Florent Réal and Valérie Vallet
Univ. Lille, CNRS, UMR 8523 - PhLAM - Physique des Lasers Atomes et Molécules, F-59000 Lille, France
The luminescence properties of the [UO 2 Cl 4 ] 2 – complex in an organic phase, especially the influ-
ence of large organic counter cations, have been studied by time-resolvedlaser-inducedfluorescencespectroscopy (TRLFS) and ab initio modeling. The experimental spectrum was assigned by vi- bronic Franck-Condon calculations on quantum chemical methods on the basis of a combination of relativistic density functional approaches. The shape of the luminescence spectrum of the uranyl tetrachloride complex is determined by symmetrical vibrations and geometrical change upon emis- sion. The possible change in the luminescence properties depending on the first and second uranyl coordination spheres was predicted theoretically for the [UO 2 Br 4 ] 2 – and [R 4 N] 2 [UO 2 Cl 4 ] ([R 4 N] =
solution – 99:1 (v:v) n-dodecane:1-decanol – containing Aliquat ® 336 at 10 −2 M in a thermomixer apparatus under
the following conditions: T = (293 ± 1) K; 1400 rpm; agita- tion time = 48 h. After centrifugation, the concentration of U remaining in the aqueous phase was determined by inductively coupled plasma mass spectrometry (ICP-MS) using a quadrupole ICP-MS spectrometer 7700x (Agilent Technologies). Duplicate experiments showed that the reproducibility of these measurements was within 10 %. After separation, the solutions were analysed in TRLS in 1 cm fluorescence cuvette (Hellma QS-111-10-40).
Femtosecond time-resolved methods involve a pump-probe configuration in which an ultrafast pump pulse initiates a reaction or, more generally, creates a nonstationary state or wave packet, the evolution of which is monitored as a function of time by means of a suitable probe pulse. Time-resolved or wave packet methods offer a view complementary to the usual spectroscopic approach and often yield a physically intuitive picture. Wave packets can behave as zeroth-order or even classical-like states and are therefore very helpful in discerning underlying dy- namics. The information obtained from these experi- ments is very much dependent on the nature of the final state chosen in a given probe scheme. Transient absorption and nonlinear wave mixing are often the methods of choice in condensed-phase experiments because of their generality. In studies of molecules and clusters in the gas phase, the most popular methods, laser-inducedfluorescence and resonant multiphoton ionization, usually require the probe laser to be resonant with an electronic transition in the species being monitored. However, as a chemical reaction initiated by the pump pulse evolves toward products, one expects that both the electronic and vibrational structures of the species under observa- tion will change. Hence, these probe methods can be * To whom corresondence should be addressed. A.S.: telephone
In this work, the interactions of salicylic acid, humic acid and fulvic acid with Eu 3+ were studied by steady-state and time–resolvedlaser–inducedfluorescence
spectroscopy focusing on the ligand fluorescence emission using a nanosecond pulsed laser. Lifetime analysis using Stern–Volmer plot showed that part of dy- namic quenching process or both static and dynamic quenching contributed to the global quenching of fluorescence in the case of salicylic acid-Eu 3+ interaction.
3.3 LS-SVM model
The LS-SVM model was derived using a theoretical calibration set obtained using the diffusion equation, applied for ρ = 6mm and a time resolution of 2.93ps. Each signal was divided by its maximum in order to get rid of irradi- ating signal intensity level. For improving the model efficiency, the temporal window t = 43ps to 900ps was selected where curves were significantlly dif- ferent. The curve start untill t = 43ps was discard because there were no significant differences between curves. The temporal window ranging from t = 43ps till 900ps was chosen for our modelisation. To span the absorp- tion and scattering variations of apple 20 , a mixture design was set up as
The distribution of kinetic energy per deuteron is shown in Fig. 1 for linearly polarized 8.6 and 40 fs pulses.
In both cases, the peak intensity is 5 10 14 W=cm 2
. The vertical axis is normalized at 3 eV. For the 40 fs pulse, the energy spectrum is dominated by a peak around 3 eV with a smaller peak observed at 0:7 eV. Those features are the signature of laser field induced processes — bond soft- ening and enhanced ionization— discussed below.
Isolated Nanoparticle Analysis by Laser-Induced Breakdown Spectroscopy Submitted to symposium X : New frontiers in laser interaction: from hard coatings to smart materials
We propose a method for analyzing the elemental composition of isolated nanoparticles. It is based on Laser-Induced Breakdown Spectroscopy (LIBS). LIBS allows remote specific detection of most of the chemical elements in a sample and at very low concentrations. We propose a new experimental setup in which we perform the laser-particle interaction in vacuum, on a single nanoobject. A small part of the aerosol stream is sampled and driven to an aerodynamic lens system. The latter produces a dense and collimated beam of nanoparticles under vacuum from the atmospheric pressure aerosol flow. The photon signal from the plasma is collected by an UV-compatible optical fiber connected to a spectrograph. As the interaction takes place at low pressure, the photons are emitted only from particles. Unlike previous experiments, the background from interaction with the gaseous
In conclusion, we have shown that time-resolved high- harmonic spectroscopy is a powerful method for probing the electronic dynamics associated with nonadiabatic dynamics in molecules. The sensitivity of the method to variation of the vertical ionization potentials will be most relevant when the wave packet remains localized along the coordinate(s) that strongly modulate(s) the I p , like in diatomic molecules [ 5 , 6 ] or in polyatomic molecules with a single soft coor- dinate [ 3 ]. On longer time scales, and more generally in larger polyatomic molecules, the sensitivity of the method to electronic population dynamics is expected to dominate. This sensitivity may become a powerful asset in studying electronic dynamics in photochemical switches or during pericyclic reactions. We note that in the case of NO 2 , the sensitivity to the population dynamics comes almost exclusively from the time- and coordinate-averaged difference in I p between the AT and XS channels. This is the case because the two channels correspond to ionization from the same orbital. However, the ground and excited states will in general ionize from different orbitals, in which case the method will be sensitive to differences in the phase and amplitude of recombination matrix elements, as well as the ionization rates, giving direct access to the evolving electronic structure of the transient molecule.
Figure 1 shows a schematic diagram of the experimental setup and a picture of how the probe is set up in our laboratory. The bottom end of a tube evacuated with an inert gas (argon or nitrogen) is inserted inside the melt. The gas flows continuously thus creating bubbles at the end of the tube. A laser pulse creates plasma on the internal surface of the bubble. The light emitted by the plasma is collected and sent to a remote spectrometer via an optical fiber. The remote spectrometer and camera are used to record the emission spectrum which is then analyzed using a computer (not shown).
et al. tried to adjust the focusing distance to adapt the large variation of sample heights measured by a laser triangulation sensor. And to further reduce the height variation, a tilted conveyor which kept the samples sliding against the edge was proposed as shown in figure 1 . While facing a much larger variation on a conveyor belt, it is arduous to compensate the variation dynamically. In this sense, part of tolerance for the variation depending on observation depth could be taken into consideration when designing an optical system. According to the laser properties, observation depth can be calculated through the Rayleigh distance .
National Research Council Canada (NRC), Industrial Materials Institute (IMI), Boucherville (QC), J4B 6Y4, Canada
Laser-Induced Breakdown Spectroscopy (LIBS) is a method of optical emission spectroscopy that uses laser-generated plasma as the source of vaporization, atomization and excitation. LIBS is being used as an analytical method by a growing number of research groups. Although the LIBS method has been in existence for more than 40 years, prior to 1980, interest in the technology centered mainly on the basics of plasma formation. A few instruments based on LIBS have been developed but have not found widespread use. In the last decade, there has been a renewed interest in the method for a wide range of applications. This is due to the unveiling of significant technological developments in the components (lasers, spectrometers, detectors) used in LIBS instruments as well as emerging needs to perform real time measurements under conditions to which conventional techniques cannot be applied.
Keywords—FPGA, Real-time, Time correlated Single Photon Counting, SPAD, Microfluidic, Droplet sorting, Screening,
I. I NTRODUCTION
High-Throughput Screening of biomolecule in the field of pharmacology and biochemistry is a technic used to identify within a chemical library the molecules that have new properties or are biologically active. A microfluidic circuit coupled with fluorescence detection is an excellent tool for the application of High Throughput Screening (HTS)  and Fluorescence Activated Cell Sorting (FACS) . Indeed, the fluorescence Quantum Yield (QY) of fluorescently labeled molecules can be significantly reduced upon interaction with other molecules. In Förster Resonance Energy Transfer (FRET)-based assays, the fluorescence yield of the excited “donor” molecule is quenched if its excitation energy is efficiently transferred to a FRET “acceptor” in close proximity. As a consequence, the measure of the fluorescence QY is the indication of the biomolecular interaction. Generally, the fluorescence QY is detected by measuring the fluorescence intensity, but this last can be affected by other parameters such as fluorophore concentration or excitation light intensity. On the contrary, Fluorescence Lifetime (FLT) detection is potentially much more accurate to assay biomolecular interactions because the latter is an intrinsic determination of the fluorescence QY independent of the other parameters. This is the reason why Fluorescence Lifetime Imaging Microscopy (FLIM) has been intensively developed for the analysis of cell biology . For the same reason, FLT detection is expected to enhance the reliability of biomolecular interaction assays 6]. The current commercial plate readers for HTS are able to read plate up to 1536 microwells plate within a few minutes in the FLT mode , whereas a rate of a few thousands of droplets per second can be achieved with a microfluidic channel. Thus, the use of
system to characterize a DL on JET divertor by LIBS analytical method. For our LIBS measurements in JET, it was necessary to satisfy rigid limi- tations imposed by the JET authorities. They were as follows: a limited 5-day period was allowed for LIBS experiments (including installation, adjustment, and measurements); LIBS optical scheme insertion should not upset the operation of the EDGE LIDAR diagnostics scheme; the tar- get (the zone under analysis) was in vacuum chamber at 5 m distance from the vacuum chamber optical window and without an access for operator. In addition to these limitations and dif ﬁculties, we should also mention that in the available EDGE LIDAR system, the laser beam is focalized not on the divertor tiles, but rather on the fusion plasma. This particular feature of the system results in the limited intensity on the target (divertor tile) which was not enough for LIBS analyses. In our previous experiments in JET, it was revealed that a large laser spot (15 –20 mm diameter) does not create any detectable LIBS signal. To Fig. 2. The examples of LIBS spectra obtained from DL on the JET divertor tile with the laser pulse energy (E = 3.2 ± 0.5 J) and with the optimal set of registration parameters: 200 μm spectrometer slit width, 180 ns ICCD camera delay, 10 μs gate width, vacuum. (a) E = 3.0 J, MCP gain = 25, after 1st laser shot, (b) E = 3.3 J, MCP gain = 100, after 5th laser shot, (c) E = 3.0 J, MCP gain = 100, after 1st laser shot.
The results obtained when varying each parameter separately (laser energy, focus, distance and pressure) are summarized in Table 2 as point to point standard deviation. As an overall outcome, the tested normalizations generally reduce variations of the hydrogen signal. Table 2 shows that normalization to total spectrum, VNIR spectrum, neutral carbon at 248 nm, and oxygen lines, seem to produce more ro bust results than normalization to continuum or carbon at 658 nm. While the table summarizes data as standard deviation, we discuss here the variations with the parameters through minimum to maxi mum or signal increase vs. decrease. Using the ﬁrst shots on dust and varying the distance from 2.2 to 4 m, the hydrogen signal decreases by 75% but only changes within 2.2%, 8% and 11% when normalized to ox ygen, neutral carbon at 248 nm, and continuum, respectively (Fig. 3). The effect of laser energy is also reduced by the different normalizations. Whereas the hydrogen signal decreases by 30% when the energy chang es from ~14 mJ to ~10 mJ, it only changes within 1% and 4% of the aver age when normalized to neutral carbon and oxygen, respectively. However, normalization by the carbon ion peak at 658 nm does not pro duce the same result. Indeed, with the energy change from ~ 14 mJ to ~ 10 mJ, the intensity of this peak decreases by ~ 46%, while hydrogen only decreases by 30%, therefore the signal normalized to this peak in creases for decreasing laser energy. The hydrogen signal normalized to carbon at 658 nm also increases with distance (Fig. 3D). This suggests that the carbon peak at 658 nm is biased differently with laser irradiance than the other proxies. This behavior may be explained by the ionic na ture of the doublet emission peak, whereas the carbon at ~248 nm and oxygen triplet at ~ 778 nm are neutral atomic emission peaks. The re sults in varying the laser focus show that the signal decreases by ~50% between best focus and out of focus limits. Normalization reduces these variations, signi ﬁcantly suppressing correlation with focus posi tion (Fig. 5).
Due to the fact that immediately after pulsed excitation at 500 nm we observe absorption at both 5460 and 6130 nm, the geometry of ES is very likely a kinked NO conﬁguration which is agreement with DFT calculations that propose an Fe N O angle in the range of 40 50° as proposed by DFT calculations [16 18] . The minimum of the energetic position of ES is unknown, but we know that the crossing of GS and MS2 is at 1.43 eV  and so 1.06 eV below the excitation with 2.49 eV. Then a relaxation from ES into GS and MS2 by occupation of highly excited NO vibrational levels that are energetically close to the NO vibrational levels of ES can occur within s = 300 fs. A precedent relaxation within ES would need more time and we therefore exclude this possibility. This fast decoupling of the ES towards MS2 or back to GS is in accordance with the results of the timeresolved study in the visi ble range  where an occupation of MS2 within 300 fs was found. Thus the rotation of the NO ligand both towards 90° as well a back to 0° occurs with s = 300 fs. We can now specify that after this ﬁrst fast relaxation the molecules are in a highly vibrationally excited state of the corresponding ground states (GS or MS2).
The laser-induced breakdown spectroscopy (LIBS) technique is based on the spectroscopic analysis of light emission from the plasma generated by focusing a powerful laser beam on a target. LIBS is being used as an analytical method by a growing number of research groups. The growing interest in LIBS, particularly in the last decade, has led to an increasing number of publications on its applications, both in the laboratory and in industry. Recent developments in technology and research in spectroscopic detectors have suggested a promising future and an improvement of measurements in plasma spectroscopy. Undoubtedly, the advent of high quality solid-state detectors is revolutionizing the field of atomic spectroscopy. New optical technologies, when coupled with these new generations of detectors, provide powerful tools for plasma diagnostics and spectrochemical analysis [1,2]. An important advantage of the LIBS technique over classical methods stems from the possibility of in-situ analysis of virtually all types of materials (solids, liquids, molten materials, and gases) without the need for any sample preparation. In this presentation, we will give an overview on the development of the LIBS technique in the past, present and some perspectives for its future as analytical tool. Also, we will cover fundamental studies, analytical results and applications of LIBS related to the field of analytical chemistry, real time analysis and process control.
Exciting the S 1 and S 2 state directly : In the lp = 300 nm ex-
periment both the S 1 and the S 2 state can be excited by the pump pulse. Thus, the TRPE spectrum is expected to reflect dynamics evolving in both states in parallel. From a kinetics perspective, this would give rise to a bi-exponential decay. This is indeed observed. The fact that the decay-associated spectra are identical can be explained by ionization through an intermediate state, that is, the absorption of the first of the two probe-photons is resonant. Thus, the decay-associat- ed spectra are identical because they represent the PE spec- trum of the intermediate highly excited state. We assign the 340 fs to the lifetime of the S 2 state. The two long time con- stants, 13.5 and 400 ps, are assigned to the lifetime of the S1 state in the anti–anti and syn–anti conformer, respectively. This assignment is depicted schematically in Scheme 3, where, for simplicity, only sequential population of S1 is
time 〈t〉 is a relevant parameter to characterize the cases a 1 , b 1 , and b 2 , where the centroid of the ﬂuorophores is respectively equal to 14, 15, and 17 mm, but not adapted to relate the ﬂuorophore side spreading along the direction x (cases c 1 and c 2 ). Moreover the use of the second moment 〈ρ〉 shows that the inclusion size is 50–60% larger than the true value in the cases a 1 , b 1 , and b 2 , but is underestimated in the cases c 1 and c 2 . These conclusions are independent whether the beam is enlarged (d s ¼10 mm) or not (d s -0, like a point source). These results still conﬁrm that the diffusion process strongly contributes to enlarge the reconstructed size of objects having a spherical or cylindrical shape, from FWHM measurements  . In point of fact, no improvement was observed in the estimation of the lateral spreading of the ﬂuor- ophore distribution when the laser source was held ﬁxed closest to the axis (x s ¼0) of the object. As the ﬂuorescent inclusion laterally extends, only a volume of ﬂuorophores located around the axis of the source remains excited, thus generating ﬂuorescent remitted intensity proﬁles that give practically the same value of 〈ρ〉. It is reasonable to expect that measurements performed by using source–detector scanning arrangements will improve the ability to characterize the spreading size along the direction x. This is well conﬁrmed in Table 4 , where it is shown that scanning together the source–detector (x d ¼5 mm) along the scalp surface gives satisfac- tory results, although the time-gating mode may be more accurate than the continuous mode. Therefore, combining temporal (〈t〉) and spatial (scanning mode) measurements thus enhances the characterization of ﬂuorophore distribution as well as provides a means of distinguishing depth location and lateral extension of ﬂuorescence inside a complex head model.
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Laser-inducedfluorescence detection of lead atoms in a laser-induced plasma: an experimental analytical optimization study