5 to 2.5 μm. It is demonstrated that the rare surface of the silicon substrate and the gold film placed at the back of the silicon substrate can be machined with no detectable change on its front surface. Frequency adjustment of crystal oscillator sealed in a silicon package is tried and up-conversion of the frequency is achieved by removing small amount of thin gold film on the crystal with irradiation of 1.5 μm laser pulses through the silicon lid.

Spatial distributions of proteins are crucial for development, growth and normal life of organisms. Position of cells in a morphogen gradient determines their differentiation in a specific manner. Neutrophils are the initial responders to bacterial infection or other inflammatory stimuli and have the ability to migrate rapidly up shallow gradients of attractants in vivo. Moreover, for the correct wiring of the nervous system, axonal growth cones detect concentration changes of specific proteins called guidance cues to navigate and reach their targets. Guidance cues can either be chemoattractive or chemorepulsive, and the same protein can act successively as both depending on the time point in development or the simultaneous presence of other molecules. A prerequisite to understand chemotaxis in a precise manner is the availability of a method able to reproduce in vitro the spatial distributions of proteins found in vivo. We recently introduced LAPAP (Laser-assisted protein adsoption by photobleaching), an optical method to produce substrate-bound protein patterns with micron resolution. Here, we present how the amount of protein present on the pattern can be increased by one order of magnitude.

We demonstrate fabrication of microfluidic chips integrated with different functional elements such as optical filters and optical waveguide for mechanism study of gliding movement of Phormidium to a seedling root using a femtosecond (fs) laser. Fs laser direct writing followed by annealing and successive wet etching in dilute hydrofluoric (HF) acid solution resulted in formation of three dimensional (3D) hollow microstructures embedded in a photostructurable glass. The embedded microfludic structures enabled us to easily and efficiently observe Phormidium gliding to the seedling root, which accelerates growth of the seedling. In addition, fabrication of optical filter and optical waveguide integrated with the microfluidic structures in the microchip clarified the mechanism of the gliding movement. Such microchips, referred to as a nano-aquarium, realize the efficient and highly functional observation and analysis of the gliding movement of Phormidium.

Ultra short (ps, fs) laser pulses are used, when high requirements concerning accuracy, surface roughness, heat affected zone etc. are demanded for surface structuring. Ps-laser systems that are suited to be operated in industrial environments are of great interest for many practical applications. Here results in the field of 3-d structuring (metals and transparent materials), induced processes and structuring of flexible solar cells will be presented. Beside the pulse duration, which is given by the laser system, the user has a wide variety of optimization parameters such as fluence, repetition rate and wavelength. Based on a simple model it will be shown, that there exist optimum laser parameters to achieve maximum volume ablation rates at a given average power. To take benefit of these optimum parameters and to prevent harmful effects like plasma shielding and surface melting, adapted structuring strategies, depending on the requirements, have to be used. Today's ultra short pulsed systems have average powers from a few W up to a few 10W at high repetition rates. The actual available beam guiding systems are limited and can often not fulfill the requirements needed for high throughput structuring with optimized parameters. Based on the achieved results, the needs for future beam guiding systems will be discussed.

We describe a novel process of laser-assisted fabrication of surface structures on doped oxide glasses with heights reaching 10 - 13% of the glass thickness. This effect manifests itself as a swelling of the irradiated portion of the glass, and occurs in a wide range of glass compositions. The extent of such swelling depends on the glass base composition. Doping with Fe, Ti, Co, Ce, and other transition metals allows for adjusting the absorption of the glass and maximizing the feature size. In the case of bumps grown on borosilicate glasses, we observe reversible glass swelling and the bump height can increase or decrease depending on whether the consecutive laser pulse has higher or lower energy compared with the previous one. To understand the hypothetical mechanism, which includes laser heating of glass, glass melting, and directional flow, we explored density, refractive index, fictive temperature, and phase separation dynamics.

Lasers are becoming increasingly important in today's LED revolution and are essential for increasing the efficiency and reducing manufacturing cost of LEDs. Excimer lasers provide unique homogeneous illumination of large areas, and are ideally suited for laser lift off (LLO) of the LED film from the sapphire substrate used for epitaxial growth. In this paper we will discuss the excimer laser lift off technique for manufacturing vertical type LEDs, and how it can be applied to GaN and AlN based LEDs. On the other hand, diode pumped solid state lasers excel in scribing and cutting of a number of materials relevant to the LED industry: sapphire, silicon, silicon carbide, III-nitrides (gallium nitride and aluminum nitride), as well as III-V semiconductors (gallium arsenide, gallium phosphide). In this paper we will discuss some of the recent laser scribing techniques and how adequate selection of laser parameters and beam delivery optics allows for a high quality high throughput process.

The recent advancements in technology of compact laser plasma EUV sources based on a gas puff target are presented in the paper. The sources have been developed for application in processing materials using EUV radiation in the wavelength range from about 5 nm to about 50 nm that is efficiently produced in result of irradiation a double-stream gas puff target with high-intensity laser pulses from a Nd:YAG laser (0.8 J/4 ns/10 Hz). The sources can be equipped with two various grazing incidence optical systems to focus EUV radiation: an axisymmetrical ellipsoidal mirror or a multifoil mirror system of the "lobster eye" type. A new design of the laser plasma EUV source dedicated for micro- and nanoprocessing polymers and modification of polymer surfaces is presented for the first time.

We describe a method of using femtosecond laser for direct writing of volume Fresnel zone plates with high diffraction efficiency. A volume zone plate consists of a number of Fresnel zone plate layers designed to focus light coherently to a single spot. We fabricated both low numerical aperture (NA) and high NA volume zone plates, resulting in a significant increase in overall diffraction efficiency. The performance of the volume zone plate is also simulated using the Hankel transform beam propagation method (Hankel BPM). The results show an excellent agreement with the scalar diffraction theory and the experimental results. The numerical method allows more comprehensive studies of the VFZP parameters to achieve higher diffraction efficiency.

It has been shown that 30 ns FWHM duration pulses from a MOPA fiber laser (wavelength: 1064 nm) cleanly micromachines silicon with little cracking or heat-affected zone¹. In this paper, we show that similar results can be achieved using a 1070 nm quasi-continuous wave laser pulsed with a 6.6 μs duration (average power: 2.8 W) in combination with coaxially delivered nitrogen assist gas. The holes are cut at a 5 kHz repetition rate with a resulting diameter on the order of 15 μm and an etch rate of up to 18 μm/pulse. Hole size is increased for longer pulses and the heat-affected zone broadens to greater than 25 μm with no assist gas. By combining low coherence microscopy with machining, we depth image the machining front and obtain in situ images during and after the drilling process showing rich cut dynamics in real time.

Metallic glasses have been preferred to crystalline alloys for applications in microelectronics mechanical systems and die components because of their ease of formability and excellent mechanical properties. This paper presents the machining response of amorphous and polycrystalline Ni-based alloys (Ni78 B14 Si8) and Fe alloys (Fe81 B13.5 Si3.5 C2) when subjected to micro-second and pico-second laser processing. The shape and topography of craters created with single pulses as a function of laser energy together with holes drilled and laser milled areas in both materials were studied. Focused ion beam (FIB) imaging and Energy Diffraction Spectroscopy (EDS) were used to analyse the single craters, through holes and milled trenches in the amorphous and polycrystalline samples. The material microstructure analysis revealed that processing both materials with micro-second and pico-second lasers does not lead to crystallisation and the short-range atomic ordering of metallic glasses can be retained. When processing the amorphous sample the material laser interactions resulted in a significant ejection of molten material from the bulk that was then followed by its partial re-deposition around the craters. Additionally, there were no signs of crack formation that indicate a higher surface integrity after laser machining. This integrity is closely related to the nature of the metallic glass. A conclusion is made that laser processing both with short- and long-pulses is a promising technique for micromachining metallic glasses because it does not lead to material crystallisation, preserving the good mechanical properties of these sort of materials.

During the last decade, diode-pumped solid state (DPSS) lasers have been gained wider application in semiconductor and electronics industry due to the advantages of high efficiency, low operating cost, good beam quality and flexibility as well as miniature size. Now, 355nm DPSS UV laser has increasingly been adopted in micro-processing application for both semiconductor and electronics industry where both micro-processing quality and precision of high-density, multilayer and multi-material components are in a strong demand. Our works on typical applications of 355nm DPSS UV laser micro-processing both semiconducting and electronic materials have been introduced in this paper, including drilling (200μm blind holes in 4-layer FPC), cutting (coverlay, CCL, FPC, 0.6mm silicon), and etching (ITO-glass). The effects of the processing parameters (pulse energy, frequency, peak power, scanning speed and focal plane position as well as processing modes) on the micro-processing quality and precision have been investigated and analyzed. By optimizing the processing parameters, the blind drilling depth to the second copper layer can be controlled accurately and the roughness Sq 1.33μm on the second copper surface can be achieved. A high quality and size precision (position precision 20μm) cutting edge without charring, burrs and micro-cracks as well as with very small heat affected zone (HAZ) can be also obtained. When etching function film, the etching width is less than 20 micron, and the etching speed is more than 500mm/s.

Efficient doping of amorphous silicon(a-Si) is a key issue in the field of photovoltaic applications. In this paper an attempt has been made to produce a highly highly textured Sb doped a-Si. The a-Si were coated with Sb to a thickness of 200nm using vacuum evaporation method and treated with an Nd:YAG laser of 355nm with a threshold fluence of 460mJ/cm² by overlapping the laser spots to 90% of its size. The samples are retretaed with a low laser fluence of 230mJ/cm² respectively so as to crytsallize and diffuse the Sb on to the surface and to activate the dopant. The laser doped and subequently laser textured samples were analysed through Scanning Electron microscope (SEM), X-ray diffraction (XRD) & Atomic Force Microscope(AFM).The traces of SiSb in the XRD peak with improved surface roughness were observed on the laser doped samples. This represents that the dopants are highly diffused on the a-Si.

In this paper, micro-surface roughness has been experimentally identified using laser scattering images. At first, previous surface evaluation methods, laser scattering parameters and optical deflected rays are investigated and then laser scattering inspection mechanism is developed. Its optimum parameters on grinding surfaces are selected using a design of experiment. It is shown that the mean of vertical scattering distributions is characterized as wavelet in laser scattering images with the selected optimal parameters. Also, the dominant feature of laser scattering distributions is linearly increased according to grinding surface roughness and so the information can be used as important factor for the measurement and evaluation of various surface roughnesses. The proposed laser scattering method is applied to the evaluation inspection of crystalline silicon wafer surfaces for solar cell.

A model describing laser microhole drilling processes in polymers has been developed, which can predict the drilling profiles of the microholes for several kinds of specific incident beam profiles. The report tries to answer how the peak fluence, the beam diameter (or beam shape), and the material parameters affect the hole shapes. The model not only provides the drilling hole profiles but also explains why hole drilling stops under certain circumstances, such as a stabilized or saturated drilling occurs, under this condition more shots applied to the process will not generate any further drilling effect. Thus high efficient laser processing can be predicted from the model, i.e. what are the best laser parameters for certain processed materials including material thickness. This model is suitable for most well defined beams and materials such as polymers, polyimide, polymethylmethacrylate (PMMA), polyethylene terephthalate (PET), fiber reinforced composites or CFC, glass fiber composites, and some ceramics. This paper mainly concentrates on the modeling, while the comparison of the modeling and the experimental data will be discussed in the other paper to be published in the same volume of SPIE.

A model describing laser microhole drilling processes in polymers has been developed, which can predict the drilling profiles of the microholes for several kinds of specific incident beam profiles. The report tries to answer how the peak fluence, the beam diameter (or beam shape), and the material parameters affect the hole shapes. The model not only provides the drilling hole profiles but also explains why hole drilling stops under certain circumstances, such as a stabilized or saturated drilling occurs, under this condition more shots applied to the process will not generate any further drilling effect. Thus high efficient laser processing can be predicted from the model, i.e. what are the best laser parameters for certain processed materials including material thickness. This model is suitable for most well defined beams and materials such as polymers, polyimide, polymethylmethacrylate (PMMA), polyethylene terephthalate (PET), fiber reinforced composites or CFC, glass fiber composites, and some ceramics. This report mainly concentrates on the comparison of the modeling and the experimental data, it is found that both match extremely well.

Precise control of diffraction peaks of a hologram is indispensable in holographic femtosecond laser processing. To obtain the uniform diffraction peaks, an adaptive optimization due to the diffraction peaks measured by an image sensor was proposed. It used a one-photon absorption. However, the structure processed by a femtosecond laser pulse was based on multi-photon absorptions. Therefore, a mismatch between the optimized diffraction peaks and the processed structures was observed. An adaptive optimization method using second harmonics induced by parallel pulse irradiations to a nonlinear optical crystal is proposed to solve this mismatch.

Near-IR femtosecond (τ = 150 fs, λ=775 nm, repetition rate 1 kHz) and VUV nanosecond (τ = 20 ns, λ=157 nm, repetition rate 1 to 5 Hz) laser pulse ablation of single-crystalline TeO₂ (c-TeO₂, grown by the balance controlled Czochalski growth method) surfaces was performed in air using the direct focusing technique. The multi-method characterization using optical microscopy, atomic force microscopy and scanning electron microscopy revealed the surface morphology of the ablated craters. This allowed us to characterize precisely the lateral and vertical dimensions of the laser-ablated craters for different laser pulse energies and pulse numbers at each spot. Based on the obtained information, we quantitatively determined the ablation threshold fluence for the fs laser irradiation when different pulse numbers were applied to the same spot by using two independent extrapolation techniques. We found that in case of NIR femtosecond laser pulse irradiation, the ablation threshold significantly depends on the number of laser pulses applied to the same spot indicating that incubation effects play an important role in this material. In case of VUV ns laser pulses, the ablation rate is significantly higher due to the high photon energy and the predominantly linear absorption in the material. These results are discussed on the basis of recent models of the interaction of laser pulses with dielectrics.

An optimized 1064nm MOPA fiber laser configuration is used for generating pulse widths from 10 ns to 250 ns, with pulse repetition frequencies that range from single-shot to 500 kHz, and peak powers up to 10kW. These parameters are independently controlled and used to investigate the effect of peak power and pulse energy on material ablation. Test results are demonstrated for processed silicon and ceramic materials using pulse energies up to 0.5 mJ and peak powers up to 10kW. We demonstrate that pulses with high peak powers have shallow penetration depths, as compared to longer pulses. These experimental results are well correlated with those from a theoretical thermal model for silicon ablation that is based on silicon temperature rise as the incident pulse energy is absorbed.

The Ronchi test has been consolidated as one of the most successful and powerful techniques applied to determine the quality of optical surfaces.⁵ In recent years, the development and availability of LCD's (Liquid Crystal Displays) have allowed the incorporation of LCD's instead of the traditional static ruling. The easy change of the characteristics of the fringes in the ruling, such as frequency, position, and geometrical form, transformed this technique into a dynamic test.^{1, 8} Its physical interpretation fully connected with a lateral sheared interferometer ^{5, 6} and some concepts and results associated with the interferometric concept of equivalent wavelenght have been applied in this proposal for the evaluation of optical surfaces. The procedure described here to evaluate an optical surface uses the Ronchi test with the equivalent wavelenght.^{6, 10} This is achieved by registering and computing Ronchigrams obtained by employing, separately, two distinct wavelengths. For a particular mirror, some results are shown in order to demonstrate the enhancement of the test with this proposal.

Femtosecond laser micromachining has emerged as a promising technique for creating three dimensional (3D) microstructures. As an essential building block for microfluidics, homogeneous microfluidic channel with high aspectratio is indispensable for lab-on-a-chip (LOC) applications. Fused silica is considered to be an excellent substrate material for LOC applications due to its low thermal expansion coefficient, low autofluorescence, and exceptional transmittance over a wide spectral range. Microfluidic channels can be directly fabricated inside fused silica by femtosecond laser direct writing followed by a subsequent wet chemical etching. However, the fabricated channels usually display a tapered feature and highly elliptical cross-section with limited length (usually <5 mm) and poor inner surface smoothness, which would hamper their applications. Herein, we demonstrate direct fabrication of homogeneous microfluidic channels embedded in fused silica by femtosecond laser direct writing, followed by wet chemical etching and glass drawing. With these procedures, the homogeneity of the fabricated channels has become excellent. Namely, the taper of the microchannels is greatly reduced while their cross-sectional shape becomes circular after the drawing. In addition, an inner surface smoothness of ~0.2 nm can be realized by this method. Finally, the glass drawing method can lead to centimeters long microfluidic channels with an aspect ratio as high as ~1,000. We expect that these microfluidic channels will have important applications in optofluidics in the future.