Strong Coupling Field Research Articles

Matched pulses and electromagnetically induced transparency for the interaction of laser pulse pairs with a double-vee system

We demonstrate the occurrence of electromagnetically induced transparency with pulse matching in the propagation of two probe pulses through a double-vee (DV) system prepared by a pair of strong coupling fields. Pulse matching is connected to the phenomenon of coherent population trapping. We show that the space-time evolution of the probe pulses is determined by a pair of normal modes that describe the propagation of the pulsed excitation through the medium. The establishment of the pulse-matching propagation regime and the transparency for the probe pulses are related to the absorption properties of the normal modes.

Quantum interference in nonlinear optical processes using strong-field coupling in atomic hydrogen

We have systematically analyzed the sum-frequency generation and multiphoton-ionization process with strong-field coupling and quantum interference, using atomic hydrogen as a test medium. Experimental results have well confirmed the theoretical predictions.

Continuous-wave electromagnetically induced transparency: A comparison of V, Lambda, and cascade systems.

A theoretical and experimental investigation has been carried out into the viability of V-type, \ensuremath{\Lambda}-type, and cascade systems within rubidium for the observation of electromagnetically-induced transparency (EIT). A \ensuremath{\Lambda}-type system is also discussed where EIT is induced on a two-photon transition. Continuous-wave single-frequency titanium sapphire lasers have been employed to provide the applied optical fields. It is found that systems that have a strong coupling field resonant with the 5${\mathit{S}}_{1/2}$ ground state suffer from complicating optical pumping mechanisms that tend to mask EIT windows. It is also found that wavelength matching of the applied optical fields enhances the observation of EIT since this results in a reduced residual Doppler linewidth of the atomic system.

Sum-frequency generation using strong-field coupling and induced transparency in atomic hydrogen.

The sum-frequency generation process using strong-field coupling and quantum interference is described systematically using atomic hydrogen both in theory and experiment. It is shown that strong coupling at the 3p-2s transition creates destructive interference to reduce the linear susceptibility at the resonant 3p\ensuremath{\leftarrow}1s transition. Simultaneously, two-photon coupling of the 2s and 1s states produces constructive interference to resonantly enhance the nonlinear susceptibility for sum-frequency generation at the 3p\ensuremath{\rightarrow}1s (Lyman-\ensuremath{\beta}) transition. Experimental results clearly demonstrate the theoretical predictions. When the Rabi frequency for the 3p-2s coupling exceeds the Doppler tail of the medium, the photoion signals on resonance are suppressed significantly because of induced transparency. The generated Lyman-\ensuremath{\beta} radiation grows rapidly by a factor of 250 at an atom density of ${10}^{15}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ and interaction length of 3.5 cm, resulting in a conversion efficiency of 2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$.

Spin-valve sensors with domain control hard magnet layers

We have fabricated unshielded narrow-track NiFe/Cu/NiFe/FeMn spin-valve sensors with a height of 2 /spl mu/m and a track-width of less than 2 /spl mu/m using CoCrPt hard magnets (4/spl pi/Mr=5500 G, Hc=1000 Oe) as a domain control layer. Barkhausen noise was completely suppressed by a longitudinal biasing field from the CoCrPt layers. The bias state was improved by applying a strong ferromagnetic exchange coupling field of 30 Oe between the free and pinned NiFe layers through a 14 /spl Aring/-thick Cu interlayer. We have also fabricated shielded CoCrPt magnet-biased spin-valve read heads with a track-width of 1.7 /spl mu/m. The heads had no Barkhausen noise and very low crosstalk noise.

Doubley-resonant coherent coupling of infrared radiation via intersubband transitions in quantum wells

The influence of a strong coupling field on the linear response of a modulation-doped quantum well to a weak probe field is studied theoretically for the case when the coupling field frequencies are comparable to those of bound-bound and bound quasi-bound transitions within the conduction subbands. Model calculations suggest that line-center reductions in the ground-to-coupled excited-subband absorption of up to 80% can be coherently induced with CO2 laser intensities of ∼ 20 MW/cm2. The effect requires the infrared coupling field to be polarized in the growth direction, and the nature of the modifications in the linear response depends strongly oft the parity and relaxation rates of the excited subband states.

Strong-coupling field theory and soliton doping in a one-dimensional copper-oxide model.

A field theory for the strong-coupling limit of a one-dimensional copper-oxide model is obtained from a weak-coupling point of view. Complementary aspects of strong correlations and band motion are incorporated in a natural way. Doping induces soliton or antisoliton charge excitations into a state with explicity broken chiral symmetry. The solitons or antisolitons have divergent superconductive pairing-correlation functions and various properties reminiscent of doped holes or electrons in high-temperature superconductors.

The delta expansion - a new method for strong-coupling field theories

A review is given of recent developments in the δ expansion.

Calculation of the spin-lattice coupling coefficientG44from two cases for Ni2+ion in cubic crystals

Abstract The spin–lattice coupling coefficients G 44 for Ni2+ ions in cubic crystals (MgO, CaO) have been calculated for two cases. The two calculated results for each crystal are not only close to each other, but also in agreement with the experimental values. In this sense, it follows that the formulae for the zero-field splittings D in a trigonal field and E in a rhombic field for d8 ions based on the strong-field coupling scheme are consistent and suitable, and that the inspection method for the formulae of zero-field splittings by comparing the coefficient G 44 calculated from two cases is, to a certain degree, useful and convenient.

Nonlinear optical processes using electromagnetically induced transparency.

We show that by applying a strong-coupling field between a metastable state and the upper state of an allowed transition to ground one may obtain a resonantly enhanced third-order susceptibility while at the same time inducing transparency of the media. An improvement in conversion efficiency and parametric gain, as compared to weak-coupling field behavior, of many orders of magnitude is predicted.

Calculation methods for the spin-lattice coupling coefficient F 44 in cubic symmetry for two cases

Similar to the case of coupling coefficients G ij , the relationships between the spin-lattice coupling coefficients F ij ( F 11, F 12 and F 44) in cubic symmetry and the g-factors in cubic and low symmetries have been found and hence simple and unified methods of calculating these coefficients from the formulas of the anisotropic g-factor are given. On this basis, the coefficient F 44 can be calculated very easily for two cases, i.e., for the g-factor formulas in trigonal field and for those in rhombic field. Thus, we can, in a certain degree, check whether the formulas of the g-factor in trigonal and rhombic symmetries are consistent and reliable by comparing the values of F 44 calculated for the two cases. As an example, the formulas of anisotropic g-factor for d 8 ions based on the strong-field coupling scheme have been inspected. Because the calculated values of F 44 for MgO:Ni 2+ crystal for the two cases are not only close to each other, but also in good agreement with the estimated experimental value, these formulas for the g-factor in trigonal and rhombic fields obtained by different authors can be regarded as reasonable.

Further remarks on particlelike solutions in spinor-connection theory.

In a recent work the author presented a numerical solution for a neutral pionlike particle in spinor-connection theory. Here, using a more analytical approach and an improved numerical method, that solution is studied in greater and refining detail. A new solution for an electrically charged pionlike particle is also given. The results obtained suggest that the electromagnetic and strong-field coupling constants are closely equal.

Energy matrices of irreducible representations of point group D2for electron system d5and the electronic spectrum of ion Fe3+in silicate garnets

The electronic spectrum of the Fe3+ ion in silicate garnets is calculated by means of the energy matrices of irreducible representations of the point group D2 for the electron system d5 in the strong-field coupling scheme. The result obtained is in good agreement with the experimental data. From this, it is suggested that the Fe3+ ions in this kind of silicate garnet are mainly located at the sites of D2 symmetry, rather than those with symmetry Oh or Td assumed previously.

The spin-forbidden spectrum of Fe2+in silicate garnets

A strong-field coupling scheme of 'once-diagonalisation' is proposed to calculate the spin-forbidden bands of the Fe2+ ions located in the D2 symmetrical eightfold site in silicate garnet. The method is to establish the energy matrices of the strong-field terms of the D2 point group of the d4(d6) electron configuration directly, so as to diagonalise simultaneously the crystal field (as a whole) and the electrostatic repulsion energy between the electrons. According to this scheme, making use of the observed data of the spin-allowed spectrum, the authors have, using only one adjustable parameter B (with C=4B), obtained all the spin-forbidden bands. Their results are in quite good agreement with the twenty bands observed. As to the spin-allowed spectrum, the assignment of Newman et al. (1978) is used in their calculations and supported by their theoretical results.

Effects of lower-symmetric crystal fields in the intermediate-coupling scheme for the transition-metal complexes

A generalized intermediate-coupling scheme was developed for the transition-metal ions embedded in cubic (octahedral or tetrahedral) crystal fields. This scheme is useful for the cubic complexes of $4d$ and $5d$ ions and in this context the advantage (in physical interpretation and in consequent simplicity in calculations) of this scheme over the conventional strong-field coupling scheme was clearly demonstrated. In this paper, this new scheme has been further generalized to include a lower-symmetric (tetragonal or trigonal) crystal field, which is essential in dealing with most of the complexes where deviations from the cubic symmetry are considerable. As in previous papers, one can easily find out the obvious advantages of this scheme which allows one to arrive at the useful energy levels and wave functions with the minimum amount of labor in calculations. The truncation in the calculation by using only the group of lower-lying energy states (which, according to the very nature of the scheme, are easily recognizable) is the salient feature of the scheme, and to show in passing the validity of this method, we have, at the end, considered the case of a ${d}^{1}$ system with the tetragonal (${D}_{4h}$) distortion and the results obtained thereby are compared with the corresponding exact results appearing elsewhere.

Application of the intermediate-coupling scheme to a5d4system,K2OsCl6

In this paper we have applied the generalized intermediate-coupling scheme, developed by us, to a $5{d}^{4}$ system, ${\mathrm{K}}_{2}$Os${\mathrm{Cl}}_{6}$, and have demonstrated very clearly the great convenience and simplicity of this scheme compared to the usual strong-field coupling scheme which was applied earlier in studying this complex. Practically without any labor we have been able to get a very close agreement with experiment for which the conventional approach needed to diagonalize matrices of large dimensions. This shows the distinct advantage of the present model in studying the optical and magnetic properties of the complexes of the palladium and platinum groups.

Intermediate-coupling scheme for many-electron systems of the complexes of the transition-metal ions

The generalized theory of the intermediate-coupling scheme has been developed for the many-electron systems of the second and third series of the transition-metal-ion octahedral complexes. The theory has been developed for the general configuration, $k{d}^{n}$ ($k=3, 4, 5$; $n=2, \dots{}, 9$) but has been presented up to $n=5$. The transformation matrices for the remaining ${d}^{10\ensuremath{-}n}(nl5)$ configurations can be easily found from those of ${d}^{n}(nl5)$ by using the well-known principle of electron-hole complimentarity. To show the enormous simplicity and great advantage over the strong-field coupling scheme so long used in such cases, the ${d}^{3}$ configuration has been treated by this method as an application. At the end some typical magnitudes of the parameters like $\mathrm{Dq}$, $\ensuremath{\zeta}$, $B$, and $C$ have been used to find the energy levels and the paramagnetic susceptibility for ${\mathrm{K}}_{2}$Re${\mathrm{Cl}}_{6}$. The beauty and importance of this scheme lies in the fact that as one switches off the spin-orbit interaction one gets results identical with those of Tanabe and Sugano, and further, if one also switches off the crystal field but retains only the interelectronic repulsion term one gets the results coinciding with those of Racah in atomic spectroscopy.

Singular-perturbation—strong-coupling field theory and the moments problem

Motivated by recent work of Bender, Cooper, Guralnik, Mjolsness, Rose, and Sharp, a new technique is presented for solving field equations in terms of singular-perturbation---strong-coupling expansions. Two traditional mathematical tools are combined into one effective procedure. Firstly, high-temperature lattice expansions are obtained for the corresponding power of the field solution. The approximate continuum-limit power are subsequently obtained through the application of Pad\'e techniques. Secondly, in order to reconstruct the corresponding approximate global field solution, one must use function-moments reconstruction techniques. The latter involves reconsidering the traditional moments problem of interest to pure and applied mathematicians. The above marriage between lattice methods and reconstruction procedures for functions yields good results for the ${\ensuremath{\varphi}}^{4}$ field-theory kink, and the sine-Gordon kink solutions. It is argued that the power are the most efficient dynamical variables for the generation of strong-coupling expansions. Indeed, a momentum-space formulation is being advocated in which the long-range behavior of the space-dependent fields are determined by the small-momentum, infrared, domain.

Electrostatic interaction for arbitrary point groups, configurations, and coupling schemes

AbstractThe electrostatic interaction for arbitrary symmetry (including non‐simply reducible point groups), different coupling schemes, and several open shells is discussed from a common viewpoint using the particle‐number representation (second quantization). The different coupling schemes simply arise from a different interpretation of the relevant symmetry group. Using the adjective CFPS of the preceding paper, the interaction within several open shells can be calculated. In the case of one‐center expansions like ligand field theory the many‐particle matrix elements are directly expressed by the radial Slater integrals using isoscalar factors. An example of the formalism is worked out. By the way the unitary transformations between strong and weak field coupling schemes are expressed recursively in the number of particles.

Energy diagrams based on complete ligand field calculations for arbitrary point groups in strong-field coupling

Computational methods are described for effecting complete ligand field calculations, inclusive of spin-orbit coupling, on the strong-field {( c N ) Sl' S a S l' L ; l' b} basis. Plotter routines which subsequently execute complet e energy diagrams of Tanabe-Sugano type are presented. The procedures operate for all d N configurations, N = 1, 2, …, 9, and make full use of the point group symmetry of the system, G⊂ SO(3). The relations employed for calculation of the matrix elements are listed and methods to obtain all required coefficients are given. The resulting diagrams are required for the interpretation of spectra and paramagnetic properties of d N systems.