9,10-Anthracene-centered oligo(p-phenyleneethynylene)s with end-capping didecylamines exhibiting enhanced two-photon fluorescence action cross-section

This study reports the synthesis and the two-photon absorption (TPA) properties of a series of 9,10-anthracene-centred oligo(p-phenyleneethynylene)s with end-capping didecylamine. The results show that both the maximal TPA cross-sections (δ_max) and the fluorescence quantum yields (Φ) of the oligomers increase with the extension of phenylethynyl bridges. Interestingly, the Φδ_max per repeating unit to is obviously enhanced by extending linearly conjugation size of the oligomers. Moreover, these oligomers all show the maximal two-photon absorption cross-sections at 800 nm and emit strong green to yellowish-green two-photon excited fluorescence. These materials may find applications in which two-photon excited fluorescence and photo-induced electron transfer are utilized.     

Two-photon excitation spectrum of benzonitrile vapour

The two-photon excitation spectrum of benzonitrile in the gas phase at about 1 torr has been recorded and analysed in the total energy region of 36300 to 40500 cm⁻¹ using both linearly and circularly polarised light from a Nd-YAG pumped dye laser. The two-photon spectrum consists of strong Franck Condon (fc) transitions bearing a good resemblance to the one-photon spectrum and also vibronic coupling (vc) transitions essentially arising out of the analogue of the benzeneν ₁₄. By a comparative study of thetp spectra of various other monosubstituted benzenes, it has been inferred that the strongtp spectrum of benzonitrile should be ascribed to a considerableπ charge delocalization over the phenyl and nitrile groups.     

Two-photon induced optical-power limiting and upconverted superradiance properties of a new organic dye HEASPI

A new organic dye trans-4-[p-(N-ethyl-N-hydroxyethylamino)styryl]-N-methylpyridinium iodide (abbreviated as HEASPI hereafter) with large two-photon absorption (TPA) cross section and excellent upconverted superradiance properties was synthesized in our group recently. The TPA cross section was measured to be σ₂′=7.0×10⁻⁴⁸ cm⁴ s/photon by using an open aperture Z-scan system. Linear absorption, single-photon induced fluorescence, two-photon induced fluorescence and two-photon pumped (TPP) upconverted superradiance properties were systematically studied. The highest net upconversion efficiency from the absorbed pump energy to the output upconverted superradiance energy is as high as 19.6% at the pump energy of 2.07 mJ from a mode-locked Nd : YAG picosecond laser. The dye solution also shows a clear optical power limiting effect.     

New method for detection of exciton Bose condensation using stimulated two-photon emission

An investigation is reported of stimulated two-photon emission by Bose-condensed excitons accompanied by a coherent two-exciton recombination, i.e., by simultaneous recombination of two excitons with opposite momenta leaving unchanged the occupation numbers of exciton states with momenta p≠0. Raman light scattering (RLS) accompanied by a similar two-exciton recombination (or production of two excitons) is also analyzed. The processes under consideration can occur only if a system contains Bose condensate, so their detection can be used as a new method to reveal Bose condensation of excitons. The recoil momentum, which corresponds to a change in the momentum of the electromagnetic field in the processes, is transferred to phonons or impurities. If the recoil momentum is transmitted to optical phonons with frequency ω ₀ ^s , whose occupation numbers are negligible, and the incident light frequency satisfies ω<2Ω, where Ω_=Ω−ω ₀ ^s is the difference frequency and Ω is the light frequency corresponding to the recombination of an exciton with zero momentum, stimulated two-photon emission and RLS with coherent two-exciton recombination give rise to a line at 2Ω_ −ω and an anti-Stokes component at ω+2Ω_, respectively. For ω2Ω_ the RLS spectrum contains Stokes and anti-Stokes components at frequencies ω±2Ω_, whereas stimulated two-photon emission is impossible. Formulas for the cross sections at finite temperatures are obtained for the processes under consideration. Our estimates indicate that a spectral line at 2Ω_−ω, corresponding to the stimulated two-photon emission accompanied by coherent optical phonon-assisted two-exciton recombination can be experimentally detected in Cu₂O. Zh. éksp. Teor. Fiz. 115, 1353–1376 (April 1999)     

Fluorescence of Styryl Dyes-DNA Complexes Induced by Single- and Two-Photon Excitation

The series of novel monomer and homodimer styryl dyes based on (p-dimethylaminostyryl) benzothiazolium residues were synthesized and studied as possible fluorescent probes for nucleic acids detection. Spectral-luminescent and spectral-photometric properties of obtained dyes in the unbound state and in DNA presence were studied. Fluorescence emission induced by two-photon excitation of dye-DNA complexes in aqueous buffer solution was registered. Two-photon absorption cross section values of the studied dyes in DNA presence were evaluated.     

Optical nonlinearities in hyperbranched polyyne studied by?two-photon excited fluorescence and third-harmonic generation spectroscopy

The nonlinear optical properties of a hyperbranched polyyne (hb-Polyyne) have been measured at infrared wavelengths by using femtosecond and nanosecond pulsed excitation. This hyperbranched polyyne exhibited strong and intrinsic (simultaneous) two-photon absorption and upconverted blue fluorescent emission under femtosecond excitation around 800 nm. The hb-Polyyne in chloroform solution is characterized by a large two-photon absorption cross section of 9068 GM (1GM=10⁻⁵⁰ cm⁴ s) and a fluorescence quantum yield of 0.57. On the other hand, by third-harmonic generation (THG) spectroscopy with nanosecond excitation, the measured third-order nonlinear susceptibility χ ⁽³⁾ for solid films of hb-Polyyne ranged from 2.4×10⁻¹¹ to 6.1×10⁻¹¹ esu in the spectral range of 1100–1600 nm, with results comparable to the values exhibited by the well-known conjugated polymer MEH:PPV, but with a much better transparency for visible wavelengths.     

Efficient two-photon absorption of CdSe-CdS/ZnS core-multishell quantum dots under the excitation of near-infrared femtosecond pulsed laser

We report that two-photon absorption (TPA) properties of semiconductor CdSe-core CdS/ZnS-multishell quantum dots (QDs) in toluene under excitation of femtosecond laser at 800 nm. The results show efficient TPA process and large TPA cross section of three types of size QDs, which is 1900, 5710, and 16060 GM (1 GM = 10⁻⁵⁰ cm⁴ s photon⁻¹), respectively. TPA cross section dramatically increases with increased core size, showing a strong size-dependence effect. Furthermore, two-photon excitation (TPE) fluorescence intensity not only depends on TPA capacity, but also relies on improved quantum yield resulting from passivation of QD surface by different coated monolayers (MLs). These facts in combination with the narrow fluorescence bandwidth make these QDs as promising probes for multicolor two-photon microscopy.     

Fluorescence upconversion properties of a class of improved pyridinium dyes induced by two-photon absorption

We report the fluorescence upconversion properties of a class of improved pyridinium toluene-p-sulfonates having donor–π–acceptor (D–π–A) structure under two-photon excitation at 1064 nm. The experimental results show that both the two-photon excited (TPE) fluorescence lifetime and the two-photon pumped (TPP) energy upconversion efficiency were increased with the enhancement of electron-donating capability of the donor in the molecule. It is also indicated that an overlong alkyl group tends to result in a weakened molecular conjugation, leading to a decreased two-photon absorption (TPA) cross section. By choosing the donor, we can obtain a longest fluorescence lifetime of 837 ps, a highest energy upconversion efficiency of 6.1%, and a maximum TPA cross-section of 8.74×10⁻⁴⁸ cm⁴ s/photon in these dyes.     

Investigation of cross sections for the formation and destruction of negative boron ions

The electron loss and electron capture cross sections σ _i,i+m and σ _i,i−m for boron ions and atoms traveling at the velocities V=1.19 and 1.83 a.u. in H₂, He, N₂, Ne, Ar, and Xe are measured. The known experimental data on these cross sections at velocities near the cross-section maximum are analyzed. It is found that the electron loss cross sections can be described by a formula which was previously derived in the free-collision approximation and takes into account features of both the ions and the ambient atoms. As the nuclear charge Z _t of the ambient atoms increases, the cross sections vary nonmonotonically, increasing on average as Zt _t ^1/2 . A formula based on the model of independent electrons is proposed for electron capture by ions with small values of the charge i. It describes the dependence of the electron capture cross section σ _i,i−1 on the mean binding energy of an electron in an ion with the charge i−1. The total electron capture cross section σ _i,i−1 is proportional to the number of vacancies in the unfilled electron shell nearest the nucleus. The cross sections 0σ _i,i−1 exhibit substantially nonmonotonic variation with Z _t, increasing on average as Z _t ^1/3 . Zh. éksp. Teor. Fiz. 116, 1539–1550 (November 1999)     

中位取代蒽类染料的荧光及化学发光性质

本文以蒽为母体 ,中位取代合成了 6种荧光染料 [9,10 -二苯基蒽 ( DPA) ,9,10 -二苯乙炔基蒽( BPEA) ,1-氯 - DPA,1-氯 - BPEA,1-甲氧基 - DPA,1-甲氧基 - BPEA]。考察了这些荧光染料在过氧草酸酯化学发光体系中的发光行为 ,并讨论了它们的结构与其化学发光波长及强度的关系     

Properties of two-photon absorption-induced cavity lasing of an organic dye HEASPI pumped by picosecond infrared laser beam

The first operation of cavity lasing of a two-photon absorption (TPA) organic dye, trans-4-[p-(N-ethyl-N-hydroxyethylamino) styryl]-N-methylpyridinium iodide (HEASPI), by using picosecond infrared laser as pump source is reported in this paper. Temporal profile of cavity lasing shows obvious oscillations, and magnification of the feedback light can be obtained. By using the difference of re-absorption coefficient at different conditions, we explained the blue shift for cavity lasing and superradiance compared with TPA-induced fluorescence. The lifetime of TPA-induced fluorescence is measured to be 134 ps.     

Two-photon—induced fluorescence and electronic structure of substituted dicyanomethylene pyrans in solutions under femtosecond excitation

The method of two-quantum etalon is used to determine the two-photon absorption cross sections of eight dicyanomethylene (DCM) pyran dyes (DCM derivatives). Measurements of two-photon absorption of femtosecond Ti: sapphire-laser (λ = 800 nm, τ = 100 fs, and f = 89 MHz) radiation have been carried out. The nature of nonlinear excitation has been confirmed by the dependence of the fluorescence intensity on the excitation radiation intensity, which is close to a square-law one. Based on the measured two-photon absorption cross sections, the sizes of delocalized π-electronic clouds of DCM dye molecules with different substitutes are estimated in solvents with different polarity parameters. It is demonstrated that an increase in the polarity parameter of the solvent causes the two-photon absorption cross sections and sizes of delocalized π-electronic clouds of DCM, DCM-doa, DCM-17, DCM-5M, and DCM-11 dyes to increase. It is demonstrated that the size of the delocalized π-electronic cloud and the quantum fluorescence yield of the DCM-ul dye decrease with increasing polarity of the solvent despite the growth of the two-photon absorption cross section. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 69–73, November, 2005.     

Resonant two-photon absorption in a tetragonal CdP2

Kinetic, spectral, intensity, angular, and polarization of resonant two-photon absorption (TPA) in β-CdP₂ has been investigated. Resonant TPA was observed for which the total energy of the two photons was 2.60 eV. It is shown that resonant TPA takes place via a real intermediate level d ₃ in the band gap at the depth E _c-0.86 eV. The electron transverse relaxation time for resonant TPA, the cross section for absorption of laser photons in d ₃→C transitions, the equilibrium population of d ₃ centers in a doped n-type sample, and the resonant TPA constant were determined as 4.3×10⁻¹⁴ s, 1.25×10⁻¹⁷ cm², 0.95, and 0.028 cm/MW, respectively. Fiz. Tverd. Tela (St. Petersburg) 40, 1252–1256 (July 1998)     

Two-Photon Absorption in Nanoheterostructures with <Emphasis Type="Italic">D</Emphasis><Superscript>(−)</Superscript>-Centers

A two-photon impurity absorption coefficient of the “quantum dot — D⁽⁻⁾-center” complexes synthesized in a transparent dielectric matrix is calculated within the model of zero-radius potential. The evolution of spectral dependence of the absorption coefficient of the nanoheterostructure based on semiconductor CdS _x Se _1−x glasses is studied versus the average quantum-dot radius. It is shown that the contribution of the two-photon impurity absorption to the exited two-photon luminescence is fairly significant at a reasonable quantum-dot concentration. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 46–50, July, 2005.     

Synthesis and two-photon optical characterization of D-π-D type Schiff bases

The title compounds, several Schiff bases with D-π-D type have been successfully synthesized from reaction of 4-(N-dialkylamino) benzaldehyde and hydrazine or p-phenylenediamine in ethanol. These compounds were characterized by IR, ¹H NMR, elemental analysis and electronspray mass spectrometry. One-photon fluorescence and two-photon fluorescence properties have been investigated. The two-photon absorption (TPA) cross section (σ) of these compounds was obtained by using the open-aperture Z-scan technique. Based on theoretical calculations and factual test, the influence that a series of substituted groups and the conjugated frame imposed on TPA cross section were systematically discussed.     

Entangling Mesoscopic Squeezed Vacuum States and Fock States in Dissipative Cavity QED System

A scheme is proposed for generating the mesoscopic entanglement between the mesoscopic squeezed vacuum states and Fock states {|0〉,|2〉} by considering both the two-photon interaction of N two-level atoms in cavities with high quality factor assisted by a strong driving field. Moreover, we derive the dissipative interaction models for two-photon interaction. The corresponding analytical expressions of the fidelities can be given. Our scheme can be realized in the current techniques on the cavity QED.     

Quasi-long-range order in the random anisotropy Heisenberg model

The random field and random anisotropy N-vector models are studied with the functional renormalization group in 4−ε dimensions. The random anisotropy Heisenberg (N=3) model has a phase with an infinite correlation length at low temperatures and weak disorder. The correlation function of the magnetization obeys a power law 〈m(r ₁)m(r ₂)〉∼|r ₁−r ₂|^{− 0.62ε}. The magnetic susceptibility diverges at low fields as χ∼H ^−1+0.15ε. In the random field N-vector model the correlation length is finite at arbitrarily weak disorder for any N>3. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 130–135 (25 July 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

EPR of trivalent iron ions in a LiCaAlF6 crystal

The orientational dependences of the EPR spectra of Fe³⁺-doped LiCaAlF₆ single crystals (space group P31c, Z=2), grown at the Laboratory of Magnetic Radio Spectroscopy at Kazan’ State University, have been investigated in detail. The spectrum is described by a trigonal spin Hamiltonian with the following parameters: B ₂₀=40.072×10⁻⁴ cm⁻¹, B ₄₀=−5.799×10⁻⁴ cm⁻¹, B ₄₃=−4.281×10⁻⁴ cm⁻¹, A _s=24.33±1, A _p=6.13±1, g _∥=g _⊥=2.00217±0.0003. A theoretical calculation of the hyperfine structure parameters shows that they are described quite well when allowance is made for the overlapping of the wave functions of the paramagnetic center and the ligands (F⁻). Fiz. Tverd. Tela (St. Petersburg) 39, 488–490 (March 1997)     

Adaptive synthesis of optical pattern for photonic crystal lithography

The two-photon absorption spectrum and cross-section (δ) for ruby (Cr³⁺:sapphire) have been measured over the 0.8–1.2 μm wavelength range at 25°C. Absolute values of δ were obtained by comparing the fluorescence yield for two-photon excitation with that for single-photon excitation of the same ionic transition under identical illumination conditions. The maximum values of δ are 4.6×10⁻³ GM for o-polarisation and 5.9×10⁻³ GM for e-polarisation at 840 nm. The relevance of these measurements to distributed optical fibre sensing is briefly discussed.     

Discovery of a narrow resonance state of the system K S K S at mass 1520 MeV

Data are presented which indicate the existence of a previously unknown narrow resonance near mass 1520 MeV, discovered while analyzing the system K _S K _S . The data were obtained at ITEP using the 6-m magnetic spectrometer in a beam of 40-GeV negative particles. The resonance is observed in π⁻ p and K ⁻ p interactions with a total statistical confidence of not less than 5 standard deviations. The width of this state is comparable to the mass resolution of the spectrometer (∼5 MeV). The mass is 1521.5±2.5 MeV. Estimates of the product σ·BR (K _S K _S ) give ∼5.0 nb in π⁻ p interactions and ∼250 nb in K ⁻ p interactions. From the fact that the production cross section of this resonance in the K ⁻ beam is approximately 50 times greater than the production cross section in the π⁻ beam, it can be concluded that this new state belongs to a system of mesons with hidden strangeness. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 4, 242–246 (25 August 1999)