This PDF file contains the front matter associated with SPIE Proceedings Volume 8607, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Quantum dots (QDs) of semiconductors are promising materials for light emission applications due to their size-tunable optoelectronic properties. We present results of direct quantum dot (QD) formation from precursors inside a polymer matrix using laser irradiation. The method is important because it provides a simple means of patterning nanocomposite material within selected regions of a polymer, as required for device design. Several combinations of polymer/precursors films were treated with a picosecond laser at wavelength of 266 nm in order to verify the formation of the QDs inside the polymeric matrix. Precursors for CdS and CdSe QDs were used in experiments. The structural studies of laser-irradiated samples carried out by means of transmission electron microscopy (TEM) showed the QD formation. The size of QDs and the clusters depended on the laser irradiation dose transferred to the film. The QDs were collected to clusters including 10-60 QDs of different size. The mean size of QDs was less than 10nm. The optical analysis carried out by means of UV-VIS and optical microscopy confirmed the formation of the QDs after laser processing. The time-resolved photoluminescence revealed the energy transfer from the organic host to QDs. However, the charge separation was present due to a certain energy level alignment. Modification of the polymer/precursor blends is still required to prevent imbalance of carrier injection to QDs. Photo-luminescent spectroscopy and fluorescence microscopy have revealed that even if the QDs are not emissive, in certain polymer/QDs combinations the PL emission of the polymer is restored after laser treatment.

Zinc oxide (ZnO) nano-crystal is great interest for optoelectronic applications in particular ultraviolet (UV) region such as UV-LEDs, UV-lasers, etc. For the practical optoelectronic applications based on the ZnO nanocrystals, control of nanowire growth direction, shape, density, and position are essentially required. In our study, we introduced a ZnO buffer layer and interference laser irradiation to control the growth position of ZnO nanocrystals. In this presentation, structural and morphological characteristics of periodic ZnO nano-crystals synthesized by the nanoparticle-assisted pulsed laser deposition will be discussed.

We investigated self-propagating sintering of aluminum (Al) nano-particles (NPs) induced by laser ignition on inkderived films. An organic Al-NP ink was used as the precursor. A CW IR fiber laser (1064nm, IPG YLR-50 series with the maximum power of 50W) was used as the sintering source. Electrically-conductive Al wires were successfully processed on glass and silicon substrates, respectively. The sintered Al wire shows lower resistivity (~32μΩ·cm) on the glass substrate and higher resistivity (~150μΩ·cm) on the silicon substrate. N₂ ambient helps to reduce electric resistivity by reducing oxidation. In addition to the sintering procedure and recipe, the sintered wires were characterized using a two-point probe, a scanning electric microscopy and a laser scanning microscopy. The laser heating process was simulated. We also discussed the mechanism of laser ignited sintering.

Maskless patterning of biocompatible sensor chips consisting of a Ta₂O₅/Pt/glass layer system can be realized by ultrashort laser pulse ablation allowing fast and precise structuring. Here, a 650 fs laser at a center wavelength of 1053 nm is used at a peak fluence of 5 J/cm². It was observed, that a greater diameter of the Pt film (400 nm) is ablated when it’s coated with Ta₂O₅ (200 nm) compared to the uncoated Pt. One reason was found in the anti-reflective effect of the Ta₂O₅ layer causing an increase of energy deposition in the material. The underlying physical effects of the ablation reaction are investigated over the whole reaction time ranging temporally from fs to μs by ultrafast pump-probe microscopy. For the direct ablation of the uncoated Pt, results show ultrafast heating and melting after 2 ps, the creation of a gas-liquid mixture and plasma at 10 ps. At around 100 ns the actual ablation takes place indicated by the ejection of small particles. The results for the Ta₂O₅/Pt layer system reveal heating and electron excitation in the Ta₂O₅ layer during the first 2 ps. In the following the spot center behaves identical to the direct ablation of Pt. Here, the Ta₂O₅ is ablated with the Pt. A confined ablation where an additional amount of laser energy is deposited in the layer system or at the layer interface is assumed to take place. In the rim of the spot only the Ta₂O₅ is removed by indirectly-induced ablation at around 35 ns.

For laser micro processing with short and ultra-short pulses the threshold fluence is affected by the incubation and changes with the number of pulses applied. In general the incubation effect is described by a power function including the incubation coefficient S. Beside the threshold fluence also the energy penetration depth is subject to the incubation effect; moreover it is a main cause for the change of the threshold fluence with increasing pulse number.

The behavior of the threshold fluence can be explained by varying absorption (due to changes in the surface reflectivity), chemical changes of the surface (e.g. due to oxidation) or changes in the microstructure of the material whereas the behavior of the energy penetration depth could be explained by the latter two effects but should not be affected by a change in the absorption. To try to distinguish between these three effects a systematic ablation study with 10 ps pulses at 1064nm wavelength on copper and iron under different gases atmospheres and pressures was done.

The results show on the one hand the change of the energy penetration depth is the main cause of the incubation and that on the other hand an adapted model better fits the trend of the threshold fluence and the penetration depth as a function of the number of pulses applied. The influence of the gas (air, oxygen, nitrogen and argon) is only marginal whereas a reduction of the pressure from normal atmosphere down to 50 mbar results in a 25% increase of the maximum removal rate. Induced changes in the microstructure were detected by a high resolution X-ray diffraction analysis on single crystal (111-orientation) copper and iron samples.

For surface and 3D structuring ultra-short pulsed laser systems are used in combination with mechanical axes, whereas the mechanical axes can include electrical motor as well as beam deflecting systems like a galvo scanner. The motion of the axes is synchronized with the clock of the laser pulses, which is usually in the range of 100 kHz and above, by a modification of the electronic axes control. This work shows the scalability of the ablation process up to MHz-regime in relation to surface quality and ablation efficiency. Furthermore the transfer of the machining strategy from a synchronized galvo scanner to a rotating cylinder setup is shown.

Efficient microwelding of glass substrates by irradiation using a double-pulse train of ultrafast laser pulses is demonstrated. The bonding strength of two photosensitive glass substrates welded by double-pulse irradiation was evaluated to be 13.36 MPa, which is approximately 27% greater than that of a sample prepared by conventional irradiation by a single-pulse train. Such an improvement is responsible for individual control of each electron excitation process, i.e., multiphoton ionization or tunneling ionization by the 1st pulse followed by electron heating or avalanche ionization by 2nd pulse. This paper performs characterization of samples prepared by the double-pulse irradiation and then discusses the detailed mechanism for efficient welding.

Femtosecond (fs) laser pulses focused and confined inside the bulk of a material can deposit a volume energy density up to several MJ/cm³ in a sub-micron volume. This creates highly non-equilibrium, hot, dense and short-lived plasmas with conditions favorable for arrangement of atoms into unusual material phases. Singlecrystal silicon was exposed to strong shock waves induced by laser micro-explosion in confined geometry. The conditions of confinement were realized by focusing 170-fs pulses, with the energy up to 2.5 μJ, on a Si surface buried under a 10-μm thick SiO₂-layer formed by oxidation of a Si-wafer. The generated intensity was 10¹⁵ W/cm², well above the threshold for optical breakdown and plasma formation. The shock wave modified areas of the Si crystal were sectioned using a focused-ion beam and characterized with scanning electron microscopy. A void surrounded by a shock-wave-modified Si was observed at the Si/SiO₂ boundary. The results demonstrate that confined micro-explosion opens up new perspectives for studies of high-pressure materials at the laboratory table-top expanding the laser-induced micro-explosion capabilities into the domain of non-transparent materials.

Femtosecond (fs) laser becomes more popular in precise material procesing due to the limited heat affected zone (HAZ) over longer laser pulses. In this paper, micro-hole drilling in ambient air with fs fiber laser at 1030 nm is presented. Micro holes were fabricated in both transparent (polymer and glass), and non-transparent materials (metal and tissue). A scanning electron microscopy is used to investigate the hole quality. Both percusiion drilling and trepanning drilling methods were evaluated and compared. High quality micro holes with no visible micro-cracks were demonstrated. Micro-hole drilling in hard and soft tissues with no collateral thermal damage is observed. This study can be extended to MEMS, microfluidic, and micro surgery applications.

We demonstrated a sensing technique for in-line ablation rate detection using a quantum cascade laser (QCL) under external optical feedback. The design of the QCL-based diagnostic system allowed to monitor the voltage modulation at the laser terminals induced by fast dynamics in the ablation process. Real-time detection of the ablation front velocity as well as in-situ investigations of the surface temperature were provided. Experimental results on fast ablation rates per pulse correlate well with the theoretical prediction. The detection range was demonstrated to be limited only by the QCL-probe emission wavelength, which is scalable up to the THz spectral region.

We report on two-photon excited fluorescence in the oriented Eu³⁺-doped LYB monoclinic crystal under femtosecond laser tight focusing. Due to spatial walk-off, the two polarization modes of the incident femtosecond beam simultaneously provide the independent excitation of two distinct focuses, leading to a single-beam dual-voxel nonlinear excitation of fluorescence below material modification threshold. These observations emphasize on the anisotropy of both two-photon absorption as well as fluorescence emission. They demonstrate the localized control of the nonlinear energy deposit, thanks to the adjustment of both the input power and polarization, by properly balancing the injected energy in each voxel. Such approach should be considered for future direct laser writing of waveguides in propagation directions out of the dielectric axes, so as to optimally cope with the highly probable anisotropy of laser-induced material modification thresholds in these crystals. These results open new ways for further potential developments in direct laser writing as the simultaneous inscription of double-line structures for original waveguides processes.

The field of metamaterials has expanded to include more than four orders of magnitude of the electromagnetic spectrum, ranging from the microwave to the optical. While early metamaterials operated in the microwave region of the spectrum, where standard printed circuit board techniques could be applied, modern designs operating at shorter wavelengths require alternative manufacturing methods, including advanced semiconductor processes. Semiconductor manufacturing methods have proven successful for planar 2D geometries of limited scale. However, these methods are limited by material choice and the range of possible feature sizes, thus hindering the development of metamaterials due to manufacturing challenges. Furthermore, it is difficult to achieve the wide range of scales encountered in modern metamaterial designs with these methods alone. Laser direct-write processes can overcome these challenges while enabling new and exciting fabrication techniques. Laser processes such as micromachining and laser transfer are ideally suited for the development and optimization of 2D and 3D metamaterial structures. These laser processes are advantageous in that they have the ability to both transfer and remove material as well as the capacity to pattern non-traditional surfaces. This paper will present recent advances in laser processing of various types of metamaterial designs.

Integrated hybrid MEMS require new micromanipulation devices in assembly processes. Although absolute forces are restricted optical tweezers are promising tools with unique advantages. Recent developments in beam shaping allow the control of a large number of different particles. Optical manipulation can also be used to assemble tiny structures by a generative process. Any type of particle, primarily coated with high-affinity biomolecules, can be applied as building blocks to form complex structures. By moving the particle into the requested orientation by holographic optical tweezers complex parts become possible. Also, shape-complimentary preforms can be fabricated with 2-photon-polymerization (2PP) and utilized to assemble the desired structure. Finally, microvalves and motors in lab-on-a-chip systems can be optically fabricated and also driven by optical forces.

A holographic laser machining can improve the processing efficiency. In the method, multiple light spots are generated at the processing positions by focusing a spatially phase modulated laser beam with a spatial light modulator. When this method is applied to bulk-laser machining, the accuracy of focusing positions is sometimes reduced because of the distortion of light focusing. In this paper, we present two calculation method of a phase hologram for reducing the distortion of light focusing. One method is based on the iterative Fourier transform method. In this method, the distortion of light focusing was reduced by fixing phase in light spots in the iterative process. The other is based on the optimal rotation angle method. In this method, the evaluation function was modified to make the light intensity at the positions of phase jump zero. In both two methods, we succeed to improve the quality of light spots. In addition, we show the application of these methods to writing of optical waveguides inside glasses.

The paper presents results obtained in a comparative study of laser irradiation of tungsten powder surfaces using a continuous wave fiber laser and a high repetition rate femtosecond laser. Depending on the energy input per unit length different melt structures have been produced. In general, if the same average laser power level was applied the structures show the same appearance independent from the laser source. But there was both a little higher degree of initial fusing and cross-linking along the processed path when the powder surface was irradiated with ultrashort pulses. Further, with increasing laser intensity a change in structure formation as well as a broadening of the laser processed path has been occurred, although the energy input per unit length remains constant. However, accumulation of slab-like structures, which was previously observed in high-intense ultrashort pulse laser irradiation, has been become more pronounced in cw laser irradiation above a certain number of consecutive scans. Moreover, characteristic effects, such as formation of ripples and nanomelt structures appearing in ultrashort pulse laser processing have been not detected in cw laser irradiation.

Liquids laser printing has been usually addressed through laser-induced forward transfer, a technique that allows the deposition of microdroplets with good resolution and control. However, it presents a significant drawback that can compromise its future industrial implementation: the need for the preparation of the liquid to be printed in thin film form. Such constraint results especially detrimental when very high degrees of resolution need to be achieved. In order to overcome the problem, we have recently shown that in the case of solutions transparent or weakly absorbing to the laser radiation, liquid printing is possible directly from the liquid contained in a reservoir, without the requirement of thin film preparation. The principle of operation of the film-free laser printing technique is the tight focusing of ultrashort laser pulses underneath the free surface of a liquid. Subsurface absorption leads to the formation of a cavitation bubble through optical breakdown, and the subsequent bubble expansion displaces some liquid towards the substrate, where the pattern is formed. Though the feasibility of the technique for microdroplets printing has already been proved, there is not much insight yet in the mechanisms of liquid ejection and transport. In this work we investigate the mechanisms of liquid printing during film-free laser forward printing. The study, essential for the optimization of the technique, reveals that the process is complex: the bubble expansion-collapse cycle results in the formation of two consecutive jets which display completely different dynamics, and which behavior is strongly dependent on the laser pulse energy density.

The development of organic electronic requires a non contact digital printing process. The European funded e-LIFT project investigated the possibility of using the Laser Induced Forward Transfer (LIFT) technique to address this field of applications. This process has been optimized for the deposition of functional organic and inorganic materials in liquid and solid phase, and a set of polymer dynamic release layer (DRL) has been developed to allow a safe transfer of a large range of thin films. Then, some specific applications related to the development of heterogeneous integration in organic electronics have been addressed. We demonstrated the ability of LIFT process to print thin film of organic semiconductor and to realize Organic Thin Film Transistors (OTFT) with mobilities as high as 4 10^-2 cm².V^-1.s^-1 and I_on/I_off ratio of 2.8 10⁵. Polymer Light Emitting Diodes (PLED) have been laser printed by transferring in a single step process a stack of thin films, leading to the fabrication of red, blue green PLEDs with luminance ranging from 145 cd.m^-2 to 540 cd.m^-2. Then, chemical sensors and biosensors have been fabricated by printing polymers and proteins on Surface Acoustic Wave (SAW) devices. The ability of LIFT to transfer several sensing elements on a same device with high resolution allows improving the selectivity of these sensors and biosensors. Gas sensors based on the deposition of semiconducting oxide (SnO₂) and biosensors for the detection of herbicides relying on the printing of proteins have also been realized and their performances overcome those of commercial devices. At last, we successfully laser-printed thermoelectric materials and realized microgenerators for energy harvesting applications.

Rapid developments in organic electronics promise low cost devices for applications such as OLED, organic transistors and organic photovoltaics on large-area glass or flexible substrates in the near future. The technology is very attractive as most device layers can be solution printed. But when directly patterned deposition is impossible, a post-patterning step is required and laser processing is gradually emerging as a key-enabling tool. DPSS lasers offer several advantages including maskless, non-contact, dry patterning, but also scalable large area processing, well suited to roll-to-roll manufacturing at μm resolutions. However, very few reports discuss in detail the merits of DPSS laser patterning technology, especially on flexible substrates. This paper describes the potential of ultrafast DPSS laser technology for OLED fabrication on foil and, specifically, picosecond laser ablation of PEDOT:PSS on multilayered barrier/foil or metal grids aimed as a synthetic alternative to inorganic transparent conductive electrodes. Key requirements include: (a) the complete removal of PEDOT layers without residue, (b) the complete absence of surface contamination from redeposited laser debris to avoid short circuiting and (c) no loss in performance of from laser exposure. We will demonstrate that with careful optimisation and appropriate choice of ultrafast laser, the above criteria can be fulfilled. A suitable process window exists resulting in clean laser structuring without damage to the underlying heat sensitive barrier layers whilst also containing laser debris. A low temperature ablation most likely proceeds via a stress-assisted (film fracture and ejection) process as opposed to vaporisation or other phase change commonly encountered with longer pulse lasers.

Cost-effective laser patterning of indium tin oxide (ITO) thin film coated on flexible polyethylene terephthalate (PET) film substrate for touch panel was studied. The target scribing width was set to the order of 10 μm in order to examine issues involved with higher feature resolution. Picosecond-pulsed laser and Q-switched nanosecond-pulsed laser at the wavelength of 532nm were applied for the comparison of laser patterning in picosecond and nanosecond regimes. While relatively superior scribing quality was achieved by picosecond laser, 532 nm wavelength showed a limitation due to weaker absorption in ITO film. In order to seek for cost-effective solution for high resolution ITO scribing, nanosecond laser pulses were applied and performance of 532nm and 1064nm wavelengths were compared. 1064nm wavelength shows relatively better scribing quality due to the higher absorption ratio in ITO film, yet at noticeable substrate damage. Through single pulse based scribing experiments, we inspected that reduced pulse overlapping is preferred in order to minimize the substrate damage during line patterning.

We report on the laser cutting of carbon fiber reinforced plastics (CFRP) with a cw IR fiber laser (average power: 1kW). CFRP is a high strength composite material with a lightweight, and is increasingly being used various applications. A well-defined cutting of CFRP which were free of debris and thermal-damages around the grooves, were performed by the laser irradiation with a fast beam galvanometer scanning on a multiple-scan-pass method.

The LGP (Light guide plate) plays a key role of the backlight in LCD module. It determines the efficiency and uniformity of the whole backlight unit (BLU). With decreasing thickness in panel system and reduced quantity of LEDs, the Hotspot issue becomes more and more serious. We proposed a virtual light field of LEDs embedded inside the LGP for non-sequential ray-tracing. Two semi-analytical formulations are conducted to optimize the micro-dots’ distribution when LGP is with mirrored or corrugated entrance plane. The ultra-slim LGPs fabricated by solid-state laser and diamond-ruling machine show excellent elimination of the Hotspot phenomenon.

Extensive research in micro/nanoscale surface engineering has developed a variety of energy applications including improvement of light trapping performance in solar cells, and increased surfaced area on electrodes in batteries or fuel cells applications with extended life time. In this study, we are aiming to the evaluation of a cost effective surface texturing method based on rapid scanning of nanosecond laser pulses. In contrast to conventional laser-assisted methods, we have achieved highly uniform and controllable texturing means over arbitrary scanning area of semiconductor and metallic surfaces.

There is increasing demand for functional polymeric optical coatings for plastic substrates. In the case of anti-reflective (AR) coatings, this is challenging because polymers exhibit a relatively narrow range of refractive indices. We synthesized a four-layer AR stack using hybrid polymer:nanoparticle materials deposited by resonant infrared matrixassisted pulsed laser evaporation (RIR-MAPLE). An Er:YAG laser ablated frozen solutions of a high-index composite containing TiO2 nanoparticles and PMMA, alternating with a low-index solution of PMMA. The optimized AR coatings, with thicknesses calculated using commercial software, yielded a coating for polycarbonate with relative transmission over 94%, scattering less than 5% and a reflection coefficient below 0.8% across the visible range.

While utilization of renewable solar energy by converting to electricity via photovoltaic (PV) solar cells is one promising route to meet urgent energy needs without involving fossil fuel consumption or carbon dioxide emission, the challenge lies on reducing the cost per watt to compete with traditional fossil fuel technology. To this end, developing low cost PV manufacturing technologies at improved manufacturing and device efficiencies is primary challenge to ensure that solar energy is a viable and economic source for power needs. In this paper, recent efforts on short pulsed laser scribing processes of CIGS (Copper Indium Gallium Diselenide) thin film solar cells will be demonstrated. High repetition rate (~ 100 kHz) picosecond laser based results are compared with those by nanosecond laser. Advantages and limitations of picosecond laser scribing process will be discussed, and a tentative solution based on cost-effective nanosecond lasers will be proposed. A further improved scribing quality and accuracy will be also attempted by gas injection scheme.

New developments in the thin film solar market continue the trend towards solar modules with higher energy conversion while at the same time, reducing significantly manufacturing costs. Especially thin film technologies based on Cadmiumtellurid (CdTe) or Cu(In,Ga)(S,Se)₂ (CIGS) seem to be suited to improve the energy conversion and hence, take over larger market shares. With this work, we present our latest achievements towards a CIGS all laser scribing process with the emphasis on structuring the absorber layer and its implications to the production. While P1 laser scribing through the substrate is already implemented in production today a variety of different approaches, like lift-off, ablation, or remelting are possible for the P2 process where commonly a mechanical process is state of the art. One challenge which the P2 and P3 processes face is the layer side processing. Therefore a thorough investigation has been conducted including different laser wavelengths (355 nm to 1550 nm), pulse durations (10 ps to 100 ns), and beam shaping to find the best possible solution for each scribing process. Optimization took place utilizing not only resistance measurement and optical microscopy but also LSM, REM, EDX, EL, and Lock-In Thermography. Combining the best results of each scribing process and using a high speed, high accuracy motion system a functional lab size module has been produced with a reduced dead zone of below 200 m. In an outlook, a way is presented on how to take the lab results into a productive system and place it in a manufacturing environment.

This work presents an effectively implemented calibrated polarization-independent Fresnel attenuator of laser radiation power built on the basis of two Dove prisms. A method of the attenuator’s alignment with a laser beam axis as well as of determining the main axes of laser radiation polarization is herein demonstrated. It is shown and experimentally proved that using model calculations the prisms’ manufacturing and assembly imperfections can be compensated by the attenuator’s rotation by certain angles and a corresponding change of the system’s total reflection coefficient.

Knowing the optical properties of metals in solid and liquid phase is important for understanding and optimizing material processing. But it is difficult to find reliable data, especially for the wavelength range in the near-infrared. Further there are several approaches of extending the Drude-model for optical properties of metals including temperature dependency and intra-band absorption, which can describe the qualitatively behavior of optical properties as a function of temperature and wavelength. Although these extended models can predict accurately the optical properties for some specific metals and wavelengths, in general they fail to predict accurate values. Comparing our own experimental results of gold and silver in the solid and liquid phase at near-infrared with extended Drude-models has revealed that even a combined extended Drude-model taking temperature dependency, anomalous skin effect and intra-band absorption into account, cannot predict the optical properties accurately. In general the temperature dependency of the optical properties of metals is much weaker than predicted by the various models. Additionally analyzing the refractive index and absorption coefficient of metals at 1.06μm and 10.6μm has shown a difference of approximately a factor of 10 between 1.06μm and 10.6μm causing a sharp absorption peak at 10.6μm compared to a broaden peak at 1.06μm. This factor of 10 is much larger than the difference of the optical properties between the solid and the liquid phase and has a great influence on the laser energy distribution absorbed in the metal during laser processing.

As industry of PCB (Printed Circuit Board) and display growing, this industry requires an increasingly high-precision quality so current cutting process in industry is preferred laser machining than mechanical machining. Now, laser machining is used almost “step and repeat” method in large area, but this method has a problem such as cutting quality in the continuity of edge parts, cutting speed and low productivity. To solve these problems in large area, on-the-fly (stagescanner synchronized system) is gradually increasing. On-the-fly technology is able to process large area with high speed because of stage-scanner synchronized moving. We designed laser-based high precision system with on-the-fly. In this system, we used UV nano-second pulse laser, power controller and scanner with telecentric f-theta lens. The power controller is consisted of HWP(Half Wave Plate), thin film plate polarizer, photo diode, micro step motor and control board. Laser power is possible to monitor real-time and adjust precision power by using power controller. Using this machine, we tested cutting of large area coverlay and sheet type large area PCB by applying on-the-fly. As a result, our developed machine is possible to process large area without the problem of the continuity of edge parts and by high cutting speed than competitor about coverlay.

In the field of ablative-based material processing there is a desire to use short pulse width (subns) laser sources. If the pulse width is too long <10 ns the processing is fast, but crude. If the pulse width is too short <10 ps the processing is precise, but slow. In an effort to balance the process fidelity with material removal rate, a unique TEM₀₀ mode quality sub-ns (~0.5 ns nominal pulse width) laser was developed.

This work reports femtosecond laser based fabrication of long period fiber gratings (LPFG). Index modulation in the core of single mode fiber (SMF) is written employing femtosecond pulse filamentation technique. Highly repeatable filamentary voids written in line-by-line femtosecond laser inscription technique enables steady and noise free growth of LPFGs. The sharp transmission valley (with a narrow full width at half maximum of 5 nm) of long period grating offers better resolution for refractive index (RI) measurement of a solution. The LPFGs inscribed by femtosecond laser radiation show RI sensing sensitivity of 29.199 nm/RIU which is three times higher than the sensitivity of LPFGs written by UV radiation (sensitivity: 11.179 nm/RIU). The position of transmission dip of a grating can be tailored relatively easily simply by varying the period of index modulation.

Laser micromachining is one of many laser material processing technologies employed in scientific research and engineering applications. It involves the deposition of photon energy and the material interaction. The intense photothermal energy is transported into the target material causing melting and evaporation. The material is removed layer by layer by melting and flowing away or by direct vaporization / ablation. It is due to the focused small spot size that the laser micromachining can remove material in small quantity at a time, thus precise control of geometrical dimension is possible. In this work, a nanosecond pulsed Nd:Yttrium-Aluminum-Garnet (Nd:YAG) laser was employed to generate relatively long notch of different dimensions (25.4 mm-length × 0.1 mm-width × 0.051/0.102/0.152 mmdepth) on Ti-3Al-2.5V seamless tubes for fatigue life study. Cyclic hydraulic impulse pressure test was conducted to find out the fatigue limits of the titanium tube containing the laser micromachined notch. The results of fatigue lives, crack profile and pattern of crack propagation are presented and discussed in this paper. Scanning electron microscopy was employed to characterize the fatigue crack profile and the laser micronotch. The capability of generating sharper notch root and consistent pre-crack on the surface of materials makes nanosecond pulsed Nd:YAG laser a great choice in preparing for fatigue test samples for crack growth life study.