Intense UV Laser Research Articles

(Invited) Rapid Photo-Charge Mapping of Stainless-Steel Under the Hydrogen Permeation

Photocurrent techniques have been applied to analyze the properties of passive films on metals and their corrosion phenomena. Photocurrent mapping is also used to evaluate the inhomogeneity of, for example, non-uniform corrosion behavior by using a lock-in amplifier to detect a weak photocurrent signal combined with a laser light scanning. This method is, however, takes a long time to acquire a scanning image due to a rather slow time-constant of the lock-in amplifier measurement. In this work, a photo-charge mapping method is developed in which an intense UV laser pulse light (405 nm, 0.5 W in the present study) is focused on the specimen surface and a photo-charge evolved by a single laser pulse is evaluated by integrating the photocurrent using an electronic integrator, as shown in Fig. 1. An intense laser pulse provides a large photocurrent in some condition sufficiently for a single photocurrent pulse analysis. Fast scanning of the laser light is also achieved by using a galvano-scanner. Currently, a time required for one image acquisition is a few minutes which is limited due to the software execution time. In this work, the spatial distribution of hydrogen permeation in a stainless-steel sheet (SUS304, 0.1 mm in thickness) placed in a Devanathan cell was traced under the tensile stress test. Hydrogen was introduced from the backside of the sheet by using the galvanostatic cathodic polarization at –1mA cm–2, and penetrated hydrogen to the front side was oxidized under the anodic polarization at +0.8 V vs. Ag-AgCl R.E. The passive film was pre-formed before the hydrogen penetration. Absorption of hydrogen into stainless steel caused a drastic increase of photocurrent on the n-type semiconductor passive film due to the photo-assisted oxidation of permeated hydrogen atom via a stainless-steel sheet, i.e., hydrogen atoms can be effectively oxidized by the holes generated by UV irradiation in the passive film. In the photo-charge image shown in Fig. 1, left half of the observed area (4mm x 4 mm, 40 x 40 pixel) was penetrated by hydrogen from the backside where the increase of photo-charge was observed. The Devanathan cell was combined with a tensile tester, and a photo-charge map was traced during the hydrogen loading under the loading condition until the notched sample was cleaved. The photo-charge intensity increased around the notch before cleavage, probably due to an increase of hydrogen concentration penetrated or thickening of the passive film. Figure 1

FBG Sensors for Environmental and Biochemical Applications—A Review

Sensors play a large role in monitoring and ensuring that environmental parameters satisfy industrial requirements. They offer crucial safety measures in the early detection of hazards. Conventional electrical sensors possess several drawbacks that hinder their use in environmental sensing. Research has explored and optimized optical-based sensors because they are more robust, immune to electromagnetic interference and offer multiplexing capabilities for sensor arrays accompanied by ease of modification to cater to different measurands. Fibre Bragg grating is the perturbation of the refractive index imprinted within the core of an optic fibre via an intense UV laser. The gratings, when perturbed by external parameter changes, will induce a shift in their wavelength, indicating detection. With modifications such as hygroscopic coating and different grating profile imprinting, FBG can detect various physical and chemical parameters. Environmental, pharmaceutical and biochemical fields can benefit from FBG sensing because their parameters affect not only their product quality but also the lives of consumers. This review discusses some of the FBG sensors that have been proposed to serve in environmental and biochemical applications.

Response of nonequilibrium nonstationary plasma created by intense femtosecond UV laser pulse in rare gases: emission in the THz frequency band

SynopsisWe analyse the response of the current in plasma created in the process of gas ionization by an intense UV laser pulse in the terahertz frequency band. Our consideration allows us to take into account both temporal retardation of the EVDF evolution with respect to the external electric field and the effect of the relaxation of the strongly nonequilibrium EVDF due to elastic electron - atomic collisions The suggested theory enables to properly describe propagation of short and ultra-short THz pulses in laser plasma waveguides.

The response of nonequilibrium nonstationary plasma created by an intense femtosecond UV laser pulse in rare gases to the emission of the THz frequency band

We suggest a new approach for the analysis of the response of plasma created in the process of multiphoton gas ionization by means of an intense UV laser pulse to the terahertz radiation. It is based on the kinetic Boltzmann equation for the temporal behavior of the electron velocity distribution function (EVDF) in an arbitrary nonmonochromatic external electric field and allows us to take into account both the temporal retardation of the EVDF evolution with respect to the external electric field and the effect of relaxation of the strong nonequilibrium electron energy spectrum due to elastic electron—atomic collisions during the external field action. The suggested consideration provides the basis for the theoretical analysis of short and ultra-short (up to one or two periods of oscillations) THz pulse transportation in plasma waveguides formed by high-intensity laser pulses.

Amplified spontaneous emission from a surface-modified GaN film fabricated under pulsed intense UV laser irradiation

We propose a simple method for fabricating random structures directly on Mg-doped GaN thin films. The process is relatively simple, involving only irradiation with strong UV pulses from a fabrication laser on the thin-film surface. After intense UV laser pulses (>400 MW/cm2) are irradiated on the flat GaN film, the surface is roughened and quasi-periodic structures form. When the roughened surface is excited with laser light of intensity about 10 times smaller than the fabrication laser intensity, emission increases around 367 nm, and spectral narrowing and threshold behavior are observed. Because such behaviors are not observed without the application of intense laser irradiation, we conclude that amplified spontaneous emission is induced in the modified GaN surface by the intense UV laser pulse irradiation. This method offers the possibility of easy and direct fabrication of microscale random-laser devices on semiconductor substrates.

The influence of co-doping agents on bismuth clustering in silica synthesized by SPCVD

We investigated the variation of near-infrared (NIR) luminescence spectra of bismuth-doped silica-based glasses caused by exposure to intense deep UV (193 nm wavelength) laser radiation. Bismuth-doped optical waveguides consisting of silica with additives of Al and P as the light-guiding core, synthesized via surface-plasma chemical vapour deposition (SPCVD) technology, served as the samples in our experiments. Spectra of steady-state NIR luminescence excited by 808, 904, and 970 nm wavelength laser diodes were measured in a wavelength band of 1-2 μm at temperatures of 105 and 300 K. We found that exposing the glass to intense ArF excimer laser radiation leads to NIR luminescence integral intensity and spectrum profile changes. The observed changes are discussed in the assumption that the UV laser exposure causes photoinduced rearrangement of the glass network in the vicinity of bismuth inclusions. It is expected that the latter are present in the glass network in the nature of separate ions, atoms, as well as 3D clusters.

Ultraviolet light-induced terahertz modulation of an indium oxide film.

Active ultraviolet light-induced terahertz modulation of an indium oxide film is investigated. A large absorption modulation of ~66% is achieved upon illumination with a low intensity UV laser (11 mW/cm2). The interaction between indium oxide and a flexible metamaterial structure is investigated owing to the large UV-induced enhancement of photo carriers observed in an indium oxide film. We are able to realize absorption peak shifts of 37 GHz by changing the UV excitation light intensity. We also propose a multi-frequency switch by building a circular metallic split ring resonator whose gaps are filled with silicon, germanium, and indium oxide. In future, a photo-excited tunable multi-frequency metamaterial switch can be realized by irradiating the structure with multi-wavelength laser beam.

Control of Charge Transfer in C60–ZnO Composite Under the Influence of UV Laser Radiation by the Methods of Raman Spectroscopy and Photoluminescence

Raman and photoluminescence spectra of nanostructured ZnO films with adsorbed C60 molecules were studied. The possibility of intensive C60–ZnO electronic coupling forming in this composite was investigated. It is shown that such an electron coupling can be significantly enhanced by irradiating the composite with high intensity UV laser radiation (λ = 325 nm).

Circular dichroism measurements at an x-ray free-electron laser with polarization control.

A non-destructive diagnostic method for the characterization of circularly polarized, ultraintense, short wavelength free-electron laser (FEL) light is presented. The recently installed Delta undulator at the LCLS (Linac Coherent Light Source) at SLAC National Accelerator Laboratory (USA) was used as showcase for this diagnostic scheme. By applying a combined two-color, multi-photon experiment with polarization control, the degree of circular polarization of the Delta undulator has been determined. Towards this goal, an oriented electronic state in the continuum was created by non-resonant ionization of the O2 1s core shell with circularly polarized FEL pulses at hν ≃ 700 eV. An also circularly polarized, highly intense UV laser pulse with hν ≃ 3.1 eV was temporally and spatially overlapped, causing the photoelectrons to redistribute into so-called sidebands that are energetically separated by the photon energy of the UV laser. By determining the circular dichroism of these redistributed electrons using angle resolving electron spectroscopy and modeling the results with the strong-field approximation, this scheme allows to unambiguously determine the absolute degree of circular polarization of any pulsed, ultraintense XUV or X-ray laser source.

Laser-induced incandescence applied to dusty plasmas

This paper reports on the laser heating of nanoparticles (diameters μm) confined in a reactive plasma by short (150 ps) and intense ( mJ) UV (355 nm) laser pulses (laser-induced incandescence, LII). Important parameters such as the particle temperature and radius follow from analysis of the emission spectrum of the heated nanoparticles. The nanoparticles are not ideal black bodies, which is taken into account by calculating their emissivity using a light-scattering theory relevant to our conditions (Mie theory). Three sets of refractive index data from the literature serve as model input.The obtained radii range between 100 and 165 nm, depending on the choice of refractive index data set. By fitting the temperature decay of the particles to a heat exchange model, the product of their mass density and specific heat is determined as J K−1 cm−3, which is considerably smaller than the value for bulk graphite at the temperature our particles attain (3000 K): 4.8 J K−1 cm−3.The particle sizes obtained in situ with LII are compared with ex situ scanning electron microscopy analysis of collected particles. Quantitative assessment of the LII measurements is hampered by transport of particles in the plasma volume and the fact that LII probes locally, whereas the samples with collected particles have a more global character.

Photoluminescence of Cr-doped TiO2 induced by intense UV laser excitation

Nanocrystalline anatase (A) and rutile (R) TiO2 were synthesized by the thermal hydrolysis and then were surface doped with Cr ions by adsorption. The samples were characterized by X-ray diffraction, X-ray fluorescence, Raman spectroscopy, optical absorption and photoluminescence (PL) methods. It is found that the PL emission and optical absorption near the band gap edge occur with the same electronic transitions in TiO2. The Cr3+ doping leads to the blue and red shifts of the PL peaks in A/Cr TiO2 due to the Burstein–Moss and band tailing effects, respectively. The Auger type non-radiative recombination in R/Cr TiO2 quenches the PL emission intensity. For anatase samples at low concentrations of Cr ions (0.5at%) the PL emission increases compared to the undoped A TiO2 due to the formation of additional radiative recombination centers. At higher contents of Cr (1.0at%), the PL intensity decreases due to the concentration quenching effect.

Spectroscopy of atom and nucleus in a strong laser field: Stark effect and multiphoton resonances

The consistent relativistic energy approach to atoms in a strong realistic laser field, based on the Gell-Mann and Low S-matrix formalism, is applied in the study of resonant multiphoton ionization of krypton by intense uv laser radiation and for the computation of the resonance shift and width in krypton. The approach to the treatment of the multiphoton resonances in nuclei is outlined for the 57Fe nucleus.

Measurement of the drift field in the ARGONTUBE LAr TPC with 266 nm pulsed laser beams

ARGONTUBE is a liquid argon time projection chamber (LAr TPC) with a drift field generated in-situ by a Greinacher voltage multiplier circuit. We present results on the measurement of the drift-field distribution inside ARGONTUBE using straight ionization tracks generated by an intense UV laser beam. Our analysis is based on a simplified model of the charging of a multi-stage Greinacher circuit to describe the voltages on the field cage rings.

SFRR-E Basic Science Lecture (Elsevier sponsored) - Oxidative degradation pathways of cellular DNA: product formation and mechanistic insights

More than 100 oxidized purine and pyrimidine nucleosides including hydroperoxides and diastereomers have been characterized so far in extensive model studies. However, much less information is currently available on the oxidatively generated base damage to cellular DNA at the exception however of the overwhelming modifications produced by singlet oxygen ((1)O2). This is mostly due to analytical difficulties that are now, at least, partly overcome with the advent of the accurate and sensitive high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS). Hydroxyl radical ((•)OH) and one-electron oxidants that may be either endogenously formed through oxidative metabolism, phagocytosis, inflammation and other pathological conditions are predominantly at the origin of oxidatively generated damage to cellular DNA. It is worth mentioning that exposure of cells to exogenous physical agents (UVA light, high intensity UV laser, ionizing radiation) and chemicals such as bromate may also induce oxidatively generated damage to DNA. Emphasis is placed in this presentation on the critical survey of the main recently available information concerning the formation of (1)O2, (•)OH and one-electron oxidant-mediated single and more complex DNA damage (tandem lesions, intra- and interstrand cross-links, DNA-protein cross-links) arising from one radical hit. Evidence was provided that (•)OH and one-electron oxidants, through the generation of neutral radicals and radical cations respectively from nucleobases, are able to induce partly common degradation pathways. In addition selective oxidative reactions giving rise to specific degradation products of (•)OH and one-electron oxidation reactions that can be used as representative biomarkers of these oxidants have been identified. Emphasis was recently placed on the detection of oxidatively generated damage to cytosine and 5-methylcytosine in human cells.

Oxidatively generated base damage to cellular DNA by hydroxyl radical and one-electron oxidants: Similarities and differences

Hydroxyl radical (OH) and one-electron oxidants that may be endogenously formed through oxidative metabolism, phagocytosis, inflammation and pathological conditions constitute the main sources of oxidatively generated damage to cellular DNA. It is worth mentioning that exposure of cells to exogenous physical agents (UV light, high intensity UV laser, ionizing radiation) and chemicals may also induce oxidatively generated damage to DNA. Emphasis is placed in this short review article on the mechanistic aspects of OH and one-electron oxidant-mediated formation of single and more complex damage (tandem lesions, intra- and interstrand cross-links, DNA–protein cross-links) in cellular DNA arising from one radical hit. This concerns DNA modifications that have been accurately measured using suitable analytical methods such as high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. Evidence is provided that OH and one-electron oxidants after generating neutral radicals and base radical cations respectively may partly induce common degradation pathways. In addition, selective oxidative reactions giving rise to specific degradation products of OH and one-electron oxidation reactions that can be used as representative biomarkers of these oxidants have been identified.

Laser-Excited Excitonic Luminescence of Nanocrystalline TiO2 Powder

Titanium dioxide (TiO2) nanocrystalline powders were prepared by the thermal hydrolysis method in the form of pure anatase or rutile and were investigated by X-ray diffraction, X-ray fluorescence, FT-Raman spectroscopy, optical absorption, and photoluminescence (PL) methods. PL spectra were studied under the intense UV laser excitation at 337.1 nm (3.68 eV) at room temperature. Some interesting features in the PL spectra including the well-resolved peaks of excitonic and band-band transitions in TiO2 were observed for the first time. It is shown that PL bands with peaks at 2.71–2.81 eV and its phonon replicas in anatase and rutile TiO2 arise from the excitonic e− − ℎ+ recombination via oxygen vacancies. The excitonic peak at 2.91 eV is attributed to the recombination of self-trapped excitons in anatase or free excitons in rutile TiO2. The PL peaks within 3.0–3.3 eV in anatase TiO2 are ascribed to indirect allowed transitions due to the band-band e− − ℎ+ recombination. The peaks at 3.03 and 3.26 eV are attributed to the free exciton emission near the fundamental band edge of rutile and anatase TiO2, respectively.

Single-component plasma of photoelectrons

Ten-nanosecond pulses of photoelectrons liberated by intense UV laser pulses from a thin gold layer are captured into a single-component plasma that is ideally suited to cool antiprotons (p¯) for antihydrogen (H¯) production. Up to a billion electrons are accumulated using a series of laser pulses, more than are needed for efficient p¯ cooling in the large traps now being used for loading p¯ for H¯ production. The method is demonstrated within an enclosed vacuum space that is entirely at 4 K, and is thus compatible with the exceptional cryogenic vacuum that is desirable for the long-term storage of antihydrogen. The pitfalls of other electron accumulation methods are entirely avoided, including the particle heating and declining efficiency of field emission point loading, and the heat load and contamination of thermionic emission methods.

Laser Irradiation of Polymer-Doped Cryogenic Matrices

Interactions between intense (1019 photons/cm 2 per shot) UV laser light and doped ice matrices were studied by the Matrix-Assisted Pulsed Laser Evaporation (MAPLE) deposition technique. Water, isopropanol, acetone and toluene ice matrices have been used as hosts for the biotechnologically important polymer – polyethylene glycol (PEG). The polymer–matrix system was irradiated under vacuum conditions with high-intensity laser beam at 355 nm in the fluence range 2–10 J/cm 2 . We have explored the ejection of material from the ices in terms of light absorption by the matrix and photochemical interactions between matrix and polymer molecules during the irradiation process. The transfer of polymer from the matrix to a substrate has been studied on the basis of deposition rates measured with a quartz crystal microbalance (QCM) and Fourier-Transform Infrared (FTIR) spectra recorded from the deposits.

Cluster formation at metal surfaces under bombardment with SFm+ (m=1,…,5) and Ar+ projectiles

We investigate the formation of ionic and neutral clusters emitted from a polycrystalline indium surface under bombardment with SF m + ( m = 1, …, 5) and Ar + projectile ions at 10 keV impact energy. Mass spectra of secondary ions and sputtered neutral particles are recorded under otherwise identical conditions. The neutral species are post-ionized prior to mass analysis by means of single photon-ionization using an intense UV laser at a wavelength of 193 nm. It is found that the measured secondary ion signals increase much more than those of the corresponding neutral particles if SF m + projectiles are used instead of Ar + ions, indicating that the ionization probability under bombardment with SF m + is enhanced by a chemical matrix effect induced by fluorine incorporation into the surface. Interestingly, the largest values of the ionization probability are observed for SF 3 + projectiles. The total sputtering yield is found to be larger for SF m + compared to Ar + projectiles and to increase linearly with increasing m . Both findings are shown to be understandable in the framework of linear cascade sputtering theory. The partial sputtering yields of In n clusters exhibit a stronger enhancement than the sputtered monomers, the magnitude of the effect increasing with increasing cluster size and projectile nuclearity.

Cluster formation at metal surfaces under bombardment with [formula omitted] (m = 1, …, 5) and Ar+ projectiles

We investigate the formation of ionic and neutral clusters emitted from a polycrystalline indium surface under bombardment with SFm+ (m=1,…,5) and Ar+ projectile ions at 10 keV impact energy. Mass spectra of secondary ions and sputtered neutral particles are recorded under otherwise identical conditions. The neutral species are post-ionized prior to mass analysis by means of single photon-ionization using an intense UV laser at a wavelength of 193 nm. It is found that the measured secondary ion signals increase much more than those of the corresponding neutral particles if SFm+ projectiles are used instead of Ar+ ions, indicating that the ionization probability under bombardment with SFm+ is enhanced by a chemical matrix effect induced by fluorine incorporation into the surface. Interestingly, the largest values of the ionization probability are observed for SF3+ projectiles. The total sputtering yield is found to be larger for SFm+ compared to Ar+ projectiles and to increase linearly with increasing m. Both findings are shown to be understandable in the framework of linear cascade sputtering theory. The partial sputtering yields of Inn clusters exhibit a stronger enhancement than the sputtered monomers, the magnitude of the effect increasing with increasing cluster size and projectile nuclearity.