This PDF file contains the front matter associated with SPIE Proceedings Volume 9350 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

A method to fabricate metal nanowire gratings and dotted structures on substrates by using femtosecond laser is proposed and experimentally demonstrated. By irradiating femtosecond laser pulses to a platinum thin film deposited on a fused silica substrate, platinum nanowire gratings, which periodicities were comparable to or less than half the laser wavelength, were fabricated. The structures were experimentally analyzed with scanning electron microscopy (SEM), cross sectional imaging with focused ion beam (FIB), and atomic force microscopy (AFM). Moreover, dotted structures were formed in a self-organized manner by changing the number of pulses. The method presented has potential to be used as a simple and high-throughput process for fabrication of metal nanostructures for optical, electrical, and biomedical devices.

New results on development of the Direct Laser Interference Patterning (DLIP) technique using the interference of several beams to directly ablate the material are presented. The method is capable of producing sub-wavelength features not limited by a beam spot size and is an effective method of forming two-dimensional periodic structures on relatively large area with just a single laser shot. Surface texturing speed of DLIP method and the direct laser writing was compared. Fabrication time reduction up to a few orders of magnitude using DLIP was evaluated. The sub-period scanning technique was applied for formation of the complex periodic structures. A new method of laser scanning for fabrication of periodic structures on large areas without any visible stitching signs between laser irradiation spots was tested.

Optical vortices, carrying an orbital angular momentum together with a spin angular momentum, enable us to form chiral structures (e.g. chiral metal needles and chiral polymeric relief) on a nanoscale. The chirality of the fabricated nanostructures can further be controlled merely by the handedness of the optical vortices.

Resonant-infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) has been used to deposit blended, organic thin-films with nanoscale domain sizes of constituent polymers, small molecules, or colloidal nanoparticles. In the emulsion-based RIR-MAPLE process, the target contains a nonpolar, organic solvent phase and a polar, water phase. The emulsion properties have a direct impact on the nanoscale morphology of single-component organic thin films, while the morphology of blended, organic thin films also depends on the RIR-MAPLE deposition mode. In addition to these fundamental aspects, applications of blended organic films (organic solar cells, anti-reflection coatings, and multi-functional surfaces) deposited by emulsion-based RIR-MAPLE are presented. Importantly, domain sizes in the blended films are critical to thin-film functionality.

By utilizing photon energies considerably smaller than the semiconductors’ energy band gap, space-selective modifications can be induced in semiconductors beyond the laser-incident surface. Previously, we demonstrated that back surface modifications could be produced in 500-600 μm thin Si and GaAs wafers independently without affecting the front surface. In this paper, we present our latest studies on trans-wafer processing of semiconductors using a self-developed nanosecond-pulsed thulium fiber laser operating at the wavelength 2 μm. A qualitative study of underlying physical mechanisms responsible for material modification was performed. We explored experimental conditions that will enable many potential applications such as trans-wafer metallization removal for PV cell edge isolation, selective surface annealing and wafer scribing. These processes were investigated by studying the influence of process parameters on the resulting surface morphology, microstructure and electric properties.

Fabrication of fiber Bragg grating (FBG) in single mode microfiber (core diameter: 3.75 μm, cladding diameter: 40 μm) by femtosecond laser pulse radiation is presented. Femtosecond pulse filamentation technique is employed in the pointby-point writing method to inscribe single shot periodic index modification in the core of the microfiber. Prior to writing gratings, a short length (~1.5 mm) of microfiber is fusion spliced between two standard single mode fibers (SMF) in order to improve handling and ease grating fabrication. The kilohertz femtosecond laser pulses operating at center wavelength of 800 nm were tightly focused with an objective lens (40X/ NA=0.75) to confine the pulses into a very tiny focal volume and spatially control index modification. The focused femtosecond pulses create filamentary voids at focal point. For the scanning speed of 534 nm/ Sec, the partial overlapping of void structures produces a periodic index modification in the core with a period of 534 nm and constructs the Bragg reflection spectrum centered at 1550.216 nm. Fabrication of a 1 mm long FBG takes less than 2 seconds for the scanning speed of 0.534 mm/sec. The spectral position of Bragg reflection spectrum can easily be tailored simply by changing pulse scanning speed. The performance analysis of the FBG is examined for temperature and axial strain sensitivity. The grating sensor exhibits the temperature and strain sensitivity of 10 pm/ °C and ~1 pm/ micro-strain, respectively.

We propose herein the “ship-in-a-bottle” integration of three-dimensional (3D) polymeric sinusoidal ridges inside photosensitive glass microfluidic channel by a hybrid subtractive - additive femtosecond laser processing method. It consists of Femtosecond Laser Assisted Wet Etching (FLAE) of a photosensitive Foturan glass followed by Two-Photon Polymerization (TPP) of a SU-8 negative epoxy-resin. Both subtractive and additive processes are carried out using the same set-up with the change of laser focusing objective only. A 522 nm wavelength of the second harmonic generation from an amplified femtosecond Yb-fiber laser (FCPA µJewel D-400, IMRA America, 1045 nm; pulse width 360 fs, repetition rate 200 kHz) was employed for irradiation. The new method allows lowering the size limit of 3D objects created inside channels to smaller details down to the dimensions of a cell, and improve the structure stability. Sinusoidal periodic patterns and ridges are of great use as base scaffolds for building up new structures on their top or for modulating cell migration, guidance and orientation while created interspaces can be exploited for microfluidic applications. The glass microchannel offers robustness and appropriate dynamic flow conditions for cellular studies while the integrated patterns are reducing the size of structure to the level of cells responsiveness. Taking advantage of the ability to directly fabricate 3D complex shapes, both glass channels and polymeric integrated patterns enable us to 3D spatially design biochips for specific applications.

Irradiation of intense ultrafast laser pulses in glasses can lead to formation of nanogratings whose periods are significantly smaller than the incident irradiation wavelength. The mechanism of the exotic phenomenon is still under hot debate. Here, we access the snapshots of morphologies in the laser affected regions in a porous glass which reveal the evolution of the formation of nanogratings with increasing number of laser pulses. Combined with further theoretical analyses, our observation provides important clues which suggest that excitation of standing plasma waves at the interfaces between areas modified and unmodified by the femtosecond laser irradiation plays a crucial role for promoting the growth of periodic nanogratings. The finding indicates that the formation of volume nanogratings induced by irradiation of femtosecond laser pulses is initiated with a mechanism similar to the formation of surface nanoripples.

For high-resolution printing, we have developed a novel way of functional microdots deposition based on laser-induced forward transfer, which is referred to laser-induced dot transfer (LIDT). LIDT is one of promising additive manufacturing techniques because it can realize flexible patterning of micron and submicron-sized dots at atmospheric room-temperature conditions. Recently we have achieved printing of functional oxide microdots by a double-pulse LIDT with the first pulse for preheat and the second pulse for transfer, resulting in more precise control of laser-induced hightemperature and thermal-stress in a source film. In this paper, temporal temperature distributions during the transfer process have been investigated using a finite element method approach. High-resolution printing of functional microdots is promising for future optoelectronic integrations.

The direct write and non-contact nature of laser patterning is highly desirable as it is compatible with integration in rollto-roll production lines. The reduced thermal effects of ultrafast lasers are key to obtain selective removal of sensitive, thin film layers (<0.2µm). In this work, diode-pumped solid state (DPSS) picosecond and femtosecond pulse duration lasers are compared to identify the laser parameters and conditions required to produce high efficiency organic photovoltaics.

Formation of serial interconnects in thin-film solar cells is an important step for upscaling production yield over large areas. Laser scribing is a promising tool for monolithic interconnect formation in CIGS solar cell module. However, evaluation of alterations in electrical properties of the cells during the laser scribing is not a trivial task, especially for cells with flexible substrates when production is based on roll-to-roll processes. We applied the technique of nested circular scribes proposed by K. Zimmer et. al. for the in-line quality evaluation of the P3 scribing processes in CIGS solar cells on polyimide. Scribing experiments were performed using picosecond laser working at 532 nm wavelength. Parallel resistance values of the cells during the formation of P3 scribes were extracted by analyzing I-V characteristics of the measured photovoltaic devices. Integration of laser scribing experiments with the on-line electrical characterization facilitated optimization of the laser processes and increased the measurement accuracy of shunt formation during the laser scribing.

The burst mode for ps and fs pulses for steel and copper is investigated. It is found that the reduction of the energy in a single pulse (in the burst) represents the main factor for the often reported gain in the removal rate using the burst mode e.g. for steel no investigated burst sequence lead to a higher removal rate compared to single pulses at higher repetition rate. But for copper a situation was found where the burst mode leads to a real increase of the removal rate in the range of 20%. Further the burst mode offers the possibility to generate slightly melted flat surfaces with good optical properties in the case of steel. Temperature simulations indicate that the surface state during the burst mode could be responsible for the melting effect or the formation of cavities in clusters which reduces the surface quality.

A carbon fiber reinforced plastic (CFRP) is widely used for automobile, aircraft and so on, because of having high strength, lightweight and weather resistance. A laser is one of useful tools for cutting CFRP. However, a matrix evaporated zone (MEZ) is formed around the laser irradiation area since heat property of the resin is different from that of carbon fiber. It is required for optimizing the laser processing condition to minimize the MEZ. In our experiment, the CFRP plate was cut with a nanosecond laser under air and Ar gas ambience. The ambient gas is an important factor for reduction of MEZ since formation of MEZ might be caused due to an oxidization of carbon fiber and epoxy resin. In order to evaluate the oxidization, spectroscopic analysis was carried out to investigate an ablation plume under air and Ar gas. Furthermore, a surface on CFRP plate was observed with a scanning electron microscope (SEM). As the results, the cutting quality for argon is better than that for air, and the MEZ for Ar gas is smaller than than that for air.

The dynamics of zinc oxide (ZnO) nanoparticles formed in Ar gas of 200 Torr by laser ablation are visualized by ultraviolet Rayleigh scattering imaging. The time-resolved imaging of the ZnO nanoparticles are presented for several conditions of single-pulse ablation and 10 Hz ablation at room temperature. Scattering light from the nanoparticles appeared at 1-2 ms after ablation, and the spatial distribution was a mushroom like swirling cloud. The cloud propagates forward about 2.6 m/s without lateral expansion. In addition, nanoparticle distribution at a substrate heating condition, which is growth condition of ZnO nanocrystals is investigated. The nanoparticles under heating condition formed almost the same spatial distribution as that of room temperature and their speed was increased to 3.2 m/s at 750 °C.

Laser processing of carbon fiber reinforce plastic (CFRP) is a very promising method to solve a lot of the challenges for large-volume production of lightweight constructions in automotive and airplane industries. However, the laser process is actual limited by two main issues. First the quality might be reduced due to thermal damage and second the high process energy needed for sublimation of the carbon fibers requires laser sources with high average power for productive processing. To achieve thermal damage of the CFRP of less than 10μm intensities above 10⁸ W/cm² are needed. To reach these high intensities in the processing area ultra-short pulse laser systems are favored. Unfortunately the average power of commercially available laser systems is up to now in the range of several tens to a few hundred Watt. To sublimate the carbon fibers a large volume specific enthalpy of 85 J/mm³ is necessary. This means for example that cutting of 2 mm thick material with a kerf width of 0.2 mm with industry-typical 100 mm/sec requires several kilowatts of average power. At the IFSW a thin-disk multipass amplifier yielding a maximum average output power of 1100 W (300 kHz, 8 ps, 3.7 mJ) allowed for the first time to process CFRP at this average power and pulse energy level with picosecond pulse duration. With this unique laser system cutting of CFRP with a thickness of 2 mm an effective average cutting speed of 150 mm/sec with a thermal damage below 10μm was demonstrated.

Local melting can be induced inside a glass by focusing femtosecond (fs) laser pulses at high repetition rate (>100kH). As the results, the spatial distributions of glass elements are modified in the molten region. Because various propertied of glasses depends on the composition of elements, the modification of spatial distribution of glass elements using fs laser will make it possible to control glass properties in three dimensional manner. The important point of the control of elemental distribution is how to control the flow of glass melt during laser irradiation. In this study, to elucidate how parallel laser irradiation affects the flow of glass melt during laser irradiation, we investigated the relationship between the flow of glass melt and various irradiation parameters by in-sites observation of flow of glass melt inside a sodalime glass during repetitive photoexcitation by 1 kHz and 250 kHz fs laser pulses at multiple spots.

New wavelengths of laser radiation are of interest for material processing. Results of application of the all-fiber ultrashort pulsed laser emitting in 2 µm range, manufactured by Novae, are presented. Average output power was 4.35 W in a single-spatial-mode beam centered at the 1950 nm wavelength. Pulses duration was 40 ps, and laser operated at 4.2 MHz pulse repetition rate. This performance corresponded to 25 kW of pulse peak power and almost 1 µJ in pulse energy. Material processing was performed using three different focusing lenses (100, 30 and 18 mm) and mechanical stages for the workpiece translation. 2 µm laser radiation is strongly absorbed by some polymers. Swelling of PMMA surface was observed for scanning speed above 5 mm/s using the average power of 3.45 W focused with the 30 mm lens. When scanning speed was reduced below 4 mm/s, ablation of PMMA took place. The swelling of PMMA is a consequence of its melting due to absorbed laser power. Therefore, experiments on butt welding of PMMA and overlapping welding of PMMA with other polymers were performed. Stable joint was achieved for the butt welding of two PMMA blocks with thickness of 5 mm. The laser was used to cut a Kapton film on a paper carrier with the same set-up as previous. The cut width depended on the cutting speed and focusing optics. A perfect cut with a width of 11 µm was achieved at the translation speed of 60 mm/s.

In earlier work the capabilities of synchronizing a galvo scanner or a polygon line scanner with a picosecond laser system in MOPA arrangement were presented. However these systems only enabled precise positioning of laser pulses on the target relatively to each other. Since then a novel approach to increase the absolute precision in positioning has been developed. This improvement enables new and more efficient process strategies such as bidirectional processing or high precision structuring of large areas in combination with additional mechanical axes. These improvements represent a major step towards large scale industrial applications in laser based micromachining.

We present a mobile laser lithography station for 3D structuring by microscopic two-photon polymerization. For structuring the Coherent Vitara UBB titanium:sapphire femtosecond laser is used, which has a power output of 500mW and generates pulses with a central wavelength of 810nm. The laser pulses have a tunable bandwidth from 50nm to 250nm. The pulses are temporally compressed using chirped mirrors to a minimum duration of less than 15fs at the sample. The laser power reaching the sample can be motionless controlled by a combination of a liquid crystal retarder and a polarizer within milliseconds. The sample is placed onto a microscope stage which has a movement range of 300µm in the X, Y and Z direction with an accuracy of 2nm. Sample imaging is possible with a microscope camera simultaneous to the structuring. The pulses are focused by a 40X microscope objective (1.3NA) onto the sample. To operate the lithography station, we developed a LabVIEW-based software which controls sample position, laser power and objective height and as well as the microscope camera. Furthermore, CAD data can be read and converted into sample position data. By combining all these components, a fully automatic structuring of a sample with sub-micrometer precision is possible.

Two kinds of pulsed laser sources, femtosecond laser (fs laser) and nanosecond laser (ns laser), were used in the pulsed laser deposition (PLD) system to synthesize copper indium gallium selenium (CIGS) thin films at the substrate temperature from room temperature (RT) and 500^o C. Different surface morphology, crystallinity, and stoichiometric ratio were observed on CIGS thin films deposited by femtosecond pulsed laser deposition (fs-PLD) and nanosecond pulsed laser deposition (ns-PLD) respectively, that resulted in different optical and electrical properties. It is proposed that the laser absorption of CIGS target with different laser wavelength caused the difference in laser penetration depths into the target, so that the stoichiometric ratio of the evaporated materials splashing from the target were different between fs-PLD and ns-PLD processes.

Real-time acquisition of polarization distribution of light will enable us to treat new image information and give us new application of image acquisition. A polarization imaging filter, which is used to obtain a polarization distribution in realtime, is consist of two-dimensionally arrayed polarizers or waveplates of different orientations. A polarization imaging filter of waveplate-type can be fabricated by inscribing birefringent structure inside a silica glass by focused ultrashort laser pulses. Larger retardance and higher transmittance of a filter are required to acquire the polarization with a higher sensitivity. However, transmittance through inscribed birefringent structures decreases with increasing retardance. Therefore, it is necessary to elucidate the laser processing conditions to obtain larger retardance with maintaining transmittance as possible. In this study, we investigated processing characteristics such as retardance and transmittance which determine the performance of a polarization filter.

A new methodology to estimate the dynamics of femtosecond laser-induced impulsive force generated into water under microscope was developed. In this method, the position shift of the bead in water before and after the femtosecond laser irradiation was investigated experimentally and compared with motion equation assuming stress wave propagation with expansion and collapse the cavitation bubble. In the process of the comparison, parameters of force and time of the stress wave were determined. From these results, dynamics of propagations of shock and stress waves, cavitation bubble generation, and these actions to micro-objects were speculated.

We developed a longitudinally excited CO₂ laser that produces a short laser pulse. The laser was very simple and consisted of a 45-cm-long alumina ceramic pipe with an inner diameter of 9 mm, a pulse power supply, a step-up transformer, a storage capacitance, and a spark-gap switch. The laser pulse had a spike pulse and a pulse tail. The energy of the pulse tail was controlled by adjusting medium gas. Using three types of CO₂ laser pulse with the same spike-pulse energy and the different pulse-tail energy, the characteristics of the hole drilling of synthetic silica glass was investigated. Higher pulse-tail energy gave deeper ablation depth. In the short laser pulse with the spike-pulse energy of 1.2 mJ, the spike pulse width of 162 ns, the pulse-tail energy of 24.6 mJ, and the pulse-tail length of 29.6 μs, 1000 shots irradiation produced the ablation depth of 988 μm. In the hole drilling of synthetic silica glass by the CO₂ laser, a crack-free process was realized.

Extraordinary light transmission effect on a metal surface, also known as surface plasmon resonance, has been widely discussed in recent years. Extending from this line of research, surface plasmons generated by subwavelength annular apertures (SAA) on metallic film has been identified to have the ability to create sub-wavelength Bessel-like beams. It has also been found that this type of Bessel beam can be used to produce high-aspect ratio microstructures when adopted in laser micromachining. However, the drawback is that the Bessel beams produced by the SAA structure is often characterized as having a low transmission efficiency and high side lobes. In order to improve these shortcomings, an improved SAA-like structure is proposed in this paper. A new photon-sieve replaces the annular aperture by an array of holes which can lower the side lobes of the emitted Bessel beams. More specifically, the original ring-shaped holes are now replaced by a series of smaller holes arranged in a circular shape to mimic a ring. We show by FDTD (Finite-Difference Time-Domain) simulation that a glass substrate removed from this newly created SAA-like structure can increase transmission efficiency by 27.5%. Considering the absorption of the glass substrate is only in the range of 4%-5%, the additional efficiency can actually be attributed to the surface plasmon effect involved in the symmetric nano-structures. Our simulation results were verified by experimental results. The high-aspect ratio microstructures fabricated are also be detailed.

The application of ultrashort pulsed lasers for silicon scribing enables precise control of the ablation depth and generally reduces thermal side effects compared to ns-pulses. However, the formation of periodic holes with a depth of several µm can be observed at the bottom of the scribed trenches. The goal of this study is to investigate the influence of the pulse energy and the scan speed on the depth and average pitch of these holes. For this purpose, a simple model was developed to calculate the number of scans to achieve a specific cutting depth for different pulse energies and scan speeds. Then, wafers with a thickness of 525 μm were scribed to a depth of 50 µm using a fs-laser with a pulse duration of 380 fs and a wavelength of 520 nm. The pulse energy was increased from the minimum pulse energy necessary to achieve a scribing depth of 50 μm,1.6 μJ, up to 8 μJ. In addition, the scan speed was varied between 20 mm/s and 2000 mm/s. Finally, the wafers were broken along the cut and the side walls were investigated with scanning electron microscopy. It was found that the average pitch of the holes decreases and the depth of the holes increases with the pulse energy, while the scan speed has no influence. These findings suggest that the roughness at the trench bottom can be minimized by reducing the pulse energy to the minimum value necessary to achieve the desired cutting depth.

Here we present the holographic fabrication of large area 3D photonic structures using a single reflective optical element (ROE) with a single beam, single exposure process. The ROE consists of a 3D printed plastic support that houses 4, 5, or 6-fold symmetrically arranged reflecting surfaces which redirect a central beam into multiple side beams in an umbrella configuration to be used in multi-beam holography. With a circular polarized beam incident to silicon wafer reflecting surfaces at the Brewster angle, multiple linearly s-polarized side beams are generated. 3D photonic crystal structures of woodpile, Penrose quasi-crystal, and hexagonal symmetry were produced with ROEs that have 4+1, 5+1 and 6+1 beam configurations, respectively. Since the ROE design can be readily changed and implemented for different photonic crystal structures, this fabrication method is more versatile and cost effective than currently comparable single optical methods like prisms and phase masks.

We succeeded in synthesizing antimony (Sb)-doped ZnO microspheres by ablating a ZnO sintered target containing 5 wt% of Sb with a Nd:YAG laser at a fluence of 25 J/cm² in air. The well-spherical ZnO microcrystals with diameters of 1-20 μm were collected on a substrate which was put near the ablation spot. Most of the ZnO microspheres have a crystalline structure. In addition, Raman peak of the Sb-doped ZnO microspheres was shifted toward lower frequency side, indicating substitutional Sb³⁺ at Zn antisite. Room-temperature photoluminescence properties of the microsphere were investigated under 325 nm He-Cd laser or 355 nm Nd:YAG laser excitation. An ultraviolet (UV) emission and lasing in whispering gallery mode were observed from the photoexcited microsphere.