Atomic level

Allen L and Eberly J H 1987 Optical Resonance and Two-Level Atoms (New York Dover)... 

Here all couplings are ignored except the direct couplings between the initial and final states as in a two-level atom. The coupled equations to be solved are... 

A sense of scale is important for understanding how chemistry at the macroscopic level is related to the behavior of atoms at the microscopic level. Atoms are extraordinarily small, and there are vast numbers in even very tiny objects. The diameter of a carbon atom is only about 150 trillionths of a meter, and we would have to put 10 million atoms side by side to span the length of this dash -. Even a small cup of coffee contains more water molecules than there are stars in the visible universe. 

Consider a two level atom that initially has a ground state n containing N atoms and an empty upper state m. The atom is then excited by a radiation field tuned to the transition v = Wm — W /h, where hiy kT. In equilibrium, — mn m A i where... 

EELS Electrons Atomic level Atomic level Esp. Z < 10 Yes Yes... 

Our multi-level carbon model atom is adapted from D. Kiselman (private communication), with improved atomic data and better sampling of some absorption lines. The statistical equilibrium code MULTI (Carlsson 1986), together with ID MARCS stellar model atmospheres for a grid of 168 late-type stars with varying Tefj, log g, [Fe/H] and [C/Fe], were used in all Cl non-LTE spectral line formation calculations, to solve radiative-transfer and rate equations and to find the non-LTE solution for the multi-level atom. We put particular attention in the study of the permitted Cl lines around 9100 A, used by Akerman et al. (2004). 

Some insight into the problem can be gained by examining (m) for a two-level atom or molecule (8)... 

Electron energy levels atomic spectra, quantum numbers, atomic orbitals... 

Light emitted from a mercury lamp is caused by electronic transitions from higher-energy-level atomic orbitals to lower-energy-level atomic orbitals. The electronic transitions are subject to certain constraints known as selection rules ... 

Luminescence is, in some ways, the inverse process to absorption. We have seen in the previous section how a simple two-level atomic system shifts to the excited state after photons of appropriate frequency are absorbed. This atomic system can return to the ground state by spontaneous emission of photons. This de-excitation process is called luminescence. However, the absorption of light is only one of the multiple mechanisms by which a system can be excited. In a general sense, luminescence is the emission of light from a system that is excited by some form of energy. Table 1.2 lists the most important types of luminescence according to the excitation mechanism. 

In this section, we will study the absorption and emission probabilities for a single two-level atomic center that is illnminated by a monochromatic electromagnetic wave. 

X. Chen, 1. Lizuain, A. Ruschhaupt, D. Gudry-Odelin, and J. G. Muga, Shortcut to adiabatic passage in two- and three-level atoms. Phys. Rev. Lett, 105(12) 123003—123006(2010). 

Exercise. A two-level atom is subject to a random field acting on its dipole moment, so that the Hamiltonian is... 

Exercise. For the same two-level atom show that the autocorrelation function of the dipole moment p (the second of the two matrices in (2.20)) is... 

This describes a two-level atom interacting with a heat bath such that b2/a2 = exp[—j812]. Exercise. An alternative form of (5.6) is... 

D. A. Hutchinson, K. J. Woloschuk, and C. Mavroyannis, Physica 123C, 319 (1984). Third-Order Nonlinear Spectra of a Strong Bichromatic Field Interacting with a Three-Level Atom in a V Configuration. 

Fluorescence is spontaneous radiation that arises because of the stimulation of an atomic or molecular system to energies higher than equilibrium. This is illustrated in Figure 1 for a simple two-level atom. The atom is excited by absorption of a photon of energy hv. If the fluorescence is observed at 90° to a collimated excitation source, then a very small focal volume may be defined resulting in fine spatial resolution. The fluorescence power an optical system will collect is... 

At laser intensities sufficient to saturate the le-2e transition, the stimulated emission and absorption processes which couple the levels are fast relative to collisional transfer processes, and a quasi-equilibrium balance (e)/Np(e)] is quickly established. If the total population of levels le and 2e is approximately constant during the laser pulse, the upper level population 112(e) can be reliably related to Np(e)0 using an analysis similar to a two level atomic model (1, 2, 3). ... 

Participation of both the hydroxide and hydride is found to be the case for both alkalis. The analysis is unsatisfactory with the inclusion of solely the hydroxide or the hydride. An extension of the usual 2 or 3-level atomic model (2,12-14) to incorporate these chemical schemes is indicated in Figs. 1 and 2 and has been analyzed in detail. Assuming sufficient time for the attainment of a steady state distribution, and rapid coupling of the 2Pi/2 and P3/2 states, the model predicts that for sodium under saturated conditions, the fluorescence intensity. If, will vary as... 

Method 3. Saturation Method With Peak Detection. In this method, developed by (imenetto and Winefordner2,3, it is necessary to excite fluorescence 3+1 with 1+3 and a short time later (< 1 ys) excite 3+1 with 2+3. In this case the atomic system effectively acts on a 2-level atom since excitation and measurement of fluorescence is done at the peak of the excitation pro-fil prior to relaxation of the system to a 3-level steady state process The temperature here is related simply to the ratio BP /Bp and statistical weights of the levels and is independ-r3+l... 

Spatial density profiles of atomic (and molecular) species can also be made via saturation fluorescence approaches. For a "2-level" atom, like Sr, a plot of 1/Bp vs 1/E (Bp is the fluorescence radiance, in J s 1m-2sn l, and Ex is the excitation spectral irradiance, in J s nT nm ) allows estimation of the quantum efficiency, Y of the fluorescence process (and thsu estimation of "radiationless" rate constants) and the total number density nj, of the species of interest by means of... 

Isotope balancing can be carried out at two levels, atom-wise or molecule-wise. In the case of isotope balancing on the level of carbon atoms, fractional enrichments are used for estimating the fluxes. Thus, the sum of labeled carbon... 

OPTICAL RESONANCE AND TWO-LEVEL ATOMS, L. Alien and J.H. Eberly. Clear, comprehensive introduction to basic principles behind all quantum optical resonance phenomena. 53 illustrations. Preface. Index. 256pp. 5)4 x 8H. 

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