Two-photon excitation and ionization of the 2s shell of the argon atom

The absolute values and the form of the cross section for two-photon one-electron excitation and ionization of the deep 2s shell of the Ar atom are calculated taking into account the many-body effects of relaxation of the atomic core in the fields of arising virtual vacancies and the decay of vacancies via the Auger and (or) radiative channels. The one-electron wave functions are calculated in the nonrelativistic approximation. The appearance of the Cooper minimum in the two-photon absorption cross section is established. The calculations are carried out for the linear and circular polarizations of photons of an incident laser beam.     

原子双光子激发截面的计算

在不可约张量法基础上,利用二次量子化方法计算了原子的双光子激发截面.作为一个实例,计算了Hg原子的双光子激发截面.理论结果与实验结果在数量级上有较好的符合.     

溶剂对N-{4-[(反式)-2-(4-硝基苯基)乙烯基]苯基}-N,N-二苯氨基分子双光子吸收特性的影响

在从头计算的基础上,利用两态模型对溶剂对N-{4-[(反式)-2-(4-硝基苯基)乙烯基]苯基}-N,N-二苯氨基分子双光子吸收特性的影响进行了理论研究.计算结果表明,溶剂对该分子的双光子吸收截面影响较大,双光子吸收截面随着溶剂极性的增加而增加.     

4,4''-二甲氨基二苯乙烯双光子吸收理论研究--溶剂效应

对最近实验室合成的分子材料 4 ,4 ' 二甲氨基二苯乙烯的双光子吸收特性在从头计算的基础上进行了理论研究。理论模型是建立在密度泛函理论的基础上的。利用含时的密度泛函理论来计算分子的非线性光学性质 ,而溶剂效应则通过自洽响应场方法的极化连续模型来模拟。计算结果表明 ,三态模型可以很好地给出该分子在低激发态范围内的双光子吸收截面。随着溶剂极性的增加 ,单光子波长红移 ,双光子吸收截面增加。双光子吸收截面的大小和实验给出的结果符合得较好。     

Effect of electron and γ polarization on two-photon bremsstrahlung of electrons in a nuclear field

The cross section for two-photon bremsstrahlung is integrated over the electron scattering angle and the (common) emission angle of the bremsstrahlung photons. Equations are found for the energetic, angular, and polarization distributions of the cross section. The cross section for two-photon bremsstrahlung for the case in which the momenta of the bremsstrahlung photons are parallel can be larger than the corresponding Bethe-Heitler cross section. The probabilities for certain polarization states of the electrons are also analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 13–18, July, 1972.     

Two-photon excitation/ionization of deep shells of multiply charged atomic ions

Absolute values and the shape of cross sections for two-photon one-electron excitation/ionization of the 1s shell of Ne⁶⁺ and Ne⁸⁺ ions, taking into account the relaxation of the atomic core in the field of resulting vacancies, are calculated. The many-particle stabilization of a deep vacancy in moving from a neutral atom to multiply charged ions is taken into account. The calculations are made for linear and circular polarizations of the incident laser beam. The results of the calculations are predictive.     

Hg原子双光子激发截面的理论计算

以Hg原子为例,讨论了在Hartree-Slater自洽场近似的基础上,采用有限项近似和求解非齐次薛定谔方程相结合的方法,计算了双光子激发截面,该计算程序可以用于计算任意原子的双光子激发截面。 关键词：     

Solvent effects on optical properties of a newly synthesized two-photon polymerization initiator： BPYPA

Time-dependent hybrid density functional theory in combination with polarized continuum model is applied to study the solvent effects on the geometrical and electronic structures as well as one- and two-photon absorption processes, of a newly synthesized asymmetrical charge-transfer organic molecule bis-（4-bromo-phenyl）-[4-（2-pyridin-4-yl-vinyl）phenyl]-amine （BPYPA）. There exist two charge-transfer states for the compound in visible region. The two-photon absorption cross section calculated by a three-state model and solvatochromic shift of the charge-transfer states are found to be solvent-dependent, where a nonmonotonic behaviour with respect to the polarity of the solvents is observed. The numerical results show that the organic molecule exhibits a rather large two-photon absorption cross section as compared with the compound 4-trans-[p-（N, N-Di-n-butylamino）-p-stilbenyl vinyl] pyridine （DBASVP） reported previously, and is predicted to be a good two-photon polymerization initiator. The hydrogen-bond effect is analysed. The computational results are in good agreement with the measurements.     

Two-Photon Detachment Cross Section of the Positronium Negative Ion

The two-photon detachment cross section of positronium negative ion is calculated within the lowest-order perturbation theory for the final-state energies below the Ps(n = 2) threshold. A coupled-channel method with positronium orbital expansion is used to prepare the wavefunctions. The resonance structure below the threshold is clearly seen.     

Fine structure continuum cross section ratios in the two-photon ionization of rubidium using elliptically polarized light

Using fully relativistic perturbation theory we report fine structure continuum cross section ratios for the two-photon ionization of rubidium under elliptically polarized light. The choice of light polarization and wavelength matches the recent complete experiments on rubidium reported by Wang and Elliott [Phys. Rev. Lett. 84, 3795 (2000)]. The sigma(d5/2)/sigma(d3/2) cross section ratios calculated are consistent with results expected if relativistic fine structure effects are small, and are very much at odds with the recent experimental findings.     

Production and two-photon decay of the MSSM scalar Higgs bosons at the LHC

We consider the production and two-photon decay of theCP-even Higgs bosons (h ⁰ andH ⁰) of the Minimal Supersymmetric Standard Model (MSSM) at the Large Hadron Collider. We study in detail the dependence of the cross section on various parameters of the MSSM, especially the dependence on the mixing effects in the squark sector due to the Higgs bilinear parameterμ and the soft supersymmetry breaking parameterA. We find that the cross section for the production of these Higgs bosons has a significant dependence on the parameters which determine the chiral mixing in the squark sector. The cross section times the two-photon branching ratio ofh ⁰ is of the order of 15–25 fb in much of the parameter space that remains after imposing the present experimental constraints. For theH ⁰ the two-photon branching ratio is only significant if theH ⁰ is light, but then the cross section times the branching ratio may exceed 200 fb. The QCD corrections due to quark loop contributions are known to increase the cross section by 50%. We find the dependence of the cross section on the gluon distribution function used to be rather insignificant.     

二苯乙烯衍生物分子双光子吸收截面：官能团对称性的影响

选取了具有不同对称性的二苯乙烯系列衍生物分子，在HF水平上，利用响应函数方法，研究了该系列分子的单光子和双光子特性. 研究结果表明，该系列分子具有较强的双光子特性. 在可见光范围内，反对称分子的最大双光子吸收态是第一激发态，而对称分子的最大双光子吸收出现在第四激发态. 相对于对称分子而言，反对称分子具有更大的双光子吸收截面. 因此，分子的对称性是否比不对称性更有利于增大分子的双光子吸收截面，还与分子的π中心部分的特性有关. 还给出了电荷转移态的电荷迁移过程. 关键词： 双光子吸收 响应函数方法 非线性光学     

Laser photolysis as applied to the determination of the two-photon absorption cross section of <Emphasis Type="Italic">trans</Emphasis>-stilbene

The two-photon absorption (TPA) cross section of an ethanol solution of trans-stilbene exposed to radiation of the second harmonic of a Nd:YAG laser (532 nm) of nanosecond duration has been determined using the method based on the measurement of the photodecomposition of trans-stilbene molecules, characterized by a low photostability. The measured TPA cross section of trans-stilbene in ethanol amounts to 25 ± 5 GM, and the photodecomposition quantum yield determined upon excitation by radiation of the fourth harmonic of the Nd:YAG laser (266 nm) is found to be γ = 0.10 ± 0.01. The obtained value of the TPA cross section has been compared with the experimental and theoretical data of other authors. The method of photodecomposition can be successfully used for the experimental determination of the TPA cross section of compounds unstable under the photoexcitation such as photochromic molecules, biological objects, and radical photoinitiators.     

Effects of radial relaxation and intershell correlations during resonance inelastic photon scattering by an atom

The absolute value and shape of the double differential cross section of the resonance inelastic scattering of a linearly polarized photon in the ionization threshold energy range of the subvalence s shell of the free neon or argon atom are calculated in the nonrelativistic approximation for one-electron wavefunctions and in the dipole approximation for the anomalously dispersive scattering probability amplitude. The effects of radial relaxation, intershell correlations, bremsstrahlung, spin-orbit splitting, and a finite decay width of s vacancies are taken into account. The effects of radial relaxation and intershell correlations substantially affect the near-threshold scattering intensity: they decrease the contribution of the leading Compton anomalously dispersive component of the total cross section calculated in the one-electron approximation by several times. The calculation results have a predictive character.     

Charm production in two-photon collisions: Calculation of the leading nonperturbative contribution in QCD

The leading nonperturbative contribution to the cross section of charm production in two-photon collisions is calculated in QCD. Operator expansion is used and the c-quark interaction with vacuum gluon condensate is taken into account. As a result, the moments of the charm contribution to the photon structure function are obtained. The moments with sufficiently high numbers turn out to be sensitive to the gluon condensate.     

反-4,4''-双(N,N-二丁胺基)二苯乙烯分子双光子吸收性质研究

对于实验室合成的反-4,4'-双(N,N-二丁胺基)二苯乙烯分子,实验测量了该分子的单光子和双光子荧光谱,然后从理论上研究了其单光子和双光子吸收特性.研究结果表明,在低能量范围内,分子的单光子吸收主要发生在分子的第一激发态,而分子的双光子吸收主要发生在分子的第二和第四激发态上.该分子在相应系列衍生物中具有最大的双光子吸收截面.分子的相关能对分子的激发态能量影响较大.我们给出了分子基态与电荷转移态的电荷转移过程,并从理论上定性解释了双光子聚合反应的聚合机理.     

Two-photon-exchange effects in the electroexcitation of the delta resonance

We examine the two-photon exchange contribution to the eN --> edelta(1232) --> epiN process with the aim of a precision study of the ratios of electric quadrupole (E2) and Coulomb quadrupole (C2) to the magnetic dipole (M1) gamma*Ndelta transitions. We relate the two-photon exchange amplitude to the N --> delta generalized parton distributions and obtain a quantitative estimate of the two-photon effects. The two-photon exchange corrections to the C2/M1 ratio depend strongly on whether this quantity is obtained from an interference cross section or from the Rosenbluth-type cross sections, in similarity with the elastic, eN --> eN, process.     

Theoretical studies on the one- and two-photon absorption properties of azulenylporphyrins and azulene-fused porphyrins

The electronic structures, one-photon absorption (OPA) and two-photon absorption (TPA) properties of the azulenylporphyrins and azulene-fused porphyrins have been comparatively studied by using DFT/B3LYP/6-31G(d) and the ZINDO/SDCI method. With the number of azulenyl groups increasing, the OPA wavelengths of all molecules are red-shifted in 400--600~nm and the two-photon absorption cross section is gradually enlarged. The azulene-fused structures facilitate an expanding conjugated area and increasing TPA cross section. The origin of TPA properties of studied compounds is studied with a two-level model. In summary, the azulene-fused porphyrins exhibit strong two-photon absorption.     

Two-photon absorption and laser photolysis of trans-stilbene substitutes

The measured the two-photon absorption (TPA) cross sections of ethanol solution of trans-stilbene and its two substitutes excited by nanosecond radiation of the 2nd harmonic of a Nd:YAG laser (532 nm) are presented. To determine the TPA cross section, a method based on measurements of photochemical decomposition of molecules of the examined compounds having low photostability is suggested. The measured value of the TPA cross section of trans-stilbene in ethanol is found to be 25 GM, and the TPA cross sections of the trans-stilbene substitutes are found to be 60 and 70 GM. The TPA cross section of trans-stilbene substitutes obtained in the present paper is compared with the experimental and theoretical data obtained by other authors. The results of investigations demonstrate that the photochemical decomposition method can be successfully used to determine experimentally the two-photon absorption cross section of the compounds unstable under photoexcitation, including photochromatic molecules, biological objects, and radical photoinitiators.