Spontaneous relativistic two-photon decay rate mathematical expression in helium-like systems

Using a laser-induced fluorescence method a detailed analysis of profiles of the ¹¹⁴Cd 326.1 nm line perturbed by argon was performed which revealed deviations from the ordinary Voigt profile. These deviations are shown to be consistent with fits of experimental profiles to an asymmetric Voigt profile. Coefficients of the pressure broadening, shift and collision-time asymmetry are determined and compared with those calculated in the adiabatic approximation for different interaction potentials. Received 19 July 2000     

Orbital electron capture decay of hydrogen- and helium-like Pm ions

The β⁺${\beta }^{+}$ and orbital electron-capture decays of stored hydrogen- and helium-like ¹⁴²Pm ions have been measured. So far, such measurements have been performed with only one nucleus, namely ¹⁴⁰Pr. The electron-capture decay constant of hydrogen-like ¹⁴²Pm⁶⁰⁺ ions is about 50% larger than that of helium-like ¹⁴²Pm⁵⁹⁺ ions, which is in excellent agreement with the previous measurements in ¹⁴⁰Pr ions and with new theoretical predictions.     

Plasmonic-enhanced two-photon fluorescence with single gold nanoshell

Single gold nanoshell with mutilpolar plasmon resonances is proposed to enhance two-photon fluorescence efficiently.The single emitter single nanoshell configuration is studied systematically by employing the finite-difference time-domain method.The emitter located inside or outside the nanoshell at various positions leads to a significantly different enhancement effect.The fluorescent emitter placed outside the nanoshell can achieve large fluorescence intensity given that both the position and orientation of the emission dipole are optimally controlled.In contrast,for the case of the emitter placed inside the nanoshell,it can experience substantial two-photon fluorescence enhancement without strict requirements upon the position and dipole orientations.Metallic nanoshell encapsulating many fluorescent emitters should be a promising nanocomposite configuration for bright two-photon fluorescence label.The results provide a comprehensive understanding about the plasmonic-enhanced two-photon fluorescence behaviors,and the nanocomposite configuration has great potential for optical detecting,imaging and sensing in biological applications.     

Photon polarization in the two-photon decay of heavy hydrogen-like ions

We have applied the density matrix and second-order perturbation theory in order to re-analyze the two-photon decay of hydrogen-like ions for the polarization of emitted light. Special attention is paid to the linear polarization of one of the photons, while the spin state of the second photon is supposed to be unobserved. For such an “angle-polarization” correlation of the two photons we investigate the contributions that arise from non electric-dipole terms in the expansion of the electron-photon interaction. Detailed calculations are performed for the 2s_1/2 →1s_1/2 and 3d_5/2 →1s_1/2 transitions in neutral hydrogen as well as in hydrogen-like uranium.     

Large prolongation of free-exciton photoluminescence decay in diamond by two-photon excitation

We report on time-resolved photoluminescence of a free-exciton in IIa chemical vapor deposition diamond crystal. Large difference between decay times for one- and two-photon excitation processes was observed. The longest room-temperature exciton photoluminescence lifetime τ(FE)=220 ns was obtained under two-photon excitation with a photon energy of 4.7 eV. The role of diffusion and surface recombination velocity in exciton photoluminescence dynamics was studied using a new optical method based on two-photon excited time-resolved photoluminescence. The measured room-temperature value of diffusion coefficient in diamond was D=40 cm(2)/s.     

Observation of the two-photon decay of a light penetrating particle

Coincident two-photon events, emerging from a 2 m long decay region, and pointing back to the SIN 590 MeV proton beam dump were detected in a thin-foil optical spark chamber. There was a significant excess of photons at small angles (<7°): 19 were observed, whereas (2.0 ± 0.5) were measured with cosmic rays, and additional (2.5 ± 1.0) were accelerator background. The visible γ-ray energies were estimated by multiple scattering to be 〉E_γ1〈 = (83 ± 20) MeV, 〉E_γ2〈 = (84 ± 15) MeV. The invariant 2γ mass is < 1 MeV. The 2γ event rate did not change significantly, when a 20 cm thick iron wall was placed in front of the decay region, but vanished with the wall put at its end. Presumably a light boson χ⁰ comes from the beam dump, penetrates the shielding, and decays: χ⁰ → 2_γ The measured rate of (14.5 ± 5.0) events in 129 Coulomb fixes a combination of production cross section and life-time. If the new boson χ⁰ was the axion, one can solve for the Higgs parameter X = 3.0 ± 0.3, and infer τ_a ≈ 7 ms, and m_a = (250 ± 25) keV.     

The spectra of helium-like ions in laser-produced plasmas

We calculate intensities of lines arising from the n = 2 and n = 3 levels of highly-charged, helium-like ions in very dense plasmas. We determine the importance of recombination and cascading, and of radiation trapping, on certain line-intensity ratios, and we illustrate the relevance of these calculations to laser-plasma diagnostics. Finally, we outline the pitfalls inherent, at very high densities, in some other techniques commonly used to interpret plasma spectra.     

Hole states in helium-like ions

An analysis is made of the poles of the single-particle Green's function of helium-like ions in which electron correlation is taken into account on the basis of the model of singly filled orbitals. The energy of Hartree-Fock pole calculated through the use of the hydrogen-like wave functions for the orbitals turns out to be approximately equal to the exact value. The second pole, which corresponds to a different hole state, has a residue which vanishes as z increases and must be considered fortuitous.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 90–93, April, 1971.     

Polarization correlation in the two-photon decay of atomic hydrogen: nonlocality versus entanglement

From the work by Perrie et al. [Phys. Rev. Lett. 54, 1790 (1985)], photon pairs from the 2s _1/2 → 1s _1/2 (two-photon) decay of atomic hydrogen are known to be quantum mechanically correlated. In these experiments, the polarization states of the photons emitted in back-to-back geometry were shown to violate the Bell inequality as a qualitative sign of nonlocality and entanglement. In the present contribution, we analyze how these nonlocal quantum correlations, as given by the violation of the Bell inequality, differ from the concurrence as a true entanglement measure. Results are shown for both quantifiers in dependence of the decay geometry and the initial polarization of the atoms for the 2s _1/2 → 1s _1/2 and 3d _5/2 → 1s _1/2 two-photon decay of atomic hydrogen. These results display the difference between nonlocality and entanglement and, hence, may stimulate further experiments on nonlocal quantum correlations in atomic systems.     

Local second-harmonic generation enhancement on gold nanostructures probed by two-photon microscopy

The localization of surface second-harmonic generation (S-SHG) enhancements from granular gold structures that exhibit local plasmon resonance was investigated. A two-photon microscopy technique was used to perform high spatial resolution S-SHG imaging. The magnitude and the spatial density of S-SHG enhancement confined in submicroscopic regions are strongly dependent on the morphology of the gold's surface. Polarization measurements of local S-SHG responses reveal the local field anisotropy in enhancement regions and furthermore prove the incoherent and strongly depolarized nature of the emission, which is attributed to ultrafast fluctuations of the enhancement location in the focal volume.     

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.     

Application of B-splines finite basis sets to relativistic two-photon decay rates of level in hydrogenic ions

A theoretical study of the one- and two-photon spontaneous emission rates from the 2 s1/2 state of one-electron ions is presented. High-precision values of the relativistic emission rates for ions with nuclear charge Z up to 100 are obtained through the use of finite basis sets for the Dirac equation constructed from B-splines. Furthermore, we analyze the influence of the inclusion of quantum electrodynamics corrections in the initial and final state energies. Received: 6 January 1998 / Accepted: 31 March 1998     

Wavefunctions of helium-like systems in limiting regions

We find an approximate analytic form for the solution ψ(r ₁, r ₂, r ₁₂) of the Schrödinger equation for a system of two electrons bound to a nucleus in the spatial regions r ₁ = r ₂ = 0 and r ₁₂ = 0, which are of great importance for a number of physical processes. The forms are based on the well-known behavior of ψ(r ₁, r ₂, r ₁₂) near the singular triple coalescence point. The approximate functions are compared to the locally exact ones obtained earlier by the correlation function hyperspherical harmonic (CFHH) method for the helium atom, light helium-like ions, and the negative ion of hydrogen H^?. The functions are shown to determine a natural basis for the expansion of CFHH functions in the considered spatial region. We demonstrate how these approximate functions simplify calculations of high-energy ionization processes.     

Laser induced two-photon decay in Pr3+:LaAlO3

A laser induced two-photon decay has been observed between the ³P₀ and ³F₂ levels of trivalent praseodymium in LaAlO₃. The differential transition cross section was found to be dσ/dΩ = 1.1 × 10^-27 cm².