Excited-state Cross Sections Research Articles

Nanobelt and nanoplatelet structured molybdenum disulfide thin film as a saturable absorber under nanopulsed green laser excitation

Demonstration of saturable absorption (SA) in MoS2 thin films with varying NLO coefficients as a function of reaction time of hydrothermal method is made using the open aperture Z-scan technique. Under nanosecond pulsed laser excitation (532 ​nm, 9 ns, 10 HZ), saturable absorption occurred involving the overtone of electron - hole pair state and band edge state of MoS2. Further higher ground state cross-section than excited state cross-section favors SA process in MoS2 thin films. The strong saturable absorption behaviors of nanobelt like structured MoS2 film could be attributed to the coexistence of 1T and 2H crystal phases and lower dimension morphology that allows more photons to transit to the higher energy state. Earlier the fabrication of MoS2 thin film on a FTO substrate with a varying reaction time of the hydrothermal technique such as 24, 36, 48 and 60 ​h was made. Raman spectrum has two sets of characteristics vibration representing the metallic 1T – octahedral coordination Oh phase and the semiconducting 2H – trigonal prismatic D3h phase. XRD and Raman studies confirm the formation of mixed phases of MoS2 with 1T phase dominating over 2H phase in MoS2 thin films. Here the absorbance and band gap of the MoS2 thin film increased with increase in reaction time. The luminescence spectra exhibit prominent peaks at 594 ​nm and 621 ​nm resulting from a direct bandgap transition and they are mostly due to the VBM splitting at the K-point. All the films exhibit maximum absorbance in the UV region (291 ​nm) due to the excitonic features of MoS2 and notable absorbance in the visible region (680 ​nm) due to the overtones of MoS2 ‘s electron-hole pair. SEM images confirm that nanoplatelet and nanobelt structured MoS2 was formed with varying size with respect to reaction time. Furthermore, while the nanoplatelet structure faded, nanobelts were grown for a prolonged reaction time. Thus, MoS2 nanostructure coated thin film would be useful for the design of saturable absorbers for fabricating optical switches and mode locking devices.

Implications of morphology on excited state absorption of α-MnO2 nanostructures

Nanoclusters, nanorods and nanowires of α-MnO2 were synthesized by reduction method at different annealing temperature (100 °C–500 °C). X-ray diffraction and Raman studies confirms the formation of pure tetragonal phase of α-MnO2. Surface morphology using SEM and HRTEM reveals the gradual transformation of α-MnO2 nanoclusters (100 °C–300 °C) to nanorods (400 °C) to well defined nanowires (500 °C). While increasing the annealing temperature, Ostwald ripening process initially withholds the agglomerated clusters and its size get reduced and fused that leads to orientation along particular direction. HRTEM clearly displays the influence of temperature on favoured growth plane where (411) of nanoclusters changed to (211) plane of nanorods and nanowires. Optical band edge absorption at 268 nm arising from d–d transitions of Mn4+ in MnO2 got blue shifted due to variations in morphology. Here with increase in temperature, aspect ratio increases which alters the number of surface atoms and consequently the cohesive energy put on effect in the widening of bandgap of the material from 4.31 eV (nanoclusters) to 4.63 eV (nanowires). Open aperture Z-scan technique using Nd: YAG laser (532 nm, 10 Hz & 9 ns) revealed all MnO2 nanostructures involve reverse saturable absorption ascribed due to excited state absorption and its strength varies with morphology. Significant absorption in the visible region (532 nm) provoked excited state absorption and intensity dependent variation of nonlinear absorption coefficient confirms the existence of sequential two photon absorption process. α-MnO2 nanowires with extended interconnected network and larger aspect ratio exhibits wider excited state cross-section (6.64 × 10−2 GM), higher two-photon absorption coefficient (2.01 × 10−10 m/W) and lower onset optical limiting threshold (2.13 × 1012 W/m2). This stronger optical limiting performance of α-MnO2 nanowires symbolizes the scope of utilizing optimal α-MnO2 nanostructure for optical limiting applications.

Crystal structure, linear and nonlinear optical properties of three thiophenyl chalcone derivatives: A combined experimental and computational study

Abstract Three thiophenyl chalcone derivatives, (E)-1-(5-bromo-2-thienyl)-3-(4-bromophenyl)prop-2-en-1-one (B5B2SC), (E)-1-(5-bromo-2-thienyl)-3-(3-chlorophenyl)prop-2-en-1-one (3C5B2SC), and (E)-1-(5-bromo-2-thienyl)-3-(2-methoxyphenyl)prop-2-en-1-one (2M5B2SC), were successfully synthesized and crystallized. The structures were confirmed by experimental and theoretical FTIR and 1H NMR spectra. The crystal structures were determined by single-crystal XRD method. The B5B2SC, 3C5B2SC and 2M5B2SC crystallize in the monoclinic space groups P 21/c (centrosymmetric), P 2 (non-centrosymmetric) and triclinic space group P 1 ‾ (centrosymmetric), respectively. All these structures adopt trans configuration with respect to C6═C7 double bond. The chalcones have high thermal stability, a wide transparency in the visible region and small optical band gaps. The 3C5B2SC exhibits powder second-harmonic generation (SHG) intensity of about 1.7 times higher than Urea. From continuous wave (CW) laser (532 nm) Z-scan experimental data analyses, the third-order NLO parameters such as nonlinear absorption coefficient (β = ~10−4 cm/W), nonlinear refractive index (n2= ~10−9 cm2/W), third-order NLO susceptibility (χ(3) = ~10−7 esu), molecular hyperpolarizability (γh = ~10−27 esu), ground state absorption cross section (σg = ~10−22 cm2) and excited state cross sections (σex= ~10−20 cm2) were determined. The chalcones also exhibited optical limiting and all optical switching behaviour for CW laser operating at 532 nm wavelengths. The electric dipole moment, polarizability, hyperpolarizabilty, HOMO-LUMO energy gap, global chemical reactivity descriptors (GCRD), molecular electrostatic potentials (MEP) and natural bond orbital (NBO) analysis were computed theoretically (DFT). The results indicate that these three chalcones with thiophene moiety are potential materials for optical device applications.

Configuration mixing in 12,14O and the 14O(p, t) reaction

In two-neutron pickup from 14O, the calculated cross-section ratio for the first two 0+ states of 12O depends on the configuration mixing in these two states, and on the amount of core excitation in the ground state (g.s.) of 14O. Using mirror symmetry and 12Be wave functions that are reasonably well known, I have calculated this ratio as a function of the core excitation in 14O(g.s.). Results suggest that the excited-state cross section from a recent measurement is too large.

Electrochemical and non-linear optical behavior of a new neodymium double-decker phthalocyanine

This manuscript presents the non-linear optical parameters obtained specifically at 532nm using the new bis-{1(4),8(11),15(18),22(25)-(tetrapyridin-3-yloxy) phthalocyaninato} neodymium(III) complex in green (2a) and blue (2b) forms as well thin films prepared from the green form in the presence of poly(bisphenol A) carbonate. It is interesting to note a huge improvement of the reduction efficiency of transmission of the green form by 34% in poly(bisphenol A) carbonate as a thin film. The same observation is noted for the blue form at 25%. The same trend was observed for the excited state cross sections in which the blue form of the bis-{1(4),8(11),15(18),22(25)- (tetrapyridin-3-yloxy) phthalocyaninato} neodymium(III) complex as well as the thin film exhibited values that were about three and six times greater than those of the green form, respectively. The electrochemical properties were also studied, with complex 2a exhibiting six redox processes in DCM, by employing tetrabutylammonium tetrafluoroborate as an electrolyte.

Tetracarboxy-phthalocyanines: From excited state dynamics to photodynamic inactivation against Bovine herpesvirus type 1

Herein we present the excited state dynamic of zinc and aluminum tetracarboxy-phthalocyanines (ZnPc and AlPc) and its application in the photodynamic inactivation (PDI) of Bovine herpesvirus type 1 (BoHV-1) in vitro. The excited state dynamic provides valuable data to describe the excited state properties of potential optical limiters and/or photosensitizers (PSs), such as: the excited state cross-sections, fluorescence lifetime and triplet state quantum yield. The excited state characterization was performed using three different Z-scan techniques: Single Pulse, White Light Continuum and Pulse Train. Considering the photodynamic inactivation of BoHV-1, an initial viral suspension containing 105.75TCID50/mL was incubated with the PSs for 1h at 37°C under agitation and protected from light. The samples were placed in microtiter plates and irradiated (180mW/cm2). During irradiation, a sample was taken every 15min and the viability of the virus was evaluated. The results show that both phthalocyanines were efficient against viruses. However, a higher photodynamic efficiency was observed by ZnPc, which can be attributed to its higher triplet and singlet quantum yields. The results presented here are important for animal health (treatment of BoHV-1) and also open up a field of studies to use AlPc and ZnPc as potential agents against a wide range of microorganisms of veterinary interest.

Optical nonlinearities of tetracarbonyl-chromium triphenyl phosphine complex

The new tetracarbonyl — chromium-triphenyl phosphine complex was synthesized and characterized using ultraviolet (UV)–visible, Fourier transform infrared (FTIR), and nuclear magnetic resonance (NMR) techniques. The characterization results confirm the molecular structure of the new complex. The z-scan measurements were done by diode laser [continuous wave (CW)] to estimate the nonlinear optical parameter (χ3). The results led to calculate three parameters: the ground-state cross sections (), the excited-state cross sections (), and thermo–optic coefficient of the new complex. This study indicated that our complex is a suitable for photonic applications.

High-resolution measurements of the exited states (n,pn), (n,dn) C-12 cross sections

Measurements of C12 cross sections for the excited states (n,p 0 ) up to (n,p 4 ) and (n,d 0 ), (n,d 1 ) have been carried out. The Van de Graaff neutron generator of the EC-JRC-IRMM laboratory has been used for these measurements. A very thin tritiated target (263 μg/cm 2 ) was employed with deuteron beams energies impinging on the target in the range 2.5–4.0 MeV. Neutrons in the range 18.9–20.7 MeV were produced with an intrinsic energy spread of 0.2–0.25% FWHM. With such narrow neutron energy spread, using a high energy resolution device such as a single crystal diamond detector, several peaks from the outgoing charged particles produced by the (n,p n ), (n,d n ) and also (n,α 0 ) reactions appear in the pulse height spectrum. The peaks can be identified using the reaction Q-values. The diamond detector used for these measurements has shown an intrinsic energy resolution lower than 0.9% FWHM. The analysis of the peaks has permitted to derive the partial carbon reaction cross sections for several excited states. The results are presented in this paper with the associated uncertainties and they are compared with different versions of TENDL compilation when these data are available (e.g. versions 2009, 2010, 2011 and 2015) and also with experimental results available in the EXFOR database.

Nonlinear optical characterization of multinuclear iridium compounds containing tricycloquinazoline.

Nonlinear optical properties were characterized for a series of multinuclear iridium compounds of the form TCQ[IrIII(ppz)2]n, where n=1, 2, or 3, TCQ is tricycloquinazoline, and ppz is 1-phenylpyrazole. Transient absorption (TA) spectroscopy indicated that the triplet metal-to-ligand charge transfer excited state was formed on a subpicosecond time scale and decayed back to the ground state on a microsecond time scale, consistent with precedents in the literature. TA bands were observed for all three compounds from 475 to 900nm, implying the potential for reverse-saturable absorption (RSA) at those wavelengths. Z-scan measurements using picosecond and nanosecond pulses were obtained at 532nm and confirmed the presence of RSA behavior for all three compounds. The triplet excited state cross sections and the RSA figure of merit were found to decrease with increasing n:1>2∼3.

Recoil distance transmission method: Measurement of interaction cross sections of excited states with fast rare-isotope beams

The possible appearance of nuclear halos in ground and excited states close to the particle-decay threshold is of great importance in the investigation of nuclear structure and few-body correlations at the limit of stability. In order to obtain direct evidence of the halo structure manifested in nuclear excited states, we have considered a new method to measure the interaction cross sections of excited states. The combination of the transmission method and the recoil distance Doppler-shift method with a plunger device enables us to measure the number of interactions of the excited states in a target. Formulae to determine the interaction cross section are derived, and key issues to realize measurements are discussed. Dominant sources of errors are uncertainties in the excited-state lifetimes and γ-ray yields. We examine prototype experiments and perform simulations to study the impact of each uncertainty on the final result. This method provides a novel opportunity to perform cross section measurements on the excited states of rare isotopes.

One-neutron stripping processes to excited states of theLi6+Zr96reaction at near-barrier energies

We report the measurement of one-neutron stripping to excited-state cross sections from the weakly bound projectile $^{6}\mathrm{Li}$ to the $^{96}\mathrm{Zr}$ target at near-barrier energies by the online $\ensuremath{\gamma}$-ray spectroscopy method. Transitions of the $^{97}\mathrm{Zr}$ nucleus were clearly identified by $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidences. This cross section was found to be much smaller than the previously reported complete-fusion cross section for this system at energies above the barrier, whereas it becomes of the same magnitude around the Coulomb-barrier energy. No evidence of two-neutron transfer was found. We also performed coupled reaction channel calculations for the one-neutron stripping process. The calculation results are discussed.

Strong triplet excited-state absorption in a phenanthrolinyl iridium(III) complex with benzothiazolylfluorenyl-substituted ligands

Femtosecond transient difference absorption (fs TA) measurements, together with a series of open-aperture Z scans at picosecond and nanosecond pulse widths and a variety of pulse energies, were performed on a 1,10-phenanthrolinyl iridium(III) complex bearing ligands containing a benzothiazolylfluorenyl motif. An analysis of decay data from the fs TA experiment yields a value of 1.24±0.26 ns for the singlet excited-state lifetime τ(S) of the complex. By fitting the Z scans to a five-level dynamic model incorporating the independently measured value of τ(S) and previously reported values of the complex's triplet quantum yield (0.13) and triplet excited-state lifetime (230 ns), we obtain values of 3.5×10(-17) cm(2) (singlet) and 5.0×10(-16) cm(2) (triplet) for the excited-state absorption cross-sections of the complex in toluene solution at 532 nm; the latter value represents one of the largest triplet excited-state absorption cross-sections ever reported at this wavelength. The ratio of the triplet excited-state cross-section to the ground-state absorption cross-section exceeds 3800.

Fluorescence and Judd-Ofelt Analysis of Er<sup>3+</sup> Doped CaF<sub>2</sub> Transparent Ceramic

In this paper, we evaluated the spectra parameters of Er3+.The absorption spectra of Er3+:CaF2transparent ceramic was measured at room temperature (RT). Based on the Judd–Ofelt theory, the intensity parameters were Ω2= 5.02×10−20cm2, Ω4= 3.40×10−20cm2and Ω6= 0.38×10−20cm2, and then the values of the radiative transition probabilities, radiative lifetimes and integrated emission cross-sections of excited states were calculated. Full width at half maximum (FWHM) of the fluorescence spectra for4I13/2→4I15/2transition was investigated, being 17nm. The decay time was found to be 24.3ms, which is longer than the theoretically calculated value indicating a radiation trapping effect in this work.

Elastic and inelastic scattering of 6Li + 18O versus 7Li + 18O and 6Li + 16O

Inverse kinematics scattering of 18 O on 6 Li at E lab ( 18 O) = 114 MeV was measured to obtain elastic and inelastic scattering cross sections. In this way cross sections for excited states in 6 Li and 18 O were determined. The data were analyzed within the optical model and coupled reaction channel method. The 6 Li + 18 O optical potential as well as the 6 Li and 18 O deformation parameters were deduced. Contributions of different nuclear processes to the 6 Li + 18 O elastic and inelastic scattering were explored. The isotopic differences between the 6,7 Li + 18 O and 6 Li + 16,18 O potential parameters were determined.

Formation of antihydrogen in an antiproton-positron Debye plasma in the presence of an external laser field

We study quantum mechanically the influence of an external laser field on the antihydrogen ($\overline{\mathrm{H}}$) formation cross sections in ground and excited states (2$s$,2$p$) via the three-body recombination process inside a dense plasma of antiprotons and positrons, supposed to be the most efficient mechanism for cold and trapped antihydrogen. The plasma screening is considered in the framework of a Debye- H\"uckel potential. The laser polarization is chosen to be parallel to the incident momentum of the passive positron. The modifications due to the presence of the laser field are found to be quite significant both quantitatively and qualitatively for all the states. In the presence of a laser, the $\overline{\mathrm{H}}$ formation cross sections are found to be suppressed significantly with respect to the field-free situation particularly in the ground state, while the excited state cross sections are in general enhanced at very low incident energies but are again suppressed at higher energies except for some special cases. The sensitivity of the formation cross sections with respect to the Debye length are also studied both in the laser-assisted and in the field-free situations. At very low incident energies, the ground state multiphoton formation is found to enhance with the increase in Debye screening, while the reverse is true for the excited states. These findings should have important implications for future $\overline{\mathrm{H}}$ studies.

Study on third-order nonlinear optical properties of 4-methylsulfanyl chalcone derivatives using picosecond pulses

In this paper we present results from the experimental study of third-order nonlinear optical (NLO) properties of three molecules of Br and NO2 substituted chalcone derivatives namely (2E)-1-(4-bromophenyl)-3-[4(methylsulfanyl)phenyl]prop-2-en-1-one (4Br4MSP), (2E)-1-(3-bromophenyl)-3-[4-(methylsulfanyl) phenyl]prop-2-en-1-one (3Br4MSP) and (2E)-3[4(methylsulfanyl) phenyl]-1-(4-nitrophenyl)prop-2-en-1-one (4N4MSP). The NLO properties have been investigated by Z-scan technique using 2ps laser pulses at 800nm. The nonlinear refractive indices, nonlinear absorption coefficient, and the magnitude of third-order susceptibility have been determined. The values obtained are of the order of 10−7cm2/GW, 10−3cm/GW and 10−14esu respectively. The molecular second hyperpolarizability for the chalcone derivatives is of the order of 10−32esu. The coupling factor, excited state cross section, ground state cross section etc. were determined. The optical limiting (OL) property was studied. The results suggest that the nonlinear properties investigated for present chalcones are comparable with some of the reported chalcone derivatives and can be desirable for NLO applications.

Synthesis, tunable two and three-photon absorption properties of triazine derivatives by branches

Three novel triazine derivatives, (E)-4-(2-(4,6-dimethyl-1,3,5-triazin-2- yl)vinyl)- N,N-di-p-tolylaniline (a), 4,4′–((1E,1′E)-(6-methyl-1,3,5-triazine-2,4-diyl) bis(ethene-2,1-diyl))bis(N,N-di-p-tolylaniline) (b), and 4,4′,4′′–((1E,1′E,1′′E)-(1,3,5- triazine-2,4,6-triyl)tris(ethene-2,1-diyl))tris(N,N-di-p-tolylaniline) (c), were designed and synthesized. Their photophysical and photochemical properties were investigated systematically including single-photon absorption, nonlinear optical absorption (NOA) and up-converted fluorescence. Interestingly, the compound a with single branch showed pure three-photon absorption phenomenon, while the corresponding b and c indicated two-photon induced excited-state absorption properties, showing strong structure-dependence relationship. The results offer a method to design and synthesize organic molecules for multiphoton materials. It was noted that the three-photon cross-section value (δ3) of a was up to 1.35 × 10−76 cm6 s2. Correspondingly, the two-photon (δ2) and excited-state cross-section (δe) values of b and c also were obtained, and value of them were 485 GM and 1.03 × 10−17 cm2 for b, and 1100 GM and 1.27 × 10−18 cm2 for c, respectively.

Electron-impact ionization of C+excited states

Nonperturbative close-coupling and perturbative distorted-wave methods are used to calculate electron-impact ionization cross sections for excited states of C${}^{+}$. Both the time-dependent close-coupling and the time-independent distorted-wave methods are used to calculate direct ionization cross sections for the $1{s}^{2}2{s}^{2}3l$ configurations. An $R$ matrix with pseudostates method is used to calculate total ionization cross sections for the $1{s}^{2}2{s}^{2}3l$ configurations, including both direct and indirect excitation-autoionization contributions. Comparison of the results shows both a substantial reduction of the direct ionization cross sections due to nonperturbative effects and a large contribution to the total ionization cross sections due to indirect contributions coming from $2s\ensuremath{\rightarrow}2p$ excitations. The ionization cross-section results will permit the generation of more accurate generalized collisional-radiative ionization coefficients needed for the modeling of moderately dense carbon plasmas.

Observation of tunable two-photon induced excited-state and three-photon absorption phenomena by structure in oligomerfluorene derivatives

The nonlinear optical properties, including two-, three-photon and excited-state absorption phenomena, were observed in three oligomerfluorene derivatives (abbreviated as OF3, OF5 and OF7) by femtosecond (450 fs) laser pulses. Their two-, three-photon and, excited-state absorption properties were studied by open Z-scan and pump-probe measurements. Interestingly, when the numbers of fluorene units increased from 3 to 5, and to 7, the corresponding absorption phenomena changed from three-photon to two-photon induced excited-state phenomena, showed strong structure dependence in these derivatives. The results offer a method to design and synthesize organic molecules for multiphoton materials. It was noted that the three-photon cross-section value (δ 3) of OF3 was up to 1.36×10−76 cm6 s2. Correspondingly, the two-photon (δ 2) and excited-state cross-section (δ e ) values of OF5 and OF7 also were obtained, and they were 1230 GM and 0.91×10−18 cm2 for OF5, and 1780 GM and 1.18×10−18 cm2 for OF7, respectively.

Electron-impact ionization of moderately charged atomic ions in excited states

Nonperturbative $R$-matrix and perturbative distorted-wave methods are used to calculate electron-impact ionization cross sections for ${\mathrm{C}}^{3+}$ in excited states. Convergence studies for the cross sections of the $1{s}^{2}5s$ excited configuration reveal that both the $R$-matrix and distorted-wave methods need fairly high ejected electron angular momenta. Reasonable agreement is found between the converged $R$-matrix and distorted-wave cross sections. Thus, the use of the computationally less demanding distorted-wave method as a tool for the $n$ scaling of excited-state ionization cross sections appears to be reasonable for atomic ions with charge $q\ensuremath{\geqslant}3$.