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We investigated a simple and productive micromachining method of silica glass by ablation using a TEA CO laser (10.6 μm) with a spatial resolution down to sub-wavelength scale. The silica glass was irradiated by the TEA CO laser light through a copper grid mask with square apertures of 20×20 μm attached to the silica glass surface. After the irradiation, circular holes with a diameter of several μm were formed on the silica glass surface at the centers of the apertures due to the Fresnel diffraction effect. The minimum diameter of the holes was 3.4 μm. The characteristics of the micromachining are discussed based on the electric field distributions of the CO laser light under the mask using a three-dimensional full-wave electromagnetic field simulation. [ABSTRACT FROM AUTHOR]

Abstract: Microstructures with well-defined micropatterns were fabricated on the surfaces of silica glass using a laser-induced backside wet etching (LIBWE) method by diode-pumped solid state (DPSS) UV laser at the repetition rate of 10kHz. For a demonstration of flexible rapid prototyping as mask-less exposure system, the focused laser beam was directed to the sample by galvanometer-based point scanning system. Additionally, a diagnostics study of plume propagation in the ablated products of toluene solid film was carried out with an intensified CCD (ICCD) camera. [Copyright &y& Elsevier]

Transient processes of laser ablation of a highly laser-absorbing liquid, toluene, were investigated by directly measuring (by using a fast-response pressure gauge) the transient pressure caused by toluene ablation under KrF laser irradiation . The results were compared with time-resolved images . The peak pressure P due to a shock wave decreased slowly with increasing distance d for d=100-1000 µm:P?d-0.33. By extrapolating P to d=8.9 µm, the optical penetration depth of toluene at ?=248 nm, the estimated initial pressure due to toluene ablation was 65 MPa at 1.0 J cm-2 pulse-1. The estimated initial pressure increased linearly with the fluence. These results help clarify the mechanism of laser-induced backside wet etching. [ABSTRACT FROM AUTHOR]

By a laser-induced backside wet etching method using a pyrene/acetone solution, a fused silica plate was etched upon irradiation with a conventional XeCl excimer laser. The etch rate was about 50% lower than that obtained with a KrF excimer laser under the same experimental conditions. The threshold fluence for etching was estimated to be below 0.5 J cm−2 and a typical etch rate was around 10 nm pulse−1 at a fluence of 1 J cm−2. After producing the sample having the 10 μm lines and space by irradiation with the first 200 pulses, the second 400 pulses were irradiated to the target sample rotated at right angle. As a result, a square dotted pattern was given without damages for the first etched pattern. Micrographs of the etched surfaces show that this process is a remarkably gentle process free from crack and debris, and favorable for microcrack-free etching of transparent materials. [Copyright &y& Elsevier]

An organosilicon compound, hexamethylcyclotrisilazane (HMCTS), was photolyzed in a solid film at 84 K with an ArF excimer laser. A polymeric film was prepared as a result of polymerization and/or crosslinking using a reactive species such as 1-(methylsilyl)methanimine, generated by photolysis. At room temperature in air, the film changed into a polymer having siloxane units. However, fragments generated by laser irradiation of HMCTS in the frozen film made a similar polymer film having a siloxane structure on a PVA film in air. The polymeric film with siloxane units prepared by the cryogenic laser ablation method displayed hydrophobic properties. [ABSTRACT FROM AUTHOR]

Abstract. KrF excimer-laser ablation of sintered-powder polytetrafluoroethylene (PTFE) targets is used for the deposition of high-quality PTFE films on metallic microstructures and metal backplates for electroacoustic applications. The films are found to be highly crystalline, consisting of large spherulites with diameters up to 1 mm. X-ray photoelectron spectroscopy of the films revealed the chemical similarity of press-sinter target pulsed-laser-deposited films with bulk PTFE. Negatively charged PTFE films on stainless steel backplates exhibit an exceptional charge stability with practically no decrease of the surface potential up to 225 Celsius in open-circuit thermally stimulated discharge. [ABSTRACT FROM AUTHOR]

Abstract. Ablation of pentafluorophenylazide (FPA) in an Ar matrix at 8-10K was carried out upon irradiation with ns-pulsed UV lasers in a vacuum. The plume of ablated products was monitored by a time-resolved imaging/spectroscopic technique using a gated and intensified CCD camera system. A large amount of pentafluorophenylnitrene (FPN) having a high kinetic energy (Is approximately equal to 6 eV) was ejected as fragments from the matrix film during ablation. A quantitative formation of triplet FPN from the photolysis of the FPA was observed by spectroscopic measurements in the IR and UV-visible regions, and was confirmed by a theoretical IR spectrum calculated according to density functional theory. A FPN beam is useful for chemical surface modification of organic materials. such as aromatic polyester and alkylthiol. A surface analysis of these materials by X-ray photoelectron spectroscopy and Fourier transform infrared reflection absorption spectroscopy showed that the FPN was immobilized onto the surface through chemical bonds. This technique for the chemical surface modification of materials is made possible by a pulsed beam of reactive fragments with a high density in the laser ablation process. [ABSTRACT FROM AUTHOR]

Abstract. We have applied laser ionization time-of-flight (TOF) mass spectrometry to ablation of polysulfone (PS) with 266 nm laser light at fluences of 20-60 mJ/cm[sup 2]. Major peaks were assigned to direct fragments and recombination products ejected from the PS surface. The arrival profiles of these ablation products varied from product to product and were fitted by using a shifted Maxwell-Boltzmann distribution with a center-of-mass flight velocity [(1.4- 5.6) x 10[sup 5] cm/s] and a Knudsen layer temperature (350-3810K). Two types of ablation products, whose velocities and temperatures showed different dependences on laser fluence, were found to exist. Dynamical aspects in the decomposition of the polymer chain, the ejection of various fragments, and their expansion am discussed on the basis of a photothermal ablation model, where a heated surface layer with a temperature gradient along its depth plays an important role. [ABSTRACT FROM AUTHOR]

Initial stage of F2 laser ablation of LiCaAlF6 single crystal was investigated for clarifying the possibility of applying this wide bandgap fluoride crystal to vacuum ultraviolet (VUV) optical components. The ablation threshold, determined by the appearance of line emission from ablated species, was approximately 2 J cm-2pulse-1, similar to that of VUV grade CaF2 single crystal. The laser-induced damage on the front surface of LiCaAlF6 was faint, though adhesion of aggregated particulates of several microns was observed. [ABSTRACT FROM AUTHOR]

To clarify the initial stage of laser-induced backside wet etching, we directly measured transient pressure upon laser ablation of toluene under KrF excimer laser irradiation by using a fast-response pressure gauge. The propagation time of the pressure peak to the gauge agreed well with the time for the shock wave to reach the gauge on time-resolved images. The peak pressure P decreased slowly with increasing distance d: P=30.4 MPa for d=100 μm to P=11.1 MPa for d=1000 μm at a fluence F=1.0 J cm-2 pulse-1. The initial pressure, estimated to be of the order of 10–200 MPa, impinges on a transparent plate and contributes to the etching. [ABSTRACT FROM AUTHOR]

Abstract. We have developed a one-step technique to fabricate a well-defined pattern of lines and spaces in fused silica with micro-sized features, using laser-induced backside wet etching (LIBWE). The etch rate ranged from 5 to 25 nm/pulse with KrF laser irradiation from 400 to 1300mJ/cm[sup 2] and an acetone solution containing pyrene at a concentration of 0.4 mol/dm[sup 3]. The threshold fluence was 240 mJ/cm[sup 2], which is about one-fortieth lower than that obtained with conventional KrF laser ablation. [ABSTRACT FROM AUTHOR]

Abstract. Ablation of pentafluorophenylazide (FPA) on an Ag plate at 10 K was carried out upon irradiation with a ns-pulsed UV laser at 248 nm in vacuum. The plume of ablated products was monitored by a time-resolved imaging/spectroscopic technique using a time-gated and intensified CCD camera system. The emission spectrum of the plume at gate times of between 1.0 and 2.0 micro s after the laser irradiation was attributed to blackbody radiation. The blackbody temperature upon irradiation at 100 mJ cm[sup -2] pulse[sup -1] was estimated to be 2900 K. This high-temperature emission is explained by an exothermic reaction of FPA photolysis, which was supported by a theoretical calculation of formation enthalpy based on density functional theory. [ABSTRACT FROM AUTHOR]

Abstract. The KrF laser ablation of polyarylsulfone (PAS) was investigated for fluences between 90 and 200 mJ/cm[sup 2]. Neutral fragments were probed using laser post ionization (193 nm) time-of-flight (TOF) mass spectrometry. Decomposition of PAS was found to occur mainly through scission of C-S and C-O bonds as well as via decomposition of the phenylene rings in the chain. The dependencies of both the flight velocities and the Knudsen layer temperature of the fragments on fluence suggest that PAS ablation is a photothermal process. In contrast, the high average translational energies (up to a few tens of eV) indicate the existence of a non-thermal component in the process. In terms of the plume dynamics, the fitting of the arrival profiles of the fragments with a shifted Maxwell-Boltzmann distribution over the full fluence range indicates the existence of a collision during the adiabatic expansion process. [ABSTRACT FROM AUTHOR]

KrF excimer laser ablation of iron disilicide in the α phase (α-FeSi2) has been investigated using time-of-flight (TOF) mass spectroscopy to characterize the dependence of ejected neutrals and native positive ions on laser fluence. The TOF mass spectra showed that the ejection behavior was classified into three parts at low, moderate and high fluence ranges. At laser fluences below 0.7 J/cm2, the presence of only Si, Fe and Si2 neutrals was confirmed; the arrival profile of Si atoms is well described by a Maxwell–Boltzmann (MB) distribution with a translational velocity of 1.6×103 m/s, corresponding to a kinetic energy of 0.35 eV, and a target surface temperature of 4.0×103 K, indicating a thermal emission of these neutral species. With increasing the fluence, nascent positive ions, such as singly- or doubly-charged Si and Fe ions appeared; the arrival profiles of these ions are observed to fit a shifted MB distribution. Their kinetic energies range from several eV at moderate fluences to over 100 eV at high fluences up to 2.5 J/cm2. These high kinetic energies cannot be explained in terms of the FeSi2 target surface reaching a temperature that would produce such energetic ions upon ablation, suggesting the ion acceleration in a dense plasma plume. [Copyright &y& Elsevier]

We have investigated time evolution of the plume produced during laser ablation of ZnO under ArF-excimer-laser irradiation in He atmosphere. The plume luminescence is mainly due to excited Zn atoms. The plume propagates straightforwardly within 1 μs after ablation, and then it expands and forms an anchor-like shape due to the plasma confinement by the surrounding He gas. After the disappearance of the plume luminescence at high He pressure, a second excitation with a XeCl-excimer-laser causes a luminescence that can be explained in terms of condensation and formation of oxygen molecules and ZnO nanoparticles in the plume. [Copyright &y& Elsevier]