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Effects of thermal post treatment and of thickness of the initial gold film coated the silicate glass surface, on localized surface plasmon resonance (SPR) of gold nanoparticles formed in glass by UV laser irradiation were studied to develop effective technique for production of gold nanoparticles and their arrays with required and stable characteristics of SPR. Optical spectra of the obtained Au/glass samples showed that SPR of gold nanoparticles formed by irradiation of glasses sputter coated with gold films of thickness 6–10 nm depends of T-treatment, while irradiation of glass coated with gold film ∼70 nm leads to SPR stable of temperature. The origin of such dependences was studied by the structural analysis of gold nanoparticles in Au/glass samples before and after thermal treatment using XRD, EXAFS methods, TEM-EDX images and direct calculations of optical spectra. It was revealed that the changes or stability of SPR parameters under thermal post-treatment of Au/glass samples depend respectively of the presence or absence of tin atoms in the near-surface region (shell) of the gold particles. Thus, if tin atoms are presented in the shell of gold particles (as in “as prepared” Au/glass samples initially coated with gold films of 6–10 nm) then the leave of tin atoms from the particle's volume during the heating leads to partial dissolution of the particles shell and consequently, to decreasing of the particles size, which in turn leads to the observed changes in SPR. The most probable explanation of the presence of tin atoms in the shell of gold particles formed by irradiation of samples initially coated with gold films of thickness 6–10 nm and their absence in the case of sample with film ∼70 nm was proposed, basing on the difference in the effects of the first laser pulse actions on these films on the tin-bath side of the glass samples. The sizes of coherent scattering region in gold nanoparticles before and after thermal treatment of Au/glass samples were determined and the dependence of these sizes upon the thickness of the gold film coating the sample's surface before laser irradiation was revealed.

We have completed modeling of a laser pulse influence on a gold target. We have applied a hybrid atomistic-continuum model to analyze the physical mechanisms responsible for the process of nanostructuring. The model combines the advantages of Molecular Dynamics and Two Temperature Model. We have carried out a direct comparison of the modeling results and experimental data on nano-modification due to a single ps laser pulse at the energy densities significantly exceeding the melting threshold. The experimental data is obtained due to a laser pulse irradiation at the wavelength of 248 nm and duration of 1.6 ps. The mask projection (diffraction grating) creates the sinusoidal intensity distribution on a gold surface with periods of 270 nm, 350 nm, and 500 nm. The experimental data and modeling results have demonstrated a good match subject to complex interrelations between a fast material response to the laser excitation, generation of crystal defects, phase transitions and hydrodynamic motion of matter under condition of strong laser-induced non-equilibrium. The performed work confirms the proposed approach as a powerful tool for revealing the physical mechanisms underlying the process of nanostructuring of metal surfaces. Detailed understanding of the dynamics of these processes gives the possibility for designing the topology of functional surfaces on nano- and micro-scales.

Diffractive phase elements (DPE), consisting of a patterned UV-transparent layer on a UV-transparent substrate, were fabricated by three steps. A UV-absorbing SiO x -coating (x < 2) with a thickness matching to the required phase delay was deposited on a fused silica substrate. The coating was removed on a pixel array corresponding to a calculated two-dimensional quantized phase function (DPE-design). By a thermal annealing process the SiO x -coating was oxidised to UV-transparent SiO 2 , resulting in a UV-grade surface relief element.

Two different highly sensitive and fast but low-cost instruments for fluorescence measurements on nanotiter plates or other high density sample arrays are presented. Both instruments use 635 nm diode lasers for the detection of Cy5 fluorescence. In the first device all cavities of the nanotiter plate are illuminated simultaneously and the fluorescence is detected spatially resolved by a charge-coupled device camera within a few seconds. The second system uses an on-chip microscanner for the sequential illumination of the samples and the fluorescence is detected by a simple photomultiplier tube. Both instruments have originally been developed for environmental analysis by immunochemical labeling but they can also be used for other medical and biological purposes where analyte concentrations have to be determined.

Nanofibers made from organic molecules such as para-hexaphenyl allow guiding of electromagnetic waves. Since they possess nanometric widths and heights but macroscopic lengths they represent the smallest possible optical waveguides. Recently, gain enhancement has been observed, pointing to possible applications as nanolasers. Owing to their self assembly growth mode on mica substrates the nanofibers posses well-defined morphology. In order to implement these aggregates into new optical devices or to enhance feedback and thus build up a resonator structure a defined cutting of the end faces is necessary. This article presents results from the first experimental studies in this direction. Irradiation with UV laser pulses of 193 nm at a fluence of 100 mJ/cm 2 removes the fibers completely without damaging the substrate. In addition, the fibers can be cut in any orientation relative to their long axes. The quality of the ablation process in terms of readsorbed debris and steepness of cutting is investigated by atomic force and scanning electron as well as fluorescence microscopy.

Laser ablation of polyimide (PI) and polymethyl-methacrylate (PMMA) at 248 nm with pulse lengths τ ranging from 200 fs to 200 ns was investigated. The measured ablation rates increase towards long and very short pulses and show minima for pulse lengths of about 5 ps (PMMA) or 50 ps (PI). Measurements of the reflected and transmitted portion of the ablating laser pulse give additional information about the factors influencing the ablation rates. The minimum of the ablation rate coinciding with a maximum of the reflectance of the ablating pulse can be explained by a dynamic plasma reflection model: A fast build up of a dense plasma is followed by high obscuration for a brief transition time and self-regulating opacity for the rest of the pulse. This model of plasma mediated ablation leads to a τ 1/4 -dependence of the ablation rate at fixed fluence, which fits very well to the measured data in the range above 50 ps. In the long pulse regime (20 ns to 200 ns), the attenuation of the ablating laser pulse by the expanding ablation plume was investigated by using a small sensing hole in the sample within the ablation spot. In combination with ablation rate measurements with varying laser spot size, these results lead to the conclusion, that the three dimensional plume expansion determines the fraction of the laser pulse actually reaching the sample. Concerning plasma and plume effects at high fluence irradiation, three effects influence the ablation behavior on different time scales: The time constant for plasma formation is important on the fs-ps time scale, self regulating plasma on the ps-ns time scale, three dimensional plume expansion on the ns-µs time scale.

Surface treatment of metals and other materials is studied using sub-picosecond laser pulses at 248 nm. The advantage of the combination of femtosecond pulse durations with ultraviolet wavelengths is pointed out. Full utilization of the specific pulse parameters for nano-scale material processing is demonstrated. Imaging techniques combined with diffractive optical elements are exploited for the generation of two dimensional periodic structures. Superior quality and feature sizes below 100 nm are achieved. The ultra-short pulse UV laser system applied for surface texturing comprises a Ti:Sapphire front-end system and a specially developed excimer amplifier module generating 300 fs pulses at 248 nm with an average power of ~10 W. The excimer module operating at 300 Hz together with a newly introduced beam smoothing technique allows high precision texturing of large surfaces opening up new possibilities in industrial applications.

F 2 -laser ablation at 157 nm was used for generating sub-micron surface relief structures on fused silica to define binary diffractive phase elements (DPE). A pattern array of 128 x 128 pixels was excised using the F2 laser in combination with a high resolution processing system comprising of CaF 2 beam-homogenization optics and a high-resolution Schwarzschild reflective objective. A square projection mask provided precise excisions in less than 10 x 10 μm 2 spots, having sub-μm depths that were controlled by the laser fluence and the number of laser pulses to provide for the required phase delay between ablated and non-ablated pixels. Thus a diffractive phase element (DPE) optimized for first order in the UV spectral range was made. A four-level DPE design computed by the Iterative Fourier Transform Algorithm (IFTA) will be described for generating an arbitrary irradiation pattern without the point symmetry of a two level design.

Excimer laser ablation at 193 nm is used for the generation of a surface relief structure on fused silica with the aim to fabricate diffractive optical phase elements to be applied for efficient laser materials processing. Though there are several problems to achieve high aspect ratio material removal at this laser wavelength (193 nm) in a scarcely absorbing material (fused silica), ablation of sub-μm depth, as it is needed to generate the appropriate phase delays of diffractive phase elements (DPE) for UV-applications, is possible without cracking. Applying a machining process corresponding to a bitmapped DPE design generated by an Iterative Fourier Transform Algorithm (IFTA), the fused silica surface is patterned on a 128 x 128 pixel 2 area with a pixel size of 12.5 x 12.5 μm 2 . The step height of this two level DPE has to be adapted to the combination of the wavelength, at which the element will be applied, and the refractive indices of the DPE-material and the environment. The example DPE is designed as a 10 x 10 focus raster generator for a UV-femtosecond laser operating at 248 nm. Using this DPE in combination with a 25x Schwarzschild objective, the parallel drilling of micron sized holes in stainless steel and other metals is demonstrated.

Submicron surface-relief gratings were fabricated on fused silica by laser ablation with nanosecond (ns) pulses from a high-resolution F 2 -laser processing station. The grating relief was generated by imaging a transmission amplitude grating with a Schwarzschild objective of 25x demagnification. The chrome-coated CaF 2 mask had been structured by laser ablation at 193 nm to form a line and space pattern of 20-μm period. The F 2 -laser generated gratings on fused silica were characterized by SEM, AFM and diffraction of a HeNe laser beam, yielding a grating period of 830 nm and a corrugation depth of 250 nm. Surface-relief gratings on optical materials are required for various applications such as grating demultiplexers for telecommunication components, light couplers for planar optical waveguides, Bragg reflectors, or alignment grooves for liquid crystals. Laser ablation is a rapid and flexible method to generate custom grating designs on a variety of materials.

Surface treatment of stainless steel and other metals is presented using subpicosecond laser pulses at 248 nm. Applying diffractive optical masks combined with a reflective imaging system sub-micron size features are generated on the sample surface. During the experiments different types of diffractive elements are used. The imaging properties of an amplitude mask consisting of crossed lines and a 2 level diffractive phase element (DPE) are compared to obtain micro hole arrays. Ablated structures with diameters between 300 nm and 1,5 μm are presented. The ultrashort pulse UV laser system applied for surface texturing comprises a Ti:Sapphire front end system and a specially developed excimer amplifier module generating 300 fs pulses at 248 nm with an average power of close to 10 W. Using the above mentioned diffractive optical elements and the newly developed excimer module operating at 300 Hz allows high precision texturing of large surfaces opening up new possibilities in industrial applications.

Excimer laser ablation is a versatile method to generate three dimensional microstructured devices for mechanics, fluidics and optics. Especially, if in one dimension the structure is predefined by a layer design, and the other two dimensions are defined in the layer ablation process by mask projection, very precise structure definition in three dimensions and ablated surfaces with optical quality can be achieved. Patterning optical layers or layer stacks, a variety of applications is possible. As examples the fabrication of dielectric masks and diffractive optical elements and the performance of these elements in shaping excimer laser beams are demonstrated.

The F2-laser Nano fabrication Facility at the University of Toronto delivers high-fluence 157-nm radiation at high resolution to micro fabricate high-finesse silica-based optical components. The 7.9-eV photons drive strong material interactions near the band-edge states of fused silica and related glasses that help avoid microcrack formation, a common limitation of longer wavelength laser. The strong interactions provide for small and smooth excisions, offering depth control on a scale of tens of nanometers. A 157-nm beam homogenization system and a 25x Schwarzschild lens provided a uniform on-target fluence of 9 J/cm2 in a 0.25 mm by 0.25 mm field. Larger work are was enabled by synchronously driving the projection mask and target motion stages. The 0.4 NA lens supported the formation of high- aspect channel walls and surface-relief features as small as approximately 500 nm. Both mask projection and direct writing technique were employed. The novel aspects of the optical beam delivery system are presented together with results on fabricating micro-channels, cutting optical fiber, fabricating surface relief grating and cylindrical lens. The results demonstrate broad application directions for fabricating telecommunication devices, general optical and photonic components, and biological devices.

Fabrication of dielectric optical masks by ablation patterning using a 193 nm laser is demonstrated. Ablation of layer systems that are highly reflective at 193 nm (HR 193nm) is accomplished by using an absorbing layer to initiate ablation. This absorbing layer is deposited on the substrate under the HR system. Thus it is possible to induce spatially defined ablation of the whole stack by irradiating the absorbing layer through the substrate (rear side ablation). Using the system as a mask, i.e. irradiating it from the front side, the reflective layer system prevents penetration of high fluence radiation to the absorbing layer, so that the function of the reflective mask is not restricted. A HR 193 nm system, composed of 42 layers, alternating Al 2 ) 3 and SiO 2 was prepared. The substrate was fused silica. For the absorbing layer (a) HfO 2 and (b) SiO x (x 2 , residual fragments of the absorbing layer diminish the transmission in the ablated areas. In the case of SiO x , which is absorbing at 193 nm for x 2 has high transmission at 193 nm improving the mask performance. For the ablation process single pulse irradiation with a fluence of about 800 mJ/cm 2 is sufficient. The mask has a damage threshold of >1 J/cm 2 .

Based on a recently developed design algorithm a multifaceted diffractive phase element (DPE) has been realized for an excimer laser beam shaping application. The optical reconstruction is presented and the influence of corrections concerning wavefront distortion and coherence is demonstrated.

A high-resolution 157-nm optical system has been developed for the first time to microprocess optical materials with record short-wavelength F2-laser radiation. The F2-laser photons drive strong material interactions in silica glasses for microsculpting surfaces and for imprinting internal refractive index structures. The high-resolution optics deliver a homogenized beam of high on-target fluence (approximately 2.5 J/cm2) for ablation of fused silica and other wide bandgap optical materials. The system resolution is approaching 1-micron lateral and less than 100-nm depth - sub-wavelength features appropriate for defining optical communication components at 1.55-micrometers wavelength. This paper describes this novel processing system and offers prospects for F2-laser microfabrication and trimming of photonic components in the telecommunication and general optics manufacturing fields.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Fresnel-Kinoforms consisting of 121 sub-apertures are used for beam shaping and beam homogenization of partial coherent KrF excimer laser beams. Design and optical reconstruction are presented and discussed.

Ablation of submicron structures on metals and semiconductors is presented using subpicosecond laser pulses at 248 nm. Morphology changes as a function of pulse duration have been investigated. The dynamics of the surface modification has been studied using a pump-probe technique. Diffracted signals of a probe beam on laser induced gratings provide information on the dynamics of the electron phonon interaction, melting and material removal simultaneously. For metals, in the first 5 - 10 ps following irradiation the electron-phonon relaxation dominates the process, followed by melting, expansion and violent material ejection. For semiconductors, rapid amorphization of the surface occurs within a couple of hundred femtoseconds following irradiation, with less pronounced indication for the development of molten material.

Ablation yields and thresholds for 193 nm UV laser ablation of ultrathin HfO2 are presented. The single shot threshold fluence increases approximately linearly with HfO2 thickness form 28 nm to 120 nm. Due to the logarithmic dependence of ablation depth on fluence this result with increasing layer thickness in an exponential increase of fluence necessary for clean ablation of the whole layer. The observed ablation depth for fixed HfO2 thickness can be reproduced phenomenologically by taking ablation from the HfO2 film as well as the quartz substrate into account. As a first approach to a quantitative understanding we calculate numerically the heat evolution in the layered system and identificate ablation with the onset of melting of the absorbing layer. Whereas the ablation curve for a 74 nm thick film can be reproduced that way, this is not the case for the case for the overall thickness dependence of the ablation threshold. This points to possible finite size effects for the phonon-phonon scattering rate in the thin dielectric layers.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A small, fast and low cost device for the measurement of analyte concentrations on nano titer plates is desired. By immuno chemical labelling with dyes these analyte concentrations can be determined by laser induced fluorescence detection. A first highly sensitive instrument for fluorescence excitation and detection has been developed. It is based on a diode laser and a CCD camera. Further reduction in price and size is leading to a second system that uses a micro scanner for the sequential illumination of the NTP. The development of this second instrument is still in progress.

Near UV excimer ablation of transparent polymers can be improved or even enabled by doping using organic dyes. Polymethylmethacrylate (PMMA) and polystyrene (PS) have been investigated using both photostable and photoreactive dopants. The best results with regard to etch quality and effectivity have been achieved with 1,3- diphenyltriazene, which supports the ablation process by photoeliminating nitrogen. Etch rates of 50 jim/pulse can be reached at 308 nm and 351 nra. The etch rate does not depend entirely on the low level absorption coefficient of the doped polymer.