We developed an optofluidic device containing a nanostructured substrate for surface enhanced Raman spectroscopy (SERS). The device is based on a silicon chip, on which structures were fabricated using electron lithography and wet etching to achieve a pattern of inverted pyramids on the surface, which was then covered by gold layer of defined thickness and roughness. The geometry of the surface allows localized plasmon oscillations to give rise to the SERS effect, in which the Raman spectral lines are intensified by the interaction of the plasmonic field with the electrons in the molecular bonds. The SERS substrate was enclosed in a microfluidic system from silicone polymer and glass, which allowed transport and precise mixing of fluids entering the chip, while preventing contamination or abrasion of the highly sensitive substrate. We used this device as a platform for quantitative detection of halogenated hydrocarbons such as 1,2,3-trichloropropane (TCP) in water in submillimolar concentrations. TCP is used in industry and it is a persistent environmental pollutant. The presented sensor allows fast and simple quantification of such molecules and it could contribute to environmental monitoring disciplines as well as enzymologic experiments with genetically engineered dehalogenases, which are potentially useful for bioremediation. This research is supported by Czech Science Foundation (CSF) 16-07965S, infrastructure was supported by MEYS (LO1212, LM2015055) and EC (CZ.1.05/2.1.00/01.0017).
Optofluidics, a research discipline combining optics and microfluidics, currently aspires to revolutionize the analysis of biological and chemical samples, e.g. for medicine, pharmacology, or molecular biology. In order to detect low concentrations of analytes in water, we have developed an optofluidic device containing a nanostructured substrate for surface enhanced Raman spectroscopy (SERS). The geometry of the gold surface allows localized plasmon oscillations to give rise to the SERS effect, in which the Raman spectral lines are intensified by the interaction of the plasmonic field with the electrons in the molecular bonds. The SERS substrate was enclosed in a microfluidic system, which allowed transport and precise mixing of the analyzed fluids, while preventing contamination or abrasion of the highly sensitive substrate. To illustrate its practical use, we employed the device for quantitative detection of persistent environmental pollutant 1,2,3-trichloropropane in water in submillimolar concentrations. The developed sensor allows fast and simple quantification of halogenated compounds and it will contribute towards the environmental monitoring and enzymology experiments with engineered haloalkane dehalogenase enzymes.
The non-reciprocity of magneto-optical reflection response by surface plasmon excitation in the planar Au/Fe/Au/glass nano-systems with prism coupling is studied. These structures are intended as magnetic field sensor units combining magneto-optical (MO) and surface-plasmon-resonance (SPR) effects. The ability of MO-SPR systems to magnetic field sensing is analysed using incidence-angle-depending response function (Rpp(+) – Rpp(-))/(Rpp (+) + Rpp (-)), where Rpp denotes the reflectance of p-polarized beam; and, the sign in upper index relates to the orientation of external magnetic field. The proposed sensitivity criteria F and K (the magnitude and inflexed tangent of the response function oscillation) are applied in transverse MO configuration. Mathematical model based on the own matrix algorithm is applied to simulate the diffraction response to varying external magnetic field at the wavelength 632.8 nm. Obtained theoretical results are compared with experiments realized using the measuring device Multiskop (Optrel GbR, Germany).
The paper is devoted to Au/Fe/Au/glass and Au/Fe/glass structures intended as MO SPR sensor units. The model approach based on matrix algebra is used to describe the response of discussed structures to external magnetic field. The theoretical results are confirmed by experiments realized by Multiscope device. The attention has been focused on a sensitivity of proposed response factors ρ±(Φ) and F to magneto-optical effects. The application of ρ±(Φ) response factor for our structures description is limited. The F factor has practically linear character such as change of external magnetic field and ferromagnetic thin film thickness.
We demonstrate a novel experimental method for improvement of efficiency of structural surface modification of
various solids (PMMA, amorphous carbon) achieved by simultaneous action of XUV (21.6 nm), obtained from high-order
harmonic generation (HHG), and VIS-NIR (410/820 nm) laser pulses. Although the fluence of each individual
pulse was far below the surface ablation threshold, very efficient and specific material modification was observed after
irradiation by a single or a few shots of mixed XUV/VIS-NIR radiation.
We also report results on comprehensive characterization of ultrafast coherent X-ray beamline at Prague Asterix
Laser System (PALS). The beamline is based on 1 kHz, table-top, high-order harmonic generation source capable to
deliver fully coherent beam in the 30 nm spectral range. Ti:sapphire (810 nm, 1 kHz) laser pulses with a duration of 35 fs
and energy 1.2 mJ have been focused into gas cell containing conversion medium (Ar). To achieve highly efficient HHG
we will apply the technique of guided laser pulses. Source parameters were investigated.
We demonstrate a novel experimental method for efficient structural surface modification of various solids (PMMA,
amorphous carbon) achieved by simultaneous action of XUV (21.6 nm), obtained from High-order Harmonic Generation
(HHG), and Vis-NIR (410/820 nm) laser pulses. Although the fluence of each individual pulse was far below the surface
ablation threshold, very efficient and specific material modification was observed after irradiation even by a single shot
of mixed XUV/Vis-NIR radiation.
The desktop capillary-discharge Ne-like Ar laser (CDL) providing 10-μJ nanosecond pulses of coherent 46.9-nm
radiation with a repetition rate up to 12 Hz was developed and built at the Colorado State University in Fort Collins and
then installed in Prague. The beam of the laser was focused by a spherical mirror covered with Si/Sc multilayer coating
onto the surface of poly(methyl methacrylate) - PMMA. Interaction parameters vary by changing the distance between
sample surface and beam focus. The samples were exposed to various numbers of shots. Analysis of damaged PMMA by
atomic force (AFM) and Nomarski (DIC - differential interference contrast) microscopes allows not only to determine
the key characteristics of the focused beam (e.g. Rayleigh's parameter, focal spot diameter, tight focus position, etc.) but
also to investigate mechanisms of the radiation-induced erosion processes.
We present a review of recent development and applications of soft x-ray lasers, undertaken at the PALS Centre. The applications benefit from up to 10-mJ pulses at the wavelength of 21.2 nm. We describe the pumping regimes used to produce this soft x-ray laser, and outline its emission characteristics. A significant fraction of applications carried out using this device includes probing of dense plasmas produced by IR laser pulses and high-energy-density-in-matter experiments. Results obtained in these experiments are reviewed, including x-ray laser probing of dense plasmas, measurements of transmission of focused soft x-ray radiation at intensities of up to 1012 Wcm-2, measurements of IR laser ablation rates of thin foils, and probing high density plasmas by x-ray laser Thomson scattering
The micropatteming of multilayer gratings (MLG) using ultraviolet sub-ps laser pulses is described. A micromachining system operating with a 0.5 ps KrF laser (248 nm) was used. Grating structures with a groove width in sub-pm region were created in Mo/Si, Si/Mo, W/Si and Si/W multilayers (MLs) with 5 (in one case 10) periods, each 7-10 nm thick. Grating area was up to 900 x 900 μm2. Laser fluence on the samples varied between 60 and 710 mJcm-2. Atomic force microscopy, scanning electron microscopy, X-ray reflectivity and X-ray diffraction were used to characterize multilayers and gratings. MIs were locally ablated up to the Si, oxidized Si or glass substrate, or deeper, using from 1 to 5 pulses. The roughness on the surface of lines and in grooves of MLG increased with the depth of ablation. It was caused first of all by debris. The ω-scans around the 1st Bragg maximum show symmetric satellites up to the 2nd or 3rd order, giving the evidence that the ML in MLG is preserved.
An x-ray multilayer mirror, specially designed to produce resonant absorption at a definite angle of incidence, may be used as an angular dispersive element for refractive x-ray radiography. In this method the signal-to-noise ratio can be significantly enhanced due to suppression of the shot noise produced by the direct beam. Refraction contrast of a copper wire 75 microns in diameter and a human hair was observed using Ni/C multilayer mirror with resonant absorption at CuKa radiation. The multilayer structure consisting of 30 bilayers was designed for CuKa radiation so as to have absorbing resonance of the width of about several arc seconds at a grazing angle of 0.8 degrees. A monochromatic probe x-ray beam with a divergence of approximately 5 arc seconds was obtained from a conventional x-ray tube and a double crystal monochromator set in a strongly dispersive configuration. We have developed theoretical basis for this method, and have experimentally proven that it is possible to create critical components for its practical implementation: a multilayer mirror with resonant absorption, an x-ray imaging photon-counting detector with spatial resolution of about several micrometers, and a probe beam with the divergence of several arc seconds. This result proves the feasibility of x-ray refraction radiography using resonantly absorbing multilayer mirrors manufactured by conventional magnetron sputtering technology.
Analysis of refractive index profiles of rugate and quasi- rugate films from measurements requires special techniques to avoid destabilization of solution due to a large number of fitted parameters. Regularization technique suggested recently takes into account a priori information about the index profile by adding the so called stabilizing operator to the merit function. We propose a more general form of this operator and different model of the system thus allowing for better correspondence between the stabilizer and a priori information. The new technique is demonstrated on the analysis of rf magnetron sputtered quasi-rugate films of SiO2/TiO2 with nominally linear material composition profiles and the results are compared to profiles established from Rutherford backscattering spectroscopy measurements.
A series of nitrogenated and nitrogen-free carbon films was prepared under various deposition conditions (substrate temperatures between 40 - 535 degree(s)C and working gas pressures between 0.09 - 5.0 Pa). Rutherford backscattering, Raman scattering, surface profilometry, ellipsometry, hardness and adhesion measurements were performed and results were related to both nitrogen and oxygen content in the layers.
The antireflection coating design on GaAs for the spectral range from 8 micrometers to 12 micrometers is discussed. Based on the comprehensive search technique the best systems of up to 5 layers of ZnS and Ge are presented. To get better antireflection effect the materials with lower refractive indices are needed. Utilization of yttria for this purpose is suggested and optical constants in IR for both evaporated and sputtered layers are established. Though evaporated yttria layers exhibit relatively high absorption in the region of our interest, sputtered films are much better and several systems of up to four layers of Y2O3, ZnS, and Ge are computed by the comprehensive search technique again.
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