Laser Spectroscopic Techniques Research Articles

Pulse heating of water at the surface of gold nanoparticles: Femtosecond laser spectroscopy of energy relaxation of aqueous colloid of plasmonic nanoparticles under strong excitation conditions

The dynamics of differential absorption spectra of gold nanoparticles has been studied by femtosecond laser spectroscopy over a wide range of excitation energy density. The position of the plasmon resonance peak strongly depends on the dielectric properties of the medium, thereby allowing the use of plasmonic nanoparticles as an optical probe. It has been shown that femtosecond laser spectroscopy techniques, involving analysis of differential absorption spectra of gold nanoparticles in aqueous colloid nanolayer, make it possible to characterize the state of a water nanolayer surrounding the nanoparticle. In particular, at a high excitation energy density, the plasmon resonance absorption band exhibits spectral—kinetic features that suggest vaporization in the nanolayer around the gold particle.

Solar cells sensitized with near-infrared absorbing dye: Problems with sunlight conversion efficiency revealed in ultrafast laser spectroscopy studies

Complete solar cells sensitized with cyanine dye MK-245, having near-infrared absorption band optimized for tandem devices, are prepared, characterized and studied by time-resolved laser spectroscopy techniques. The photocurrent of the cell correlates with the amount of residual transient absorption signal, pointing to the poor electron injection as the main factor limiting the sunlight conversion efficiency. The measurements show that the lifetime of the excited state is drastically reduced from about 300 ps in solution to single picoseconds when the dyes are attached to titania nanoparticles. It is due to the self-quenching process that effectively competes with electron injection, even under the presence of co-adsorbent. In addition, high concentration of lithium cations in the electrolyte is necessary to improve electron injection quantum yield. The obtained results should be valid for a large class of similar compounds and reveal the main problems in obtaining sufficient performance of near-infrared absorbing dyes.

Optical Visualization and Spectroscopic Techniques for Probing Water Transport in a Polymer Electrolyte Fuel Cell

AbstractTo solve the critical issues of water management in polymer electrolyte fuel cells (PEFCs), the comprehensive understanding of water transport in the catalyst layer, gas diffusion layer (GDL), electrolyte membrane and gas channel during cell operation is required. In this Minireview, optical visualization and laser spectroscopic techniques for investigating liquid water behavior and water vapor distribution in operating PEFCs are presented. Direct optical observation of water droplet buildup in the GDL and gas channel is conveniently performed using transparent cells. In addition, a novel visualization method using humidity test paper makes it possible to quantitatively measure the water vapor profile along a gas channel. Tunable diode laser absorption spectroscopy is available for noninvasive monitoring of water concentrations in flow channels with a high time resolution. These diagnostic techniques provide information useful for proper water management in PEFCs.

Pressure broadening of Ar and Kr (n+1)s[3/2]2→(n+1)p[5/2]3 transition in the parent gases and in He

Tunable diode laser spectroscopy technique was employed to determine pressure broadening coefficients for the (n+1)s[3/2]2→(n+1)p[5/2]3 transitions in Ar and Kr in RF discharge plasma. The widths of Gaussian and Lorentian components of the absorption lines were determined simultaneously by fitting absorption line profiles obtained in experiments to a Voigt profile. The technique was validated in measurements of pressure broadening coefficient for 811.5nm Ar absorption line in the pressure range of 15–75Torr. The obtained values for these coefficients reduced to 300K are ξAr–Ar=(2.8±0.1)×10−10s−1cm3 for broadening in the parent gas and ξAr-He=(3.2±0.2)×10−10s−1cm3 in helium.For krypton, isotope abundance was accounted for and appropriate fit function was constructed permitting to determine pressure broadening coefficients using the natural mixture of isotopes. For krypton 811.3nm line these coefficients are ξKr-Kr=(2.4±0.2)×10−10s−1cm3 and ξKr-He=(3.1±0.2)×10−10s−1cm3.

Real-time monitoring of changes of the pathogens concentration in water under influence of nanosilver particles by resonance laser spectroscopy techniques

We investigated the nonlinear scattering in solutions of water containing E. coli and the mixture of E. coli and silver nanoparticles. As a result of these investigations, we developed a method of controlling the concentration of pathogenic organisms in the water and the concentration of the nanoparticles influences these organisms. For the study we selected pathogens – goldish staphylococcus, E-coli and coliphage MS-2. Standard biological method is qualitatively in agreement with our results.

Polaron pair mediated triplet generation in polymer/fullerene blends.

Electron spin is a key consideration for the function of organic semiconductors in light-emitting diodes and solar cells, as well as spintronic applications relying on organic magnetoresistance. A mechanism for triplet excited state generation in such systems is by recombination of electron-hole pairs. However, the exact charge recombination mechanism, whether geminate or nongeminate and whether it involves spin-state mixing is not well understood. In this work, the dynamics of free charge separation competing with recombination to polymer triplet states is studied in two closely related polymer-fullerene blends with differing polymer fluorination and photovoltaic performance. Using time-resolved laser spectroscopic techniques and quantum chemical calculations, we show that lower charge separation in the fluorinated system is associated with the formation of bound electron-hole pairs, which undergo spin-state mixing on the nanosecond timescale and subsequent geminate recombination to triplet excitons. We find that these bound electron-hole pairs can be dissociated by electric fields.

Measurement of 7Li/6Li Isotope Ratio Using Phase-Conjugate Degenerate Four-Wave Mixing in a Graphite Furnace

To obtain a Doppler-free resolution, we employ phase-conjugate degenerate four-wave mixing (PCDFWM) to isotope selectively analyze <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li and <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> Li in a graphite furnace atomizer. After the investigation of concentration and power dependences of PCDFWM, the optimal sample concentration and power conjugation are determined. Under the optimized conditions, we measured <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> Li/ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li isotope ratio in Li standard solution with PCDFWM to be 11.571 ± 0.003, which is in good agreement with the value calculated by atomic absorption spectroscopy but has a preferable resolution. The detection limit as 15.54 ng/mL is achieved. The information obtained from this paper suggests that PCDFWM is a reliable laser spectroscopic technique with high resolution in isotope ratio measurement and trace analysis for various applications such as geochemical exploration.

Optical beat-note frequency stabilization between two lasers using a radio frequency interferometer in the gigahertz frequency band

A beat-note frequency stabilization system using a distributed-feedback laser and external cavity laser diode has become a very important technique for laser spectroscopy, where highly stabilized high-frequency beat notes are required. We have developed a simple and versatile system capable of stabilizing the high-frequency beat notes (3 to 11 GHz) of two lasers using a delayed radio frequency self-heterodyne interferometer and have confirmed its basic operation. The frequency stability of the obtained beat notes is higher than 1 MHz in the 3- to 11-GHz frequency range with an average time of 20 s.

Application of R-ICOS laser spectroscopy technique for measurement of absorption in optically dense media

The integral R-ICOS method of three-beam diode laser spectroscopy allows extending the dynamic range of measurements of the absorption coefficient of particles in a medium compared to the conventional ICOS (CEAS) integral absorption technique in an external optical cell. The application of the method for optically dense media is discussed.

Investigation of Interfacial Charge Separation at PbS QDs/(001) TiO2Nanosheets Heterojunction Solar Cell

In the recent years, the heterojunction solar cells based on quantum dots (QDs) have attracted attention due to strong light absorbing characteristics and the size effect on the bandgap tuning. This paper reports on the kinetics of interfacial charge separation of PbS QDs/(001) TiO2 nanosheets heterojunction solar cells. PbS QDs are deposited using a bifunctional linker molecule on two different TiO2 films, i.e., TiO2 nanosheets (with 001 dominant exposed facet) and TiO2 nanoparticles (with 101 dominant exposed facet). Upon bandgap excitation, electrons are transferred from the PbS QDs conduction band to the lower lying conduction band of TiO2. Based on the ultrafast pump-probe laser spectroscopy technique, the kinetics of charge separation is scrutinized at the PbS/TiO2 interface. The interfacial charge separation at PbS/TiO2 nanosheets films made of (001) dominant exposed facets is five times faster than that on (101) dominant exposed facets TiO2 nanoparticles. The quantum yields for charge injection are higher for the (001) TiO2 nanosheets than the (101) TiO2 nanoparticles due to enhanced interfacial interaction with (001) surface compared to the (101) nanoparticles. The superior interfacial charge separation at PbS/(001) nanosheets respect to PbS/(101) nanoparticles is consistent with the higher photocurrent and enhanced power conversion efficiency in the PbS QDs/(001) TiO2 heterojunction solar cell. The use of (001) TiO2 nanosheets can be a better alternative to conventional mesoporous TiO2 films in QD heterojunction solar cells and perovskites-based heterojunction solar cells.

Qualitative elemental analysis of farm animals’ milk adopting laser spectroscopic technique

Information about the elements in milk represents a major tool to identify different milk types and their quality. This is because milk constituents of minerals, proteins and fats differ by different mammals and even for different breeds. In the present work, fresh samples of widely consumed farm animals’ milk, namely from buffaloes, camels, sheep and goats were analyzed qualitatively using laser induced breakdown spectroscopy (LIBS) technique. It was focused on calcium, magnesium, iron, sodium, strontium and barium. Molecular bands of CN in the LIBS spectra were used to study the proteins levels in different milk samples. The results revealed that milk samples from different animals could be characterized as completely different combination of the elements constituents were present in magnesium and iron were higher in goat milk compared to the other animals; in addition, the percentage of barium relative to calcium was lower in all milk samples which confirm plant feeding for all studied animals. In general, this work demonstrates the feasibility of using LIBS as a simple, fast and cost effective technique to perform in situ qualitative analysis of milk samples in dairy farms without any need to transport samples to the laboratories.

Dependence of the catalytic decomposition of PH3 on wire material

The decomposition processes of PH3 on heated W, Mo, Ta, and Ir surfaces were studied using mass spectrometric and laser spectroscopic techniques. For all wire materials, the decomposition efficiency saturated to around 50% at high wire temperatures. The P-atom density also saturated showing only minor dependence on the wire materials. At lower temperatures, however, the production rate of P atoms on Ta was higher than that on W, while that for Mo was lower, suggesting that the decomposition processes are not thermal but catalytic. The production rate on Ir was similar to that on W. Possible decomposition mechanisms are discussed.

A new method for calculation of thick plasma parameters by combination of laser spectroscopy and shadowgraphy techniques

In this paper, a new method is introduced for studying optically thick plasma in local thermodynamic equilibrium condition by laser induced breakdown spectroscopy (LIBS) technique. The method presented here is very simple, exact, and appropriate for simultaneously quantifying the plasma parameters and instrumental function of the experimental system from self-absorbed spectral lines. A LIBS experiment is performed on an aluminum target in air atmosphere by combination of two techniques of shadowgraphy and spectroscopy, and by utilizing a theoretical approach. In this work, plasma parameters can be accurately calculated when the electron density, plasma length and intensities of three spectral lines are experimentally known. This model suggests that instead of using two spectral lines in thin plasmas, three lines are required in thick plasmas for exactly estimating the plasma temperature. In this paper, the temporal evolution of plasma dynamics, such as the number densities of the emitting species, plasma length, velocity of plasma expansion and its temperature variation is obtained by the presented procedure.

A versatile interaction chamber for laser-based spectroscopic applications, with the emphasis on Laser-Induced Breakdown Spectroscopy

The technical note describes the interaction chamber developed particularly for the laser spectroscopy technique applications, such as Laser-Induced Breakdown Spectroscopy (LIBS), Raman Spectroscopy and Laser-Induced Fluorescence. The chamber was designed in order to provide advanced possibilities for the research in mentioned fields and to facilitate routine research procedures. Parameters and the main benefits of the chamber are described, such as the built-in module for automatic 2D chemical mapping and the possibility to set different ambient gas conditions (pressure value and gas type). Together with the chamber description, selected LIBS application examples benefiting from chamber properties are described.

Decay-Assisted Laser Spectroscopy of Neutron-Deficient Francium

This paper reports on the hyperfine-structure and radioactive-decay studies of the neutron-deficient francium isotopes $^{202-206}$Fr performed with the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at the ISOLDE facility, CERN. The high resolution innate to collinear laser spectroscopy is combined with the high efficiency of ion detection to provide a highly-sensitive technique to probe the hyperfine structure of exotic isotopes. The technique of decay-assisted laser spectroscopy is presented, whereby the isomeric ion beam is deflected to a decay spectroscopy station for alpha-decay tagging of the hyperfine components. Here, we present the first hyperfine-structure measurements of the neutron-deficient francium isotopes $^{202-206}$Fr, in addition to the identification of the low-lying states of $^{202,204}$Fr performed at the CRIS experiment.

Comparison of TiO2and ZnO Solar Cells Sensitized with an Indoline Dye: Time-Resolved Laser Spectroscopy Studies of Partial Charge Separation Processes

Time-resolved laser spectroscopy techniques in the time range from femtoseconds to seconds were applied to investigate the charge separation processes in complete dye-sensitized solar cells (DSC) made with iodide/iodine liquid electrolyte and indoline dye D149 interacting with TiO2 or ZnO nanoparticles. The aim of the studies was to explain the differences in the photocurrents of the cells (3-4 times higher for TiO2 than for ZnO ones). Electrochemical impedance spectroscopy and nanosecond flash photolysis studies revealed that the better performance of TiO2 samples is not due to the charge collection and dye regeneration processes. Femtosecond transient absorption results indicated that after first 100 ps the number of photoinduced electrons in the semiconductor is 3 times higher for TiO2 than for ZnO solar cells. Picosecond emission studies showed that the lifetime of the D149 excited state is about 3 times longer for ZnO than for TiO2 samples. Therefore, the results indicate that lower performance of ZnO solar cells is likely due to slower electron injection. The studies show how to correlate the laser spectroscopy methodology with global parameters of the solar cells and should help in better understanding of the behavior of alternative materials for porous electrodes for DSC and related devices.

Measurement of7p1/2-state hyperfine structure and7s1/2-7p1/2transition isotope shift in203Tl and205Tl

A two-step, two-color laser spectroscopy technique has been used to measure the hyperfine splitting of the 7p$_{1/2}$ excited state in $^{203}$Tl and $^{205}$Tl, as well as the isotope shift within the 7s$_{1/2}$ - 7p$_{1/2}$ transition. Our measured values for the hyperfine splittings, 2153.2(7) MHz (in $^{203}$Tl) and 2173.3(8) MHz (in $^{205}$Tl), each differ by 20 MHz from previously published values which quoted comparable precision. The transition isotope shift of $^{203}$Tl relative to $^{205}$Tl was measured to be 534.4(9) MHz. In our experiment, one laser was locked to the thallium ground-state 6p$_{1/2}$ - 7s$_{1/2}$ 378 nm transition, while the second, spatially overlapping laser was scanned across the 7s$_{1/2}$(F=1) - 7p$_{1/2}$(F=0,1) hyperfine transitions. To facilitate accurate frequency calibration, radio-frequency modulation of the laser was used to create sidebands in the absorption spectrum.

Single-Molecule Femtochemistry: Molecular Imaging at the Space-Time Limit

Through a combination of light and electron probes, it may be possible to record single-molecule dynamics with simultaneous sub-Ångstrom spatial and femtosecond temporal resolution. Single-molecule femtochemistry is becoming a realistic prospect through a melding of laser spectroscopy and electron microscopy techniques. The paper by Lee et al. in this issue of ACS Nano takes a significant step toward chemical imaging at the space-time limit of chemical processes. By imaging electroluminescence spectra of single porphyrin molecules with submolecular resolution, the authors extract the implicit femtosecond dynamics of the coupled electron orbital-molecular skeletal motion triggered by a reduction-oxidation scattering process.

An effective method for trapping ion beams in superfluid helium for laser spectroscopy experiments

A novel laser spectroscopy technique -“OROCHI” (Optical Radioisotopes Observation in Condensed Helium as Ion-catcher) has been proposed. This method aimed to investigate the structure of exotic nuclei systematically by measuring nuclear spins and moments. For in-situ laser spectroscopy of atoms in He II, a method to trap atoms precisely at the observation region of laser is highly needed. In this work, a setup composed of a degrader, two plastic scintillators and a photon detection system is further tested and verified for adjusting and checking the stopping position of 84–87 Rb beam. Details of the current setup, experimental results using this method are presented.

Uranium determination in groundwater using laser spectroscopy

AbstractThe aim of this work is to review the laser-based analytical techniques for the quantitative determination of uranium in aqueous solutions. Among the various types of laser-based analytical techniques, two different spectroscopic techniques based on the measurement of laser-induced luminescence of hexavalent uranium ions [U(VI)] in groundwater are reviewed in detail. In the first technique, called time-resolved laser fluorescence spectroscopy, the time-resolved laser-induced luminescence intensities of U(VI) as a function of uranium concentration are measured to obtain the calibration curve. In the second technique, which is based on the simultaneous measurement of the U(VI) luminescence and Raman scattering of water, the calibration curve is obtained by measuring the ratio of the luminescence intensity of U(VI) to the Raman scattering intensity of water for the quantitative determination of uranium. A limit of detection of 0.03 μg/l was achieved at an excitation wavelength of 266 nm using these laser spectroscopic techniques. The results determined using these techniques are in good agreement with the results determined by inductively coupled plasma mass spectrometry (ICPMS). Thus, these laser-based analytical techniques will be useful to personnel requiring a rapid determination of uranium before the shipment of samples to an accredited laboratory, where relatively intricate and expensive apparatuses, such as ICPMS and radiochemical spectrometry, are used.