Three-photon absorption and subsequent excited-state absorption in CdS

The nonlinear absorption of single picosecond light pulses (λ = 1.06 μm) in CdS is investigated at very high light intensities. Three-photon absorption and subsequent excited-state absorption of the generated electrons and holes explain the rapid decrease of transmission with increasing intensity. A three-photon absorption cross-section of σ⁽³⁾ = (2±0.5) × 10^-80 cm⁶ s² and an average excited state absorption cross-section of σ_ex = (7 ± 3) × 10^-18 cm² was determined.     

Excited state absorption of 1,3,3,1′,3′,3′-hexamethylindotricarbocyanine Iodide: A quantitative study by ultrafast absorption spectroscopy

A quantitative investigation of HITC dissolved in methanol has been made using the method of ultrafast absorption spectroscopy with a streak camera. Samples were excited by picosecond pulses of a mode-locked ruby laser. Analysis of time-resolved spectra yielded non-exponential decay kinetics consisting of a fast (τ variable) and a slow (τ=1.13±0.08 ns) component. The excited state absorption spectrum has its maximum at 493 nm and shoulders at 415 and 540 nm. The excited state absorption cross section was determined by simulataneous measurement of the bleaching of ground state absorption taking polarization of excitation and probe light and excited state absorption at the laser wavelength into account. A value of σ₁ (493 nm)=1.0·10^?16 cm² was found.     

Setting bounds on critical exponents with event-by-event analysis of nuclear fragmentation data

And analysis of recent ISiS data [1] is performed and a comparison with percolation-based theories is conducted. We pay particular attention to detector acceptance corrections as well as the role of sequential decays of excited pre-fragments. The corrected data are subjected to a scaling analysis. We find evidence for a continuous phase transition in these nuclear multi-fragmentation events and extract the value for the critical exponents: σ=0.5±0.1 and τ=2.35±0.05. In addition, we find T _c=8.3±0.2 MeV.     

Influence of the polarity of a medium on the photonics of a merocyanine dye with a high quadratic polarizability

The influence of the polarity of a medium on the spectral and luminescent properties of 2-[(2E,4E)-6-(1,3,3-trimethyl-2,3-dihydro-1H-2-indolyliden)-2,4-hexadienyliden]malononitrile (THDM) in solutions and polymer matrices is studied at room temperature under conditions of steady-state and pulsed laser excitation. A large bathochromic shift of the absorption spectra observed upon an increase in the polarity of a solvent is caused by a strong increase in the molecular dipole moment μ due to a transition of molecules from the ground state (μ_g = 7.6 D) to an excited Franck-Condon state (μ^FC = 33.5 D). Based on the solvatochromic data, the quadratic polarizability was calculated to be β = (3.2 ± 0.6) × 10^?28 esu, which is close to the experimentally determined value β_ex = (3.9 ± 0.2) × 10^?28 esu. A strong narrowing of the fluorescence spectra in comparison with the absorption spectra is observed upon an increase in the solvent polarity. This narrowing is explained by a decrease in the bond length alternation parameter and by weakening of vibronic interactions in the singlet excited state. The dynamic solvatofluorochromism of THDM in the picosecond range is caused by reorientations of molecules of the polar environment occurring during a time period consistent with the dielectric relaxation time of these molecules.     

Spectroscopic properties of magnesium aluminosilicate glass-ceramics doped with divalent cobalt ions

Electronic absorption and luminescence spectra and nonlinear optical properties of magnesium aluminosilicate glass-ceramics doped with divalent cobalt ions are studied in relation to their synthesis conditions. The lifetimes of the ⁴ T ₁(⁴ P) and ⁴ T ₁(⁴ F) excited levels of tetracoordinate Co²⁺ ions in these glass-ceramics are found to depend on the cobalt concentration and lie within the ranges from 25 to 40 and from 120 to 450 ns, respectively. Using the absorption saturation curves, the ground state absorption cross section for the wave-length of 1.54 μm is estimated to be σ_GSA=3.3×10^?19cm². The induced emission of the tetrahedrally coordinated Co²⁺ ion, which dominates over the absorption from the excited state in the spectral range from 640 to 690 nm (⁴ T ₁(⁴ P)→⁴ A ₂ transition), is found.     

Transverse relaxation of sodium vapour pumped by laser light

The transverse relaxation times in a sodium atomic system for different temperatures and different buffer gas pressures have been measured. Cross sections for transverse relaxation on neon atoms and in exchange collisions have been calculated. The results are σ_Na-Ne=(9.1±0.5)x10^-23 cm² and σ_ex=(1.10±0.05)x10^-14 cm².     

Half-life,g-factor and relaxation of the nuclear orientation of the isomeric 11/2− state in139Pr

By time-differential observation of the perturbed angular distribution in an external magnetic field, the g-factor of the 11/2^? isomeric state in¹³⁹Pr has been measured, g = +1.20 ± 0.09. The angular distribution also shows an attenuation with relaxation time, τ _R = 19 ± 6 ns. This relaxation is due to paramagnetic interaction of the nucleus with the 4f-electrons. Our determination of the isomeric half-life,T _1/2= 45.5 ±0.9 ns does not agree with previous measurements.     

Inelastic collision cross section of excited molecules

The (v′=6,J′=43) level in theB ¹Π _u electronic state of Na₂ has been selectively populated by excitation with the 4 880 Å line of the argon laser. Through collisions with He atoms energy is transferred to neighbouring rotational states in Na₂ and the density of these states is determined by observing fluorescence to electronic ground state. From previous measurement of the lifetime of theB ¹Π _u state and new measurements of the intensities of collision induced spectral lines as a function of He pressure, absolute collision cross sections for all rotational transitions up to ΔJ=±5 have been obtained. The total cross section for all rotational transitions observed is σ _rot ^total =65±15 Ų. Preliminary results about collision induced vibrational transitions are also presented.     

Photocaloric spectroscopy of the excited state absorption and of the fluorescence quantum efficiency in fluorescent material

A compensation photocalorimetric technique is described to determine the excited state absorption cross section σ₂ of fluorescent materials at the pump wavelength and also their fluorescence quantum efficiency Q_F. Excitation with a continuous, moderate power laser suffices. σ₂ is inferred from the pump intensity dependence of the heat conversion efficiency which is analyzed for materials without fluorescence upconversion. The σ₂ obtained is most useful as a calibration point for pump-and-probe excited state absorption measurement, for example, for an analysis of the optical pumping efficiency of laser materials. The technique is successfully tested with the well-characterized ruby (Al₂O₃:Cr³⁺) up to high excited state population densities.     

Recoil-distance measurements of the g-factor of 22Ne(21+)

Time-differential recoil-into-vacuum measurements with a plunger have been performed on the first-excited I^π = 2⁺ state of ²²Ne. The state was populated with the ⁴He(¹⁹F, p)²²Ne reaction on ⁴He-implanted foils. The measurements lead to a $\text{g-}\text{factor}\text{of}\text{¦g¦ = 0.326 ± 0.012}$ and to a mean life of τ_m = 5.2 ± 0.3 ps. The analysis also yields the population of excited two-electron ions and indicates that the population may depend on the thickness of the ¹²C contamination layer through which the ions recoil into vacuum.     

Relaxationserscheinungen im 63 P 2-Zustand des Quecksilber-Isotops199Hg bei Stößen mit Quecksilberatomen im Grundzustand

The decay ofrf resonance signals (Δm _F =± 1, ΔF=0) in the hfs-states (F=3/2, 5/2) of the 6³ P ₂-state of¹⁹⁹Hg has been observed by means of a sampling method. By comparing the relaxation times to those of the even isotopes, the cross section σ₂(F) for the destruction of an alignment in the hfs-states by collisions with ground state Hg-atoms could be measured. The following ratios were obtained: σ₂(F=3/2)/σ₂=1.04±0.06 and σ₂(F=5/2)/σ₂=0.90± 0.03. The cross section σ₂ for the even isotopes was found to be (2.620±0.265) 10^?14cm². Assuming total decoupling of nuclear spinI and electronic angular momentumJ during the collision, the cross sections for the destruction of an orientation (σ₁) and an “octupolarisation” (σ₃) could be calculated. For the even isotopes the following ratios were derived: σ₁/σ₂=0.76 ± 0.07 and σ₃/σ₂=1.08 ± 0.09.     

Evidence for the coexistence of spherical and deformed states in38Ar

The³⁸Ar levels at E_x=5350, 7289 and 9341 keV have been investigated using the³⁵Cl(α,pγ) reaction at E_α=l4 and 14.5 MeV. From particle-γ-ray angular correlations the spin assignments J(5350)=4, J(7289)=6,4 and J(9341)=8,6,4 have been obtained. Life-time measurements using the Doppler-shift attenuation method yielded τ(9341)=106±25 fs and τ(7289)=77±30 fs, while the lifetime τ(5350)=200±50 fs was known previously. All levels have positive parity and decay by enhanced E2 transitions. Hence we propose that they are the J^π=4⁺, 6⁺ and 8⁺ members, respectively, of a K^π=0⁺ rotational band which has the E_x=3377keV, J^π=0⁺ and the 3937 keV, J^π=2⁺ levels as further members. The enhancement of inband E2 transitions is 30 _?6 ⁺¹⁰ W.u. (4→2), 35 _?14 ⁺³⁰ W.u. (6→4) and 20–36 W.u. (8 → 6), respectively, yielding an average intrinsic quadrupole moment Q₀=850 _?125 ⁺²⁰⁰ mb. The moment of inertia is given by h²2θ=92 keV. The present data are in good agreement with the predictions of a deformed state in³⁸Ar that coexists with the spherical states.     

Properties of the 3− first excited state in the doubly closed shell nucleus146Gd

Conversion electron measurements confirm the 3^? assignment recently proposed for the 1579 keV first excited state in¹⁴⁶Gd. Fromγγ- ande ^? γ-coincidence data the half life of that state has been determined asT _1/2=1.06±0.12 ns.     

Anregung gebundener Atomzustände durch die plötzliche Zentralfeldänderung beim β−-Zerfall des Kerns

By the sudden change of nuclear charge during β^?-decay the daughter-ion is ionized or excited with probabilities of the order of some percent; other processes in the electron shell may be neglected, therefore unperturbed excitations can be measured by detecting photons emitted from the decaying excited atomic states in delayed coincidence with β^?-particles as is shown in an earlier paper for the Kr 85-β^?-decay. More extensive measurements of the photonemission after this decay give results in good agreement with theoretical predictions. Mostly such photons are observed, which can be emitted after a monopol-excitation, for which the selectionrulesΔ J=0 andΔ l=0 are valid. The total excitationprobability into both 5p(J=0)-states of Rb II is found to be P(4p?5p)=5,6±1,0%. The lifetimes of these two states are measured (correspondingly) to be τ=7,6 ±0,5 nsec, from which the reduced matrixelements ¦〈5p∥D∥5s〉¦²=18,9±3,2 and ¦〈5p∥D∥4d〉¦²=10,4 ±1,8 a.u. are calculated.     

The scattering of slow neutrons by phosphorus and nitrogen

The coherent scattering lengthsb and the free cross sections for the scattering of slow neutrons by P and N were measured on powdered samples. From the results we derived data for the incoherent cross sections and for the spin state scattering lengths. We found for phosphorus:b=5.13±0.01 fm, σ_free=3.134±0.010b and σ_inc=0.006±0.016b, and for nitrogen:b=9.36±0.02 fm, σ_free=10.03 ±0.08 b and σ_inc=0.4±0.1 b. Derived values for resonance parameters of N are given.     

Conformation and dipole moment of tetrahydropyran-4-one by microwave spectroscopy

The microwave spectrum of tetrahydropyran-4-one has been studied in the frequency region 18 to 40 GHz. The rotational constants for the ground state and nine vibrationally excited states have been derived by fitting a-type R-branch transitions. The rotational constants for the ground state are (in MHz) A = 4566.882 ± 0.033, B = 2538.316 ± 0.003, C = 1805.878 ± 0.004. From information obtained from the gas-phase far-infrared spectrum and relative intensity measurements, these excited states are estimated to be ～ 100 cm^?1 above the ground state for the first excited state of the ring-bending and ～ 185 cm^?1 for the first excited state of the ring-twisting mode. Stark displacement measurements were made for several transitions and the dipole moment components determined by least-squares fitting of the displacements: (in Debye) |μ_a| = 1.693 (0.001), |μ_b| = 0.0, |μ_c| = 0.300 (0.013) yielding a total dipole moment μ_tot = 1.720 (0.003). A model calculation to reproduce the rotational parameters indicates that the data are consistent with the chair conformation.     

Ground state and singlet excited state of laser dye DCM: Dipole moments and solvent induced spectral shifts

The solvent-induced shifts of the absorption and emission spectra of 4-dicyanomethylene-2-methyl-6-p-dimethyl-amino-styryl- 4H-pyran (DCM) have been studied in a variety of solvents. The absorption spectrum of its first singlet excited state has been determined in methanolic solution (λ_max=455nm , ϵ_max=6.2×10⁴ 1 mol^-1 cm^-1).     

Lifetime measurements in99Sr and100Zr

The lifetime of the first excited state in⁹⁹Sr has been determined by the delayed γ-γ coincidence method. The value of t_/2=0.58(9) ns corresponds to a deformation parameter ß=0.38(4). The deduced z> value confirms the previously proposed ν[411]3/2 Nilsson assignment for the⁹⁹Sr ground state. In addition, lifetime values for the 2⁺ (t_1/2=0.40(8) ns) and 0⁺ (t_1/2=5.36(23) ns) states in¹⁰⁰Zr are obtained, which deviate from older measurements and indicate a larger deformation of ß=0.39(4).     

Nuclear larmor precession of the 14 keV state of57Fe in α-iron following the reaction56Fe (d,p)57Fe

The spin precession of the 14 keV state of⁵⁷Fe, excited by the⁵⁶Fe(d,p) reaction was observed in ferromagnetic Fe. The data yield a magnetic field of ? 330±4 kG and a relaxation time τ _r > 500 ns at room temperature.     

Experimentelle Untersuchungen am Elektroneneinfang des Mangan 54 und Zink 65

The electron capture decay of Mn 54 and Zn 65 was investigated using Na I(Tl)-detectors. Spectroscopic-coincidence techniques were employed to examine theK-electron capture rates of Mn 54 and Zn 65, the branching ratio and positron rate of Zn 65. The experimental results are:P _k ω _k (Mn)=0.2492±0.0017,P _k ω _k (Zn)=0.3927±0.0026,EC ^* /EC ⁰(Zn)=53.2±1.0/46.8±1.0,γ/β ⁺=35.1±1.7,K ⁰/β ⁺=27.7±1.5. Thus electron capture to the excited state of Cu 65 occurs to the extent of 52.4±1.0% while electron capture and positron decay to the ground state were found to be associated with 46.1±1.0% and 1.49±0.05% of the disintegrations. These data partly disagree significantly from measurements of other authors. Using the fluorescence yieldsω _k (Cr)=0.279 andω _k (Cu)=0.4425, deduced from other measurements, values ofL+M/K of electron capture to the excited state could be derived:L+M/K(Mn 54)=0.120±0.015 andL+M/K(Zn 65)=0.127±0.015. These ratios agree with the calculations ofBahcall. The half-lives of Mn 54 and Zn 65 have been determined to beT _1/2(Mn 54)=312±5d,T _1/2(Zn 65)=243±4d The energy of the Zn 65-γ-rays was measured with a Ge(Li)-counter:E ^γ=1115.5±0.5 keV.