A heavy water target system for high repetition rate multi-TW lasers as deuteron source will be presented. This self-regenerated ultrathin liquid leaf surface composed from two liquid jets collided from nozzles of 11 um. At the current state of the development, a stable leaf with a length of 1.5 mm is maintained in 10E-4 mbar vacuum. The thickness of the liquid sheet is <200 nm, measured from the modulation of the spectrally resolved interference arising from white light reflection on the front and the back surfaces of the liquid sheet.
Electron beam guns with approximately 10 kW power are used for drying printing colors. As exit window for the
electrons, 15 μm thin Titanium films are used, their thickness is at the current limit for industrial rolling processes.
Thinner exit windows would increase the electron’s transmission and therefore reduce the required acceleration voltage,
power consumption, shielding against X-rays and in the end machine and processing costs. The Titanium films should
locally be thinned to about 5 μm, in the ranges of 3 mm diameter.
Ultra-short laser pulses are well known for high precision micro structuring, as they offer small heat effect zones.
We optimized the processing parameters and the ultra-short laser ablation of thin Titanium foils to achieve high
manufacturing velocity and quality of the surface structure.
Experiments with single pulse laser ablation and different spot diameter were conducted to find a connection between
spot diameter and ablation threshold. The experiments show no dependency of the thresholds on the laser spot diameter..
First Experiments with different parameters were conducted to structure a three dimensional geometry in thin Titanium
foils.
Using planar waveguides as a platform for optical biosensors allows an efficient and selective fluorescence excitation in
close proximity to the waveguide surface. Usually, the fluorescence light that is emitted in the space above the sensor
chip is collected and analyzed by suitable free space optics and a detector. Due to the vicinity of the fluorescent
molecules to the interface of the waveguide layer, a substantial part of the fluorescence light is coupled back into and
collected by the waveguide. The coupling efficiency depends on position, environment and orientation of the molecules.
The utilization of this signal for fluorescence detection and analysis can allow a significant simplification of the optical
instrumentation. We present a fundamental investigation of the fluorescence collection efficiency into the waveguide by
theoretical and experimental means.
We demonstrate the improvement of fluorescence immunoassay (FIA) diagnostics in deploying a newly developed compact diode-pumped solid state (DPSS) laser with emission at 315 nm. The laser is based on the quasi-three-level transition in Nd:YAG at 946 nm. The pulsed operation is either realized by an active Q-switch using an electro-optical device or by introduction of a Cr4+:YAG saturable absorber as passive Q-switch element. By extra-cavity second harmonic generation in different nonlinear crystal media we obtained blue light at 473 nm. Subsequent mixing of the fundamental and the second harmonic in a β-barium-borate crystal provided pulsed emission at 315 nm with up to 20 μJ maximum pulse energy and 17 ns pulse duration. Substitution of a nitrogen laser in a FIA diagnostics system by the DPSS laser succeeded in considerable improvement of the detection limit. Despite significantly lower pulse energies (7 μJ DPSS laser versus 150 μJ nitrogen laser), in preliminary investigations the limit of detection was reduced by a factor of three for a typical FIA.
Experiments in laser physics often require more comprehensive information about a beam than can be extracted from temporal and spatial profile measurement alone. In particular, the wavefront has considerable effect on both irradiance and phase distribution near focus, and thus large impact on the efficiency of non-linear coherent processes such as generation of higher harmonics from femtosecond ultra-short laser pulses. Here we present Hartmann-Shack wavefront measurements of ultra-broadband laser pulses with a spectral bandwidth of >190 THz, which are produced by focusing amplified pulses from a 20 fs Ti:Sapphire oscillator-amplifier system into an Argon filled hollow fibre of 400 μm diameter. After re-compression the pulses were analyzed with the Hartmann-Shack sensor, both at a distance of 140 cm behind the fibre exit and after reflection from a concave mirror (f = 100 mm). Measurements of the overall polychromatic wavefront are faced to a couple of quasi-monochromatic ones covering the whole spectrum. Incoherent superposition of the spectral components yields excellent agreement to the measured overall wavefront, showing that the total wavefront can be sensed reliably by a single measurement. Furthermore, comparison of numerically propagated and measured wavefronts shows good agreement for different spectral components: the measured overall wavefront fits, within sensor accuracy, the numerically propagated one obtained by incoherent superposition of its quasi-monochromatic parts. Drawbacks and opportunities of the Hartmann-Shack technique in ultra-short pulse sensing are briefly discussed.
Resonant reflection filters -- also known as grating waveguide structures -- are characterised by a multilayer configuration including a substrate, waveguide layer and grating(s) at the top of and, in this investigation, also under the waveguide layer. For a specific wavelength at a specific angular and polarisation orientation an incident beam is partly diffracted, guided and rediffracted, leading to vanishing transmission due to destructive interference with the directly transmitted beam, while most of the light is reflected. Since this resonance is a guided mode phenomenon these devices can be used as tunable filters or dichroic elements (reflected wavelength as a function of incident angle) as long as the guided mode condition holds. In this experimental study the behaviour of ultrashort pulses of ~100 fs within structures with various grating depths and, therefore, different spectral resonance bandwidths was investigated under resonance conditions. Spectral and time-resolved measurements in transmission as well as reflection geometry revealed that the ultrashort pulses leaving the structures are time-bandwidth limited, i.e. the spectral bandwidth of the resonant filter determines the pulse length. Group velocity dispersion (GVD) has no important influence since the light is immediately rediffracted after having been coupled into the waveguide layer of the sample.
Beam shaping at the output of optical fibers is required in a variety of applications including optical sensors, telecommunication devices and medical applications. We present a laser micro-machining technique for the fabrication of micro-lenses directly upon the end face of silica fibers using a F2-laser processing station. Ablation is performed in a mask projection arrangement with 25x demagnification. A mask with an occluded circular beam shape is imaged perpendicular to the fiber axis. The fiber is rotated axially while the laser cuts through the fiber, yielding a spherically shaped tip with radius defined by the mask dimensions. Strong 157 nm absorption by the silica glass facilitates precise structuring without micro-crack formation. The quality of the fiber-lenses is characterized by AFM, SEM and by analysing the beam profile at the fiber output.
F2-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 CaF2 beam-homogenization optics and a high-resolution Schwarzschild reflective objective. A square projection mask provided precise excisions in less than 10 x 10 μm2 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.
In this paper, results of the first observation of magnetization-induced second-harmonic generation (SHG) in one-dimensional magneto-photonic microcavities are described. Both significant magnetization-induced rotation of second-harmonic wave polarization and magnetization-induced variations of the SHG intensity are detected at the fundamental wavelengths in the vicinity of microcavity mode.
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.
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.
Linear and nonlinear absorptance in Al2O3 films of different optical thicknesses are investigated using an ArF laser calorimeter. While the linear absorptance at 193 nm shows the linear increase expected for homogenous layers coated with identical process parameters, nonlinear absorptance increases nonlinearly with increasing film thickness. Thus, it cannot be described by a constant nonlinear absorption coefficient. The experimental findings are explained by a simple phenomenological approach using excited states with a finite interaction length longer than the actual film thickness. Due to the observed quadratical increase a new material constant is introduced which describes the nonlinear absorptance behavior correctly.
We introduce a fiber optical sensor system that can be applied to environmental analysis. The compact system is based on laser-induced, time-resolved fluorescence emission spectroscopy. It uses a miniaturised all solid state laser which is operated at 266 nm as the excitation source and a spectrograph/image intensifier/CCD-camera for time-resolved detection of the fluorescence. The versatility of the instrument is demonstrated by the analysis of various substances using multivariate calibration techniques. Xylene could be analysed in natural water samples in the presence of other mono-aromatics with a detection limit of 10 ?g/l. The fluorescence tracer sulforhodamine G was analysed in river water with a detection limit of 10 ng/l. Furthermore the system is able to detect oil contaminations in soil in the concentration range of 100 ppm and above.
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.
We introduce a fiber optical sensor which is capable of analyzing polycyclic aromatic hydrocarbons (PAHs) and monoaromatics like benzene, toluene, xylene, and ethylbenzene (BTXE) in natural water samples. The compact system is based on laser-induced, time-resolved fluorescence emission spectroscopy. It uses a miniaturized all solid state laser which can be operated at 266 nm and 355 nm. The 3-D data set of a time-resolved fluorescence spectrum is reduced to a 2-D data set by a factor based technique, i.e. by dividing the raw data by a decay matrix with exponential decay profiles. The resulting data have a 2-D spectral format but still contain the temporal information. With these data a partial least squares regression has been carried out and optimized for a quantitative evaluation of the data. After the calibration xylene could be selectively analyzed in the 0 - 200 ppb range with a prediction error of 15 ppb. The PAH calibration was able to predict the concentration of 9 out of 15 EPA PAHs with errors between 0.07 (mu) g/l (benzo[a]pyrene) and 1.6 (mu) g/l (anthracene, naphthalene).
The results are presented of pulsed laser diagnostics of the process of pyrolysis of hydrocarbons in a gas, aimed to obtain carbon clusters and to deposit them in a solid phase. The pyrolysis is carried out in a gas flow reactor using homogeneous gas heating by pulsed laser radiation.
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.
We introduce a fiber optical sensors which is capable of analyzing polycyclic aromatic hydrocarbons (PAHs) and monoaromatics like benzene, tolouene, xylene, and ethylbenzene. The compact system is based on laser-induced, time-resolved fluorescence emission spectroscopy. It uses a miniaturized all solid state laser which can be operated alternately at 266 nm and 355 nm. The excitation light is guided through an optical fiber to the sensor head. The fluorescence light is collected by 4 optical fibers, which are placed around the excitation fiber, and guided to a detector, which consists of a spectrograph, a gateable image intensifier and a CCD camera. Time resolved spectra are recorded by moving the gate relative to the laser pulse. The focus of our work is the analysis of water but preliminary results of soil analysis are also presented. Limits of detection have been demonstrated for 15 PAHs from the EPA- list in water and some important mono-aromatics. Additionally some typical applications are presented, i.e. detection of fuel in water and diesel in soil.
In this contribution new physical effects are presented which are observed when different materials are irradiated with high-intensity femtosecond laser pulses. A general classification of regions on the intensity scale is given and experimental results concerning higher-harmonic generation in high-Z materials with laser intensities exceeding 1019 W/cm2 are discussed. Two alternative approaches to the generation of such intensities are described.
The ultrafast relaxation of excitations in a C60 thin film was probed in the energy range 1.6 - 3.4 eV by pump- supercontinuum probe technique with 40 fs time resolution. The relaxation rate shows pronounced spectral dependence with maximum at 2 eV in the region of photoinduced darkening and at 2.4 eV in the region of photoinduced bleaching. It is found that the ultrafast relaxation rate decreases with increasing pumping pulse intensity. The shape of the optical density variation at zero time delay in the region of interband transitions at 2.3 - 3.4 eV is similar to the shape of the second derivative of the stationary absorption spectrum. We propose that this may indicate the creation of a random electric field in the sample during the absorption of the pump pulse. We suggest that the decrease of the relaxation rate with the increase of pumping pulse intensity results from extra-heating of the carriers in hu and t1u bands due to internal conversion from higher excited states, which are populated by two-step photon absorption of the intense pump pulse. Coherent excitation of phonons in the 60 - 300 cm-1 frequency range were detected over a wide spectral probe range. An oscillation with a frequency of 118 cm-1 indicates that the nonequilibrium dimerization of C60 molecules takes place following optical excitation. The full splitting of the Hg(1) intramolecular oscillation mode is observed clearly, which demonstrates that a strong deformation of the molecules upon photon absorption takes place.
The new method of investigation of Fermi surface and Fermi liquid behavior by femtosecond laser spectroscopy is considered. The method consists in study of spectral dependence of the nonequilibrium charge carriers relaxation time by pump-supercontinuum probe technique. Photoinduced optical properties and relaxation of nonequilibrium charge carriers in Au film in a femtosecond time scale are analyzed. It is shown that the relaxation rate sharply slows down in the spectral area related to optical transitions into the vicinity of Fermi level. The form of the peak gives an information on damping of the quasiparpicles near Fermi surface and on deviation of thermalization of nonequilibrium electrons from the conventional equilibrium Fermi-liquid behavior. Studying of ultrafast relaxation time of electron response provides the direct method of investigation thermalization of nonequilibrium electrons in real femtosecond time scale and may give the unique information about deviations from conventional Fermi liquid behavior by femtosecond laser spectroscopy.
Using a planar, linear, waveguide second-harmonic generation was observed by nonlinear evanescent field interaction. In this class of devices phase-matching could be achieved with a periodically structured polymer adsorbate.
We have studied the various nonlinear optical processes that can be described in terms of a third-rank (chi) (2)-tensor or a fourth-rank (chi) (3)-tensor: signals of frequency 2(omega) as in second-harmonic generation due to (chi) (2), and signals of frequency (omega) , 2(omega) , 3(omega) due to (chi) (3). (chi) (3)-type difference-frequency generation is also discussed. Structural information is derived in all frequency domains by analysis of the elements of the respective orientation dependent susceptibility tensor.
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