Two-photon absorption method for the study of collisional relaxation of atoms in a perturber bath

A two-photon absorption study was performed with sodium vapour at about 300°C perturbed by noble gases at densities between 0.5 x 10¹⁹ and 6 x 10¹⁹ atoms/cm³. The collisional relaxation of the 3P_{$\text{3}\text{2}$} and 3P_{$\text{1}\text{2}$} states has been measured for several noble gases. The origin of relaxation is interpreted as the result of a reactive collision leading to an excited molecular state. The recombination rate coefficients of the three-body reaction are calculated and their values are compared to those given by Scheps and Gallagher.     

Long-wavelength excitations in a Bose gas at zero temperature

The long-wavelength excitations in a simple model of a dilute Bose gas at zero temperature are investigated from a purely microscopic viewpoint. The role of the interaction and the effects of the condensate are emphasized in a dielectric formulation, in which the response functions are expressed in terms of regular functions that do not involve an isolated single-interaction line nor an isolated single-particle line. Local number conservation is incorporated into the formulation by the generalized Ward identities, which are used to express the regular functions involving the density in terms of regular functions involving the longitudinal current. A perturbation expansion is then developed for the regular functions, producing to a given order in the perturbation expansion an elementary excitation spectrum without a gap and simultaneously response functions that obey local number conservation and related sum rules.Explicit results to the first order beyond the Bogoliubov approximation in a simple one-parameter model are obtained for the elementary excitation spectrum ω_k, the dynamic structure function $\text{S}$(k, ω), the associated structure function $\text{S}$_m(k), and the one-particle spectral function $\text{A}$(k, ω), as functions of the wavevector k and frequency ω. These results display the sharing of the gapless spectrum ω_k by the various response functions and are used to confirm that the sum rules of interest are satisfied. It is shown that ω_k and some of the $\text{S}$_m(k) are not analytic functions of k in the long wavelength limit. The dynamic structure function $\text{S}$(k, ω) can be conveniently separated into three parts: a one-phonon term which exhausts the f sum rule, a backflow term, and a background term. The backflow contribution to the static structure function $\text{S}$₀(k) leads to the breakdown of the one-phonon Feynman relation at order k³. Both $\text{S}$(k, ω) and $\text{A}$(k, ω) display broad backgrounds because of two-phonon excitations. Simple arguments are given to indicate that some of the qualitative features found for various physical quantities in the first-order model calculation might also be found in superfluid helium.     

Sodium resonances in fluorescence from wide-range laser scan in H2-O2-Ar flame

Several resonances and underlying continua were observed in the excitation profiles of sodium atoms in an H₂-O₂-Ar flame, irradiated by the focused beam of a tunable, pulsed dye layer. These profiles are obtained by tuning the laser through the spectral range of Rhodamine 6G and detecting the ensuing fluorescence signals from the 3D-3P and 4D-3P transitions. We observed resonances corresponding to the 3S_{$\text{1}\text{2}$}-3P_{$\text{1}\text{2}$}, 3S_{$\text{1}\text{2}$}-3P_{$\text{3}\text{2}$}, 3P_{$\text{1}\text{2}$}-5S_{$\text{1}\text{2}$}, 3P_{$\text{3}\text{2}$}-5S_{$\text{1}\text{2}$} one-photon transitions and resonances corresponding to the 3S_{$\text{1}\text{2}$}-5S_{$\text{1}\text{2}$}, 3S_{$\text{1}\text{2}$}-4D_{$\text{3}\text{2}$}, _{$\text{5}\text{2}$} two-photon transitions. The observed resonances result from different sequences of radiative and collisional excitation. The presence of the continua is explained by consecutive absorption of laser photons in the collisionally broadened wings of absorption lines. The spatial inhomogeneity of the laser beam and hence of the saturation causes submerging of some resonances into continua.     

KMS condition in a Schrödinger picture of the dynamics

Given the C¹-algebra $\text{A}$ of observables, the KMS condition is formulated in terms of the time evolution α¹_t of a set $\text{S}$₀ ? $\text{S}$($\text{A}$) of “physical” states subject to certain natural conditions. α¹_t need not be defined by an automorphism group of $\text{A}$. It is shown that, for a KMS state ω, α¹_t induces a 1-automorphism α^ω_t of the von Neumann algebra π_ω($\text{A}$)″ generated by the representation π_ω belonging to ω.     

On the asymptotic behaviour of the mass operator near the Fermi energy

By taking due account of momentum conservation, it is shown that, when ω is near the Fermi energy ω_F, the imaginary part of the mass operator $\text{M(}\text{k}\text{, ω)}$ for an infinite Fermi system behaves like (ω ? ω_F)^p(k) where the exponent p(k) ? 2 depends on the interval in which $\text{|}\text{k}\text{|}$ is lying. In particular, the commonly asserted quadratic behaviour (ω ? ω_F² is shown to be true only for $\text{|}\text{k}\text{| ? 3k}{}_{\mathrm{<mtext>F</mtext>}}$. It is explicity assumed that the Fermi system admits a perturbative type treatment.     

Tunable diode laser measurements of the band strength and collision halfwidths of nitric oxide

The strength of the fundamental absorption band of nitric oxide at 5.3 μm and collision halfwidths of nitric oxide lines broadened by nitrogen, argon, and combustion gases were measured in absorption cell, flat flame and shock tube experiments using a tunable diode laser. Room temperature absorption measurements were made in an absorption cell filled with NO/N₂ or NO/Ar mixtures or with probe-extracted combustion gases. High temperature (to 2500 K) absorption measurements were performed for NO in N₂ and NO in Ar using a shock tube, and for NO in combustion gases using a flat flame burner.Absorption measurements were made on lines from 1860–1925 cm^?1, ($\text{Ω=}\text{1}\text{2}$ and $\text{3}\text{2}$,P($\text{5}\text{2}$-R ($\text{29}\text{2}$)) resulting in a band strength of 123±8 cm^-2 atm^?1 at 273.2 K. Collision halfwidth dependencies for each broadening species were examined as a function of rotational quantum number and temperature.     

Vibronic properties of the F+ centre in strontium oxide

The shape and moments of the F⁺ absorption band in SrO have been measured between 4.2K and 300K. Analysis of the moments gives the effective frequency of the vibrational modes interacting with the centre as $\text{h}\text{?}\text{ω = 236 ± 20 cm}{}^{-1}$, and the Huang-Rhys factors for cubic and non-cubic modes as S_C = 3 ± 1 and S_NC = 4 ± 1 respectively.     

Effect of two-photon saturation on ordinary Raman scattering

The excitation profile of ordinary Raman scattering under steady-state excitation conditions and the time-resolved emission spectrum of ordinary Raman scattering under transient excitation conditions undergo considerable changes when the excitation frequency ω approaches $\text{1}\text{2}$ ω_mn, where ω_mn is the resonance frequency of a two-photon transition from the ground state |n to an excited state |m of a molecule. The appearance of ghost peaks, dips or dispersion-like features centred at ω ? $\text{1}\text{2}$ ω_mn in the excitation profile and of coherence effects such as Rabi nutations with unusual time-dependence in the time-resolved spectrum are predicted.     

Energies of the n2S12 and n2D32,52 states of Cs

Using the technique of Doppler-free two-photon spectroscopy the energies of the n²S_{$\text{1}\text{2}$} (12 ? n ? 35) and n²D_{$\text{3}\text{2}$,$\text{5}\text{2}$} (11 ? n ? 48) states of CsI have been measured with a thermionic detector. The absorption spectrum of molecular iodine was used as a reference giving us a total estimated accuracy of about 2 × 10^-7. Taking also into account the energies of the 7–11 ²S_{$\text{1}\text{2}$} and 5 and 6 ²D_{$\text{3}\text{2}$,$\text{5}\text{2}$} states measured by other authors and using an extended Ritz-formula we found the ionization limit to be E_i = 31406.468 ± 0.006 cm^-1.     

NMR investigation of the layered transition metal phosphorus trichalcogenides and the intercalation compounds LixNiPS3

The transition metal phosphorus trichalcogenides MPX₃ are layered semiconductors which can be intercalated either chemically or electrochemically by lithium atoms. We present a NMR study of the magnetic properties of the MPX₃ compounds (M = Ni, Mn, Fe; X = S, Se) and their modification as a function of intercalation in the compounds Li_xNiPS₃ (x = 0 ? 1.29). In the concentration range x = 0.02 ? 0.5, the relative shift of the P³¹ resonance line K_iso = -0.052 % and the Neel temperature T_N = 155 K are constant and barely different from that measured in pure NiPS₃ (K_iso = -0.057 %, T_N = 165 K). For x > 0.5 a new P³¹ resonance line is observed, which grows with x at the expense of the previous one. It corresponds to non magnetic layers $\text{S - Ni}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{(P}{}_2\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{- S}$, which progressively replace the paramagnetic ones up to the limit of intercalation x = 1.29. Investigation of the lithium ions mobility through Zeeman and dipolar spin lattice relaxation times T_1～ and T_1D measurements indicates a very low self-diffusion coefficient - D = 10^-13 ? 10^-14cms^-1 -, that is four orders of magnitude smaller than those measured in Li_xTiS₂ compounds. This strongly contrasts with the good electrochemical activity of the Li_xNiPS₃ system.     

Magnetic field dependent optical dephasing in LaF3:Er3+

Optical dephasing of the 5388 Å transition between the lowest Kramers doublets of the ⁴S_{$\text{3}\text{2}$} and ⁴I_{$\text{15}\text{2}$} multiplets of Er³⁺:LaF₃ has been studied by photon echo, optical phase switching and optical free induction decay. Er³⁺?¹⁹F hyperfine interactions produce dephasing which is two orders of magnitude faster than in previously studied non-Kramers systems, but at high field changes in the spin dynamics result in microsecond dephasing. For the lower Zeeman component of ⁴S_{$\text{3}\text{2}$}, T₂ (=6μs) is independent of H₀ whereas for the upper component the dephasing is rapid and strongly field dependent. This is quantitatively accounted for by spin lattice relaxation of the upper component of ⁴S_{$\text{3}\text{2}$}. Below 20 kG concentration and temperature dependent dephasing due to electron spin diffusion is observed.     

Study of the CulCu2S system. conductivity of the solid solution Cu1+xI1−xSx(x<0.5)

A structural study of the CuICu₂S system has shown that a large solid solution ranges from pure CuI to Cu₃SI with a regular decrease of tehcell parameter ($\text{a=6.045 to 5.901}\text{A}\text{?}$); for richer Cu₂S concentrations, two-phase systems appear with the formation of a new Cu₇S₃I compound, and another solid solution exists for higher Cu₃S fractions (0.85<x<1). The ionic conductivity of the solid solution Cu_1+xI_1?xS_x (x<0.5) has been measured as a function of temperature between 54 and 307°C. The conductivity increases from 10^?7 ω^?1 cm^?1 (CuI) to 10^?3 ω^?1 cm^?1 (Cu_1.4I_0.6 S_0.4) at 25°C and then decreases until 10^?4 ω^?1 cm^?1 (Cu₃SI). In this last domain, no further phase transition occurs below the melting point and the low temperature γ phase can be considered as a stabilization of the high-conducting α phase. The variations of the conductivity are directly connected to those of the activation energy that decreases to a minimum value of 2.5 kcal mole^?1 for Cu_1.4I_0.6S_0.4.     

Possible anionic clusters and mixed valence effects in transition metal chalcogenides and oxides

The formation of anionic clusters similar to O₂^2?, S₂^2?, Se₂^2? but with higher internuclear distances can be responsible for the more specific forms of interaction required to explain the properties of UO₂₊x, and many transition metal chalcogenides such as Fe_1?xS, Ni_1?x,S etc. Resonant structures can lead to clusters of this type even in stoichiometric chalcogenides with NiAs-type structure due to the $\text{d}\text{p}$ mixing, and low energy differences between metal d- and chalcogen p-bands. The mixed valence effects involved are discussed qualitatively.     

Two-photon optically pumped laser

At high temperature, the transmission peaks of a Fabry-Perot cavity filled with rubidium show sharp structures when the frequency of the laser is close to the 5S_{$\text{1}\text{2}$} - 5D_{$\text{5}\text{2}$} two-photon transition. These structures correspond to a laser emission between 5D_{$\text{5}\text{2}$} and 5P_{$\text{3}\text{2}$}. The wavelength of this laser emission (7759 Å) is smaller than the exciting wavelength (7779 Å).     

A frequency-doubled frequency-stabilized cw ring dye laser for spectroscopy: A study of the λ = 293.3 nm transition in In1

In this letter a frequency-doubled frequency-stabilized CW ring dye laser for the wavelength region 292–305 nm is described. 500 μW U.V. power combined with a 2 MHz linewidth and a 7 GHz scanwidth has been obtained by intracavity frequency doubling in an ADA crystal. The set-up has been tested on the hyperfinestructure of the λ = 293.3 nm transition 5p²P_{$\text{3}\text{2}$} → 7s²S_{$\text{1}\text{2}$} in In1.     

Tunable XUV radiation generated by nonresonant frequency tripling in neon

Nonresonant frequency tripling of ultraviolet (UV) radiation (λ_uv = 216–223 nm, generated by sum frequency mixing of the outputs of a frequency doubled pulsed dye laser and of the Nd-YAG pump laser) generates in neon coherent light in the extreme ultraviolet (XUV). The XUV radiation is tunable in spectral regions of negative dispersion λ_xuv = 72.05- 73.58 nm and λ_xuv = 74.3–74.36 nm at the high energy side of the transitions $\text{2p-3s′[}\text{built1}\text{2}\text{, 1]}$ and $\text{2p-3s[}\text{built3}\text{2}\text{, 1]}$. At UV input powers of 0.1-0.3 MW the generated XUV power was typically P_xuv = 0.1-0.4 W (1.5–6 x 10⁸ photons/pulse). Since present UV dye laser systems provide at λ_uv pulse powers of almost 1 MW the XUV output could easily be increased by more than one order of magnitude.     

Low-energy e4 compton scattering of spin-12 targets without C,P and T invariances

We have studied the low-energy e⁴ Compton scattering on $\text{spin}\text{-}\text{1}\text{2}$ targets without assuming C, P and T invariances. It is shown that the scattering amplitude has a term ω³ ln ω (ω is the energy of incident photon in the lab frame), whose coefficient is determined entirely by the charge, mass, magnetic dipole moment, and electric dipole moment of the target. To derive the result, we calculate the second-order (in ω) terms of the e² Compton scattering amplitudes. When the electric dipole moment (whose existence violates P and T but conserves PT) is set to zero, the result reduces to that obtained before by Lin assuming C, P and T invariances.