Optical properties of new indotricarbocyanine dye as a limiter of laser radiation power

We present results of experimental and theoretical studies of the optical characteristics of a new indotricarbocyanine dye that is capable of effectively limiting the power of laser radiation in the visible spectral range. The spectral-luminescent and energy characteristics of the dye molecules and their absorption spectra from the excited state with nanosecond resolution are investigated experimentally. Quantum-chemical methods are used to calculate electronic absorption spectra from the ground (S₀ → S_n) and excited (S₁ → S_n) states and to determine the nature of electronic states of the molecule and the rate constants of intramolecular photophysical processes. The results of the theoretical research agree with experimental data. It is shown that the investigated dye has singlet-singlet absorption at 400–600 nm. Nonlinear absorption of the dye upon excitation by radiation of the second harmonic of a Nd:YAG laser is studied by z-scanning with an open diaphragm. The ratio of dye absorption cross sections from the excited and ground states at 532 nm is determined in the framework of a three-level model. The results are compared with those for previously studied compounds. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 473–480, July–August, 2007.     

A rich spectrum from potassium vapor on the 42 S 1/2−32 D 5/2 two-photon resonance

A rich emission spectrum in the wavelength range 300–600 nm, including 50 spectral lines, has been observed as a pulsed dye laser is tuned to the 4² S _1/2–3² D _5/2 two-photon resonance in potassium vapor. It is found that many kinds of mechanisms, including energy pooling, harmonic generation, quadrupole radiation, excitation transfer, and multiwave mixing etc., are involved in producing these lines. The process for each spectral line has been identified and is presented in tabular form.This project was supported by National Science Council of R.O.C. under the grant No. NSC 79-0208-M 009-21     

Decay Dynamics of 3‐methyl‐3‐pentene‐2‐one from the light absorbing S2(ππ*) state ‐ Resonance Raman Spectroscopy and CASSCF Study

The photophysics of 3‐methyl‐3‐pentene‐2‐one (3M3P2O) after excitation to the S₂(ππ*) electronic state were studied using the resonance Raman spectroscopy and complete active space self‐consistent field (CASSCF) method calculations. The A‐band resonance Raman spectra were obtained in cyclohexane, acetonitrile, and methanol with excitation wavelengths in resonance with the first intense absorption band to probe the structural dynamics of 3M3P2O. The B3LYP‐TD/6‐31++G(d, p) computation was carried out to determine the relative A‐band resonance Raman intensities of the fundamental modes, and the result was used to reproduce the corresponding fundamental band intensities of the 223.1 nm resonance Raman spectrum and thus to examine whether the vibronic‐coupling existed in Franck‐Condon region or not. CASSCF calculations were carried out to determine the minimal singlet excitation energies of S_{1, FC}, S_1,min (nπ*), S_{2, FC}, S_2,min (ππ*), the transition energies of the conical intersection points S_n/S_π, S_n/S₀, and the optimized excited state geometries as well as the geometry structures of the conical intersection points. The A‐band short‐time structural dynamics and the corresponding decay dynamics of 3M3P2O were obtained by the analysis of the resonance Raman intensity pattern and CASSCF computations. It was revealed that the initial structural dynamics of 3M3P2O was towards the simultaneous C₃=C₄ and C₂=O₇ bond elongation, with the C₃=C₄ bond length lengthening greater at the very beginning, whereas the C₂=O₇ bond length changing greater at the later evolution time before reaching the CI(S₂/S₁) conical intersection point. The decay dynamics from S₂(ππ*) to S₁(nπ*) via S₂(ππ*)/S₁(nπ*) in singlet realm and from S₁(nπ*) to T₁(nπ*) via ISC[S₁(nπ*)/T₂(ππ*)/T₁(nπ*)] in triplet realm are proposed. Copyright © 2014 John Wiley & Sons, Ltd.     

Observation of the ν3 Raman band of S3− inserted into sodalite cages

The S₃⁻ radical anion is observed in several systems: non‐aqueous polysulfides solutions, doped alkali halides, ultramarine pigments (UP) for which S₃⁻ is the blue chromophore and S₂⁻ is the yellow one and pigments of zeolite 4A structure. The S₃⁻ ion has C_2V symmetry, and therefore its three vibrational modes should be observed in the Raman and in IR spectra. In resonance Raman spectroscopy, only the symmetric stretching mode ν₁ and the bending mode ν₂ have been observed, whereas the anti‐symmetric stretching mode ν₃ has never been observed whatever the system. In this work, we confirm that ν₃ is not observed in solutions with resonance Raman spectroscopy. However, our investigation of several blue UP, with various concentrations of S₂⁻, shows that there is a superposition of two bands at ca 590 cm⁻¹: the first is assigned to ν (S₂⁻) and the second to ν₃ (S₃⁻). With the 457.9 nm excitation line, for which the resonance conditions are simultaneously fulfilled for S₂⁻ and S₃⁻, the band at ca 590 cm⁻¹ is the sum of the contributions of both ν (S₂⁻) and ν₃ (S₃⁻) vibrations, while, with the 647.1 nm line, which only satisfies the resonance conditions of S₃⁻, the band at ca 584 cm⁻¹ must be assigned only to ν₃ (S₃⁻). Furthermore, ν₃ (S₃⁻) is observed in green UP and in pigments of zeolite structure. The ν₃ vibration of S₃⁻, which is observed neither in polysulfide solutions nor in doped alkali halides in resonance Raman conditions, can therefore be observed when this species is inserted into the β‐cages of the sodalite or of the zeolite 4A structures. So, the band at ca 590 cm⁻¹ cannot always be assigned to S₂⁻ in these systems. This implies that the concentration of S₂⁻ in UP must be reconsidered. Copyright © 2007 John Wiley & Sons, Ltd.     

Theoretical analysis of S1-state lifetime measurements of dyes with picosecond laser pulses

Various methods for the determination of the S₁-state lifetime of dye solutions (laser dyes and modelocking dyes) are analysed. A general model of interaction of laser light with dye molecules is presented and reduced to a dye energy level scheme of six levels. Fluorescence emission, light amplification and absorption recovery techniques are investigated theoretically and their limitations revealed. The determination of the S₁-state lifetime of saturable absorbers by single picosecond pulse bleaching experiments is very thoroughly discussed. The influence of various laser and dye parameters on the bleaching experiments are analysed numerically. The results are compared with isotropic steady state two- and three-level dye models.     

Photophysical and laser characteristics of pyrromethene 567 dye: Experimental and theoretical studies

Narrow-band laser performance of alcohol solutions of pyrromethene 567 (PM567) and rhodamine 6G (RH6G) dye was investigated using a home-made GIG-configured dye laser, excited by the second-harmonic radiation (at 532 nm) of a pulsed Nd:YAG laser. Higher laser efficiency was observed with PM567 dye (∼23% peak) in comparison to the commonly used RH6G dye (16.5%), in spite of much lower fluorescence quantum efficiency of the PM567 (0.83) vis-à-vis RH6G (0.98) dye solutions in ethanol. First principle-based electronic structure calculations were performed on PM567 dye in the ground (S ₀) and excited states (S ₁) using density functional theory to elucidate the structure and photophysical properties of the dye.     

Electroproduction of η mesons in the region of the resonanceS 11(1535) at momentum transfers of 2 and 3 GeV2

We report on results of η-electroproduction in the resonance region at momentum transfers ofQ ²=2 GeV² and 3 GeV². The differential cross sections obtained in the region of the second nucleon resonance strongly support the dominance of theS ₁₁(1535) in this channel. The total transverse virtual photoproduction cross section of theS ₁₁(1535) shows a flatQ ²-dependence ～e ^?0.39· Q ². Comparison with the total resonant γ _v p cross section in the second resonance region aroundW=1.5 GeV shows that theD ₁₃(1520) production decreases much faster (～e ^?1.6· Q ²). The data are not compatible with the simple harmonic oscillator quark model with spin and orbit excitation of a quark only.     

Direct magnetoelectric effect in two-layer composite structures Tb0.12Dy0.2Fe0.68-PbZr0.53Ti0.47O3 at bending and longitudinal vibrations

The direct magnetoelectric effect has been studied in samples of two-layer composites containing 8 × 6 × 0.3-mm layers of the piezoelectric material PbZr_0.53Ti_0.47O₃ and 6 × 6 × A-mm layers (A = 0.3, 0.6, 0.9, 1.2, and 1.5) of the ferromagnet Tb_0.12Dy_0.2Fe_0.68 and epoxy adhesive in the frequency range of 10–253 kHz at room temperature. It has been found that the magnetoelectric effect significantly increases at resonance frequencies (13.2–61.1 kHz) of the first harmonic of bending vibrations along the sample length, at resonance frequencies (39.5–90.7 kHz) of the first harmonic of bending vibrations along the sample width, and at resonance frequencies (123.3–141.0 kHz) of the first harmonic of longitudinal vibrations along the sample length. The magnetoelectric effect magnitudes at the resonance frequencies of the bending vibrations is found to be greater than that at the resonance frequencies of the longitudinal vibrations of the sample.     

Absorption and resonance Raman spectroscopy of the 1Bu state of trans‐1,3,5‐hexatriene including vibronic coupling

The vibronic coupling between the first excited S₁ (2¹A_g) and the second excited S₂ (1¹B_u) singlet electronic states in spectroscopy of trans‐1,3,5‐hexatriene molecule is investigated on the basis of a model consisting of two electronic states coupled by two vibrational modes. Employing a perturbation theory that treats the intramolecular couplings in a perturbative manner, the absorption and resonance Raman cross sections and excitation profiles of this molecule are calculated using the time‐correlation function formalism. The non‐Condon corrections are included in evaluation of cross sections. The multidimensional time‐domain integrals that arise in these calculations have been evaluated for the case in which S₀ (1¹A_g) S₂ (1¹B_u) electronic transition takes place between displaced and distorted harmonic potential energy surfaces. The calculated spectra are in good agreement with the experimental ones. Copyright © 2011 John Wiley & Sons, Ltd.     

Features of laser-induced luminescence and photoconductivity of layered Cu<Subscript>3</Subscript>In<Subscript>5</Subscript>S<Subscript>9</Subscript> crystals

Luminescence and photoconductivity of layered Cu₃In₅S₉ crystals at high levels of optical excitation are studied experimentally. A pulsed nanosecond Nd:YAG laser with built-in second and third harmonic generators to generate 1064-, 532-, and 355-nm radiation is used as a light source. It is found that the photoluminescence spectra exhibit two emission bands due to zone–acceptor level and impurity donor–impurity acceptor transitions. It is shown that the photoconductivity in Cu₃In₅S₉ is monopolar. The waveform of the photoconductivity consists of fast and slow components associated with two channels of recombination.     

Surface second harmonic generation from coumarin 343 dye-attached TiO<Subscript>2</Subscript> nanoparticles at liquid–liquid interface

The nonlinear optical properties of coumarin 343 (C343) dye-attached TiO₂ nanoparticles in the size range 5–8 nm adsorbed at the interface of water/1,2-dichloroethane have been studied by using the surface second harmonic generation technique. No second harmonic (SH) response was observed from the bare TiO₂ nanoparticles adsorbed at the interface, however, a strong SH response was measured from the dye molecules attached at the surfaces of the nanoparticles. The increase in the SH intensity with the increase of TiO₂ nanoparticle concentration in the aqueous solution of C343 is mainly due to the pre-alignment of the dye molecules at the surfaces of nanoparticles and is partly due to the third-order polarization contribution of the nanoparticles to the observed total SH response.     

Development of coherent tunable source in 2–16 μm region using nonlinear frequency mixing processes

A very convenient way to obtain widely tunable source of coherent radiation in the infrared region is through nonlinear frequency mixing processes like second harmonic generation (SHG), difference-frequency mixing (DFM) or optical parametric oscillation (OPO). Using commonly available Nd:YAG laser and its harmonic pumped dye laser radiation as parent beams, we have been able to generate coherent tunable infrared radiation (IR) in 2–16 μm region using different nonlinear crystals by DFM and OPO. We have also generated such IR source in the 4–5 μm region through SHG of CO₂ laser in different infrared crystals. In the process we have characterized a large number of nonlinear crystals like different borate group of crystals, KTP, KTA, LiIO₃, MgO:LiNbO₃, GaSe, AgGaSe₂, ZnGeP₂, AgGa_1?x In _x Se₂, HgGa₂S₄ etc. To improve the conversion efficiencies of such frequency conversion processes, we have developed some novel schemes, like multipass configuration (MC) and positive optical feedback (POF). The significance of the obtained results lies in the fact that to get the same conversion in SHG or DFM, one now requires fundamental input radiation with much lower intensity.     

Structural dynamics of 4‐cyanobenzaldehyde in S2(ππ*) state

The excited state structural dynamics of 4‐cyanobenzaldehyde (p‐CNB) were studied by using the resonance Raman spectroscopy and the quantum mechanical calculations. The experimental A‐ and B‐band absorptions were, respectively, assigned to the major n_O → π₃* and π₂ → π₃* transitions according to the B3LYP‐TD/6‐31G(d) and CIS/6‐31G(d) computations, and the resonance Raman spectra. It was determined that the actual S₂(π₂π₃) state was in energy lower than S₃(π₁π₃), which was just opposite to the B3LYP‐TD/6‐31G(d) calculated order of the S₂(π₁π₃) and S₃(π₂π₃). The vibrational assignments were carried out for the A‐ and B‐band resonance Raman spectra. The B‐band resonance Raman intensities of p‐CNB were dominated by the C2–C3/C5–C6 symmetric stretch mode ν₈, the overtones nν₈ and their combination bands with the ring C–H bend mode ν₁₇, the C9–N10 stretch mode ν₆, the C7–O8 stretch mode ν₇ and the remaining modes. The conical intersection between S₁(n_Oπ₃) and S₂(π₂π₃) states of p‐CNB was determined at complete active space self‐consistent field (CASSCF)(8,7)/6‐311G(d,p) level of theory. The B‐band short‐time structural dynamics and the corresponding decay dynamics of p‐CNB were obtained by analysis of the resonance Raman intensity pattern and CASSCF computations. The resonance Raman spectra indicated that CI[S₁(n_Oπ₃)/S₂(π₁π₂π₃π₄)] located nearby the Franck–Condon region. The excited state decay dynamics evolving from the S_{2, FC}(π₂π₃) to the S₁(n_Oπ₃) state was proposed. Copyright © 2013 John Wiley & Sons, Ltd.     

Two-photon excitation of Na atoms in a flame by broad-band laser irradiation

With a flashlamp-pumped tunable dye laser the 3S→3D, 3S→4D and 3S→5S two-photon transitions of sodium are excited and the resulting fluorescence radiation at various atomic transitions is detected. The sodium is nebulized into a stoichiometric H₂-O₂-Ar flame at atmospheric pressure and at a temperature of 1800 K. Collisional population exchange between several of the higher Na-levels is found to occur. Saturation and saturation broadening of two-photon transitions are observed. Formulas for two- photon excitation rates in the case of broad-band excitation are derived and show substantial agreement with experiment.     

A‐band structural dynamics of thioanisole by resonance Raman spectroscopy

The structural dynamics of thioanisole in the S₂(ππ*) electronic state that has large oscillator strength was studied by using the resonance Raman spectroscopy. The vibrational assignments were done for thioanisole on the basis of the FT‐Raman and FT‐IR measurements, the density‐functional theory computations and the normal mode analysis. The A‐ and B‐band resonance Raman spectra were obtained in cyclohexane, methanol and acetonitrile, in which ten modes in A’ irreducible representations were observed. The structural dynamics were obtained according to the resonance Raman intensity pattern. The vibroinc‐coupling between the S₃(πσ*) electronic state that has no oscillator strength and the S₂(ππ*) electronic state were revealed. We discuss the correlation between our present structural dynamics and the previous S₂(ππ*)/S₃(πσ*) conical intersectional dynamics revealed by resonant‐enhanced two‐photon ionization and the photofragment excitation spectroscopic study. Copyright © 2012 John Wiley & Sons, Ltd.     

The excited state dynamics study of di‐2‐pyridylketone in the A‐band and B‐band absorptions by using resonance Raman spectroscopy,IR and UV–visible spectroscopy

Excitation wavelengths of 282.4, 273.9 (A band), 252.7, 239.5 and 228.7 nm (B band) resonance Raman spectra were acquired for di‐2‐pyridylketone, and density functional calculations were carried out to help in the elucidation of the photo relaxation dynamics of A‐band and B‐band electronic transitions. The resonance Raman spectra show that the intensity pattern of the A band presents great difference from that of the B band, which indicate that the short‐time A‐band (S₀→S₄) photo relaxation dynamics have substantial difference from that of B band (S₀→S₁₀) . The overall picture of short‐time dynamics and the vibronic coupling mechanisms are interpreted using Albrecht's theory. Copyright © 2012 John Wiley & Sons, Ltd.     

Fast photoprocesses in a symmetric indotricarbocyanine dye (HITC) in solutions

Spectral-kinetic and photochemical properties of HITC dye with iodide and perchlorate counterions have been studied in environments where the dye molecules exist in different ionic forms. In ethanol, the dye molecules exist as free ions; in dichlorobenzene, as contact ion pairs. Superfast transformation of non-stationary spectra in an HITC dye bleaching band is found. The observed effects are interpreted within the framework of concepts on “burning out” a notch in the contour of a non-uniformly widened vibronic band of S ₀ → S ₁-absorption. Qualitative differences in recorded absorption spectra from the dye excited electronic states for weakly and highly polar solvents are found. It is shown that the observed differences are caused by superfast charge transfer in the contact ion pairs that results in the formation of free radicals.     

Lifetime measurements in the triplet system of Mg I

In an atomic beam the metastable 3s3p ³ P-states of Mg I were populated by electron impact. A pulsed tunable dye laser was used to excite the metastable atoms to the 3snd³ D-(n=3–7) and to the 3sns³ S ₁-states (n=4and 6). Observing the time dependence of the reemitted resonance light the lifetimes of these states were measured.     

Sum-frequency generation in a cooledβ-BaB2O4 crystal

Sum-frequency generation in -BaB₂O₄ has been studied by mixing the unpolarized output of an excimer laser pumped dye laser with its second harmonic. The shortest wavelength obtained at 95 K is 195.3 nm. A lower limit of 194.4±0.2 nm at the temperature of liquid helium can be expected.     

Giant Gamow-Teller resonance: 40 Years after the prediction

A brief survey of the physics of the giant Gamow-Teller resonance, from the history of its prediction and the first attempts at theoretically describing it to the present-day state of this realmof nuclear physics, is given. The structure of Gamow-Teller resonances is analyzed within the theory of finite Fermi systems. Simple expressions for the energy of the Gamow-Teller resonance and for the matrix elements of its excitation are derived via approximately solving the equations of this theory by the semiclassicalmethod. The calculated values of the energy difference between the Gamow-Teller resonance and the analogous resonance are found to be in good agreement with their experimental counterparts. Strength functions for the beta decay of neutron-rich nuclei, S _β (E), are analyzed, and the calculated values of S _β (E) are contrasted against relevant experimental data.