Correlation between the intensities of intermultiplet electric dipole transitions and the fine features of the stark structure of multiplets of Pr3+ ions in the LaCl3 compound

The Stark structure of the multiplets of Pr³⁺ ions in the LaCl₃ compound is described and the even and odd parameters of the crystal field, as well as the covalency parameters, are determined in the approximation of an intermediate interconfiguration interaction. The covalency parameters thus obtained agree well with the parameters calculated in the framework of microscopic models. The intensity parameters of intermultiplet electric dipole transitions are calculated using the odd parameters of the crystal field and the covalency parameters. The results of the calculations are in satisfactory agreement with the experimental data. This allows the conclusion that there is a correlation between the fine features of the Stark structure of the multiplets and the intensities of the intermultiplet electric dipole transitions.     

Spectroscopic Properties of LiNbO<Subscript>3</Subscript>:Tm<Superscript>3+</Superscript> Crystal in the 1650–1970 nm Wavelength Range

Taking into account the Stark structure of optical spectrum of the impurity ion, the theoretical study of spectroscopic properties of LiNbO₃:Tm³⁺ crystal in the wavelength range of 1650–1970 nm was carried out. The wave functions of the Stark sublevels of both ground ³H₆ and the first excited ³F₄ manifolds of the Tm³⁺ ion were constructed in the LSJM-representation, the line strengths induced by indirect electric-dipole transitions were calculated, and the main spectroscopic characteristics of emission and absorption spectra of impurity ion were determined.     

Interaction of Wannier–Stark levels in a wide well superlattice

We have investigated the energy spectrum of a superlattice with wide quantum wells under the bias of an electric field perpendicular to the superlattice layers. By using photocurrent spectroscopy, transitions of Wannier–Stark levels for the various electron and hole states are observed, and at low fields, further structures corresponding to miniband edge transitions are found. Various anticrossings could be observed at higher and lower electric fields. The anticrossings at high electric fields are due to energy alignment of different electronic sublevels in adjacent wells. The anticrossing structures at low fields could be interpreted as resonances between intrawell and interwell excitonic Wannier–Stark states with equal sublevel states, where the anticrossing is caused by differences in exciton binding energy. Fitting of transitions and anticrossings was done by using a semi-empirical model and we have extracted relevant fitting parameters like the quantum-confined Stark coefficient, binding energies for the excitonic Wannier–Stark levels and the resonant coupling strength for states involved in the various anticrossing transitions. Finally, insight into the excitonic influences on the coupling of the WS states could be obtained by comparing the fitted parameters for the various transitions.     

Intensities of inter-Stark transitions in activated crystals

A scheme of calculation of line strengths for indirect electric dipole transitions between Stark states of impurity ions in dielectric crystals is proposed. It is shown that knowledge of the three semiphenomenological Judd-Ofelt parameters of a crystalline system is sufficient for quantitative calculations. The formulas obtained were approved for YAG:Nd³⁺ crystals based on calculation of the spectroscopic characteristics of the lines of the inter-Stark transitions ⁴ F _3/2 → ⁴ I _9/2 and ⁴ F _3/2 → ⁴ I _11/2.     

Polarized spectral analysis of Er3+ ions in biaxial Bi2(MoO4)3 crystal

An Er³⁺:Bi₂(MoO₄)₃ single crystal has been grown by the Czochralski technique. The Stark sublevels of the ⁴I_15/2 and ⁴I_13/2 multiplets of Er³⁺ ions in the crystal were determined. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curve of the crystal were measured at room temperature and the relevant spectroscopic parameters, including the Judd–Ofelt intensity parameters, spontaneous emission probability, fluorescence branching ratio, radiative lifetime, and stimulated emission cross section, were estimated. The effect of re-absorption on the spectroscopic parameters was discussed. When the crystal was excited at 977 nm, up-conversion green fluorescence was observed and discussed.     

顺磁物质CeF3磁光Faraday效应及其温度特性的量子理论

本文计算了顺磁物质CeF₃因Ce³⁺离子从基态能级4f至5d的电偶极跃迁产生的Fara-day旋转。讨论晶场对Ce⁺³离子4f和5d能级的影响,通过唯象地引入一个与磁化强度M成正比的“附加磁场”H_m=λM,由此获得4f离子在外加磁场和“附加磁场”的共同作用下的一级Zeeman分裂。经劈裂后的两个子能级上各自产生左、右圆偏振光激发的电偶极跃迁,导致磁光Faraday效应。对于波长为0.6328μm的入射光,在60—300 关键词：     

Perturbation theory for the intensity of Stark lines of a hydrogen atom

Perturbation theory for the wave function of a hydrogen-like atom in a homogeneous electric field of strength F makes it possible to obtain the Rayleigh-Schrödinger series with the coefficients of F ^N (N=0, 1, 2,...) being linear combinations of the Sturm function, which represents the unperturbed state, with 8N ² functions of the corresponding complete set with indices adjacent to the parabolic quantum number of the initial level. A method for recursive analytic calculation of the coefficients of the linear combination for any order N is developed. General expressions for corrections to the matrix elements and intensities of the radiation transitions between Stark sublevels are obtained. Analytic formulas and numerical values of the corrections up to the fourth order for the Lyman and Balmer series are presented. A comparison with the available data for transitions between the Stark components of Rydberg states is given.     

Crystal field and exchange interactions in the SmFe3(BO3)4 multiferroic

The optical spectra of oriented SmFe₃(BO₃)₄ single crystals are studied in the region of the f-f transitions in the Sm³⁺ ion by Fourier spectroscopy. The energies, the symmetry properties, and the exchange splittings of the Stark sublevels of the ground and 17 excited multiplets of the Sm³⁺ ion in a crystal field of symmetry D ₃ are determined from the measured temperature dependences of polarized-radiation absorption spectra. The parameters of the crystal field acting on samarium ions and the parameters of the exchange interaction between Sm³⁺ and Fe³⁺ ions are found. The anisotropy of the effective exchange interaction is shown to be substantially stronger than the magnetic anisotropy, due to a strong crystal-field-induced mixing of the ground and excited multiplets.     

Peculiarities of Er3+ photoluminescence in halogen-doped amorphous silica

The spectra and photoluminescence kinetics of Er³⁺ ions embedded in amorphous fluorine- and chlorine-doped silica matrices synthesized by surface-plasma chemical vapor deposition were investigated at 27–300 K. Luminescence was excited with an Ar⁺ laser at a wavelength of 514.5 nm and with a diode laser at a wavelength of 975 nm. Narrow and well-expressed components of Stark sublevels with a small contribution of inhomogeneous broadening intrinsic to Er³⁺ ions in crystalline rather than amorphous matrices were revealed and identified in photoluminescence spectra. The structure of Stark sublevels was well-resolved at low temperatures. The presence of the well-resolved Stark structure in spectra was indicative of stable anion complex formation in Er³⁺ environment presumably associated with halogen incorporation. This environment was formed at a stage of the low-temperature plasma-chemical synthesis and was destroyed at glass fusion.     

Probabilities of radiative transitions between Stark states in orthohelium

The wavefunctions, matrix elements, and probabilities of radiative transitions between Stark sub-levels of atomic multiplets are calculated as a function of the strength of a dc electric field. The general expressions for the wavefunction of a multiplet state in a field obtained by perturbation theory for close-lying levels with the use of completely reduced Green’s function allow one to determine the field dependence of both the dipole-allowed and dipole-forbidden radiation amplitudes. A decomposition of the second-order amplitude for the transition between fine-structure sublevels of two levels of equal parity into irreducible components is obtained. Numerical calculations of the probabilities of radiative transitions between triplet states of helium show the possibility of experimental observation of the emergence and vanishing of Stark lines of radiative transitions in the vicinity of anticrossing fields.     

A precision measurement of the hyperfine structure of87Sr+

The ground state hyperfine splitting of⁸⁷Sr⁺ was measured with a precision of 1×10^–8. The experiments were performed with an RF ion trap connected to an ISOL (isotope separator on-line), where all the possible transitions between Zeeman sublevels were observed by a laser-microwave double resonance method. The magnetic dipole hyperfine constant was determined to beA=–1 000 473.673 (11) kHz.     

环境辐射对原子高激发能级Stark态寿命的影响

在外电场中用激光两步激发使Na原子在待测Stark态（n=17，m=0）上实现布居．用延迟脉冲场电离方法测量了部分Stark态的寿命及环境黑体辐射对其实际寿命的影响，并与理论计算值作了比较．实验和计算表明：对n=17的Stark簇各能态，室温下环境黑体辐射引起的受激跃迁对其寿命的影响与自发辐射跃迁已达同一数量级．寿命越长的Stark态，黑体辐射的影响程度越大，这一因素连同Stark混合效应均使同一Stark簇内各能态实际寿命的差异变小． 关键词：     

Degenerate cascade fluorescence: Optical spectral-line narrowing via a single microwave cavity

For a three-level atom, two nondegenerate(even microwave and optical) electric dipole transitions are usually allowed; for either of these, the fluorescence spectra are well-described in terms of spontaneous transitions from a triplet of dressed sublevels to an adjacent lower-lying triplet. When the three dressed sublevels are equally spaced from each other, a remarkable feature known as degenerate cascade fluorescence takes place, which displays a five-peaked structure. We show that a single cavity can make all the spectral lines extremely narrow, whether they arise from cavity-coupled or cavity-free transitions. This effect is based on intrinsic cascade lasing feedback and makes it possible to use a single microwave cavity(even a bad cavity) to narrow the spectral lines in the optical frequency regime.     

Specific features of magneto-optical spectra of Tb<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript>

The spectra of magnetic circular dichroism in the range of the ⁷ F ₆→⁵ D ₄ absorption band and the spectra of magnetic circular polarization of luminescence in the range of the ⁵ D ₄→⁷ F ₅ band in the terbium-gallium garnet Tb₃Ga₅O₁₂ are studied at a temperature of 80 K. The optical transitions between the Stark sublevels of the ⁷ F ₆, ⁷ F ₅, and ⁵ D ₄ multiplets are identified based on the analysis of the magneto-optical and optical spectra. It is shown that the experimentally determined symmetry and energy of the Stark sublevels of these multiplets confirm the results of numerical calculations of the energy spectrum of the Tb³⁺ rare-earth ion in terbium-gallium garnet.     

The signs of the valence bond wave functions in an alternant hydrocarbon

The infrared spectrum of ¹²CD₃F from 1040 to 1200 cm^-1 has been analysed using a new program which diagonalizes the complete interaction hamiltonian matrix for the v ₂ and v ₅ ro-vibrational levels. The program fits simultaneously the microwave, laser Stark and diode spectra and over 800 transitions in the Nicolet FTIR spectrum. A comparison of the calculated and observed infrared spectra shows the phases of the dipole moment derivatives to be of opposite sign. Several new Stark spectra have been assigned.     

Magnetic circular polarization of luminescence of dysprosium-yttrium aluminum garnet Dy0.2Y2.8Al5O12

Magnetic circular polarization of the luminescence of the radiative 4f-4f transitions ⁶ H _15/2→⁶ F _9/2 in dysprosium-yttrium aluminum garnet Dy_0.2Y_2.8Al₅O₁₃ was studied at T=85 K. The revealed features of the spectral dependences of the magnetically polarized luminescence of Dy³⁺ ions are attributed to the quasi-Ising behavior of rare-earth ions in the garnet structure. The symmetry of the wave functions for a number of Stark sublevels of the multiplets of the ground configuration 4f(n) that combine in observed radiative transitions is determined.     

Use of the anomalous Stark effect for the approximate determination of torsional energy splittings

An advantageous use of the anomalous Stark effect for the determination of the torsional energy splittings is proposed. The method is applicable in those cases where the dipole moment component connecting the torsional states of different parity has an experimentally observable magnitude. The analysis of the Stark spectrum observed in the spectrum of the N-cis lone-electron-pair gauche isomer of allylamine is presented as an example. The Stark effects of those transitions (a-type and b-type) which are inside the same vibrational state (0⁺ and 0^?), are used for the fitting of the μ_a, μ_b, and μ_c dipole moment components as well as the torsional energy splitting Δν_tors. The values obtained are compared to more accurate values derived by other methods. The possible use for predicting large torsional splittings is discussed.     

Spectral properties of a Tm:Ho:YAG laser in active mirror configuration

3+ :Ho³⁺:YAG laser is operated in active mirror configuration. This laser is characterised by a rather thin crystal (3 mm thickness in our experiment) and a very short resonator (about 3.2 mm). Therefore this laser is well suited for operation in a single longitudinal mode. Single-frequency operation is demonstrated with and without an intracavity etalon. It is further shown that single-frequency emission is reached with a stable cw emission. With a slight detuning of the outcoupling mirror, spiking can be achieved, resulting in an emission on different lines. The assignment of the observed laser lines to the known transitions between Stark sublevels of the ⁵I₇ and the ⁵I₈ level is discussed and compared with predictions in the literature. Received: 2 December 1997     

Nonlinear level crossing in the infrared transitions of optically pumped far infrared laser media

In conjunction with the Stark field induced power enhancement in optically pumped far infrared lasers, absorption transitions in a degenerate two level system under the influence of an weak static Stark field have been analyed. A third order theory to the density matrix formalism leads to zero field level crossing signals for absorption in rate equation approximation and in Doppler limit. For fast relaxation among Zeeman sublevels, the zero field level crossing signal arises from population effect. Optoacoustic measurements have been carried out on the ₅,^qQ(16,8) absorption line of CH₃OH which produces the familiar 119-m laser with the CO₂ 9P(36) pump line. The optoacoustic absorption signals observed are well reproduced by the theoretical expression.