Nonresonant Transitions Research Articles

On the combined Doppler and pressure broadening of nonresonant spectral lines

An explicit spectral function for nonresonant transitions has been derived that includes pressure broadening, Doppler broadening, and diffusional narrowing. This has been accomplished through a kinetic-equation approach. The kinetic equation has been resolved by using an extension of the Bhatnagar–Gross–Krook collision model to inelastic collisions, characterized by two collision frequencies: one associated with elastic collisions and the other associated with inelastic ones. The high- and low-density limits have been discussed, and the standard formula for Debye relaxation has been reproduced. Finally, a discussion concerning the above aspects and their possible extensions has been included as well.

Radiative trapping and self-reversal of non-resonance transitions in rare gases

A number of 2pi to 1sf non-resonance transitions in rare gases have been studied at high spectral resolution using a new kind of scanning monochromater. It is found that, at certain experimental conditions, many of these lines might be subjected to very strong self-reversal effects. These effects seen on the line shapes are discussed in relation to wavelength measurements and to earlier measurements on the associated radiative lifetimes.

Nonadiabatic effects in multiphoton transitions: A coupled equations study

A coupled equations method is used to examine nonadiabatic effects on two- and three-photon transitions in diatomics. Using C12 as a test case, it is shown that nonadiabatic corrections are less important for virtual (nonresonant) transitions than in the case of resonant transitions. The contributions from virtual transitions diminish with the order of the multiphoton transition. Finally, the present method enables one to calculate transition amplitudes. The phase information in such amplitudes are shown to be useful to identify photon pathways in some multiphoton transitions especially at high intensities where the coupled equations approach enable us to go beyond perturbative methods.

Study of resonance and non-resonance atomic fluorescence transitions in plasma spectrometry

Results obtained with the “atomiser, source, inductively coupled plasmas in atomic fluorescence spectrometry”(ASIA) instrument demonstrate remarkable freedom from spectral interference for elements that exhibit the effect in ICP-AES. Narrow band pass interference filters have been used to select the wavelength of excitation for fluorescence measurements and the resonance and non-resonance spectrum of lead has been recorded. Part per billion sensitivity has been achieved at several non-resonance wavelengths and the system has been shown to be useful in the determination of fluorescence mechanisms. Power line filters and earth chokes have been included in the instrument giving an over-all improvement in the noise levels observed.

Laser-excited atomic fluorescence spectrometry in an atomic absorption graphite tube furnace

A dye laser pumped by an excimer laser was used for laser-excited atomic fluorescence spectrometry (LEAFS) in a Perkin-Elmer HGA-500 graphite tube atomiser. The tube furnace was modified for LEAFS by drilling two 4-mm holes across the centre of the tube. Laser light was either passed down the bore of the tube or across the centre of the tube and fluorescence was detected at a right angle. Atomisation was investigated with and without a L'vov platform. Resonance and non-resonance LEAFS transitions were studied. Detection limits for Ag, Co, Cu, In, Mn, Pb and Tl were 8,500, 400, 80, 80, 7 and 100 fg, respectively. The linear dynamic ranges (relative slope of one) for these elements extended 4–6 orders of magnitude above the detection limit. The relative standard deviation for 14 measurements of 200 pg of lead was 10%.

Resonant and intrastate transitions to the 2+ state in8Be

We have studied resonant, intrastate and non-resonant bremsstrahlungγ-ray transitions leading to the 2+ state in8Be atE x=2.94 MeV. We find aγ-width of Γ γ =0.45 eV for the 4+ state in8Be, corresponding to anE 2 strength of 19 W.u. For the intrastateγ-ray transition within the 2+ resonance we predict a maximum cross section of 2.5 nb atE≈3.3 MeV. An experimental observation of this novel type ofγ-ray emission, however, appears to be difficult due to the dominance of competing resonant and direct capture processes.

Line profile of dual-frequency radio optical resonance with nonlinear optical indication

The line profile and amplitude of dual-frequency radio optical resonance (DFROR) in an absorption cell with three-level atoms inside a laser cavity are analyzed from a theoretical viewpoint. Coherence for a nonresonance optical transition is taken into account. It is shown that the line for nonlinear optical indication can be significantly contracted.

Lifetime of excited atomic states.

In this paper we derive an expression for the lifetime of excited atomic states taking account of contributions due to nonresonant two-photon transitions. Explicit integration of the two-photon emission spectrum is not required. The results are applied to the case of the hydrogen atom.

Glow discharge source atomization for the laser-excited atomic fluorescence spectrometric studies of indium

A demountable glow discharge source has been used for the atomization of the analyte solutions deposited on graphite and copper rod cathodes. Indium atoms are sputtered-atomized from the cathode surface and are excited by a pulsed, frequency-doubled dye laser pumped by the nitrogen laser. Atomic fluorescence measurements were performed using the non-resonance fluorescence transition. The detection limits of indium in aqueous solutions (10μl) deposited on graphite and copper electrodes were 8 × 10 −9 and 11 × 10 −9g, respectively (8 ng and 11ng).

Dipole interaction of a multilevel system with a continuous-wave or Gaussian-pulsed laser.

An algorithm [G. F. Thomas and W. J. Meath, J. Phys. B 16, 951 (1983)] for evaluating the evolution operator of a multilevel system dipole interacting with either a continuous-wave or Gaussian-pulsed source, based on its Riemann product integral representation in conjunction with Frazer's method of mean coefficients, is appraised and extended. Our extension allows for the inclusion of spontaneous decay or a dissociation (or ionization) channel and useful relations are derived for the eigenvalues of the evolution operator for both the continuous wave and the Gaussian pulse. For the latter we now admit an arbitrary phase in the field and we derive a simple relation for cascading the state amplitudes of the system over the duration of an arbitrary number of identical phase-coherent pulses. As part of our appraisal, improvements in the implementation of the algorithm are provided. For a two-level system, the evolution operator is given as the chronologically ordered product of readily computed 2\ifmmode\times\else\texttimes\fi{}2 matrices while for multilevel system it is conveniently evaluated using a resolvent method based on Leverrier's algorithm for computing the Bateman matrices. The asymptotic behavior of the evolution operator and the fluence in the direction of propagation for both the continuous-wave and the Gaussian-pulsed sources are explored. Applications to model two-level systems illustrate the influence of the source's phase and interaction duration on resonant and nonresonant transition probabilities, respectively. The saturation of a two-level system by a train of resonant phase-coherent Gaussian pulses is demonstrated.

Calculation of probabilities of non-resonant transitions in an intense laser field using the first-order magnus approximation in an intermediate representation

The quantum dynamics of non-dissociating diatomic molecules in intense laser fields is investigated using the Floquet method. The time-displacement propagator over the first optical cycle is calculated using the first-order Magnus approximation in an intermediate representation. An application is made to rotational excitation through the upper states. Good agreement with numerical calculations is obtained, except for strong fields near the resonant frequency.

Site selective rare earth spectroscopy in proteins

High resolution laser techniques are shown to spectrally resolve europium substituted calcium ion binding sites of the protein thermoysin. Fluorescence line narrowing techniques are shown to reduce the linewidths by 30% for non-resonant transitions indicating accidental degeneracies limit the spectral resolution attainable.

Optical multiple pulse sequences for multiphoton selective excitation and enhancement of forbidden transitions

In this paper we present novel and simple pulse sequences for enhancing the intensity of forbidden or highly nonresonant optical transitions. These sequences provide a straightforward approach to circumventing the most serious limitation of optical coherent transient spectroscopy: Available laser intensities are often insufficient to excite a significant fraction of the ground state population into desired excited states, either because of large inhomogeneous broadening or, in the case of multiphoton absorption, large anharmonicities. Optical phase modulation (which can be produced by an acousto-optic modulator) or amplitude modulation (which can be produced by an interferometer) with carefully chosen pulse flip angles and delays can effectively remove even very large energy mismatches, thus permitting essentially complete population inversions arbitrarily far from resonance. Coherent averaging theory and computer calculations are used to derive particularly valuable sequences. Pumping enhancement of 103–105 (depending on individual molecular parameters) for these modulated pulse sequences are predicted. Specific applications to multiphoton pumping of local vibrational modes are discussed.

Stark effect in dispersive optical bistability

Stark terms associated with nonresonant transitions are shown to have important consequences when they are incorporated into the theory of dispersive optical bistability for a ring cavity. The perturbing effects of the nonresonant transitions should be detectable in an experiment.

Analytical potential of non-resonance lines for the determination of palladium by graphite furnace atomic absorption spectrometry

Palladium is determined by graphite furnaceatomic absorption spectrometry. 8 non-resonance lines were studied, 4 of which have not been previously reported. The peak shapes and parameters of non-resonance lines are somewhat different from those of the resonance lines. The sensitivity of non-resonance transitions is found to be strongly dependent on the atomization temperature, heating rate of the graphite furnace as well as flow rate and nature of the purge gas used. The peak area sensitivity of the 340.5 nm nonresonance line almost equals that of the 276.3 nm resonance line.

Nonresonance radiationless transitions in polyatomic molecules

The possibility of intramolecular nonradiative decay of an initial state |sO〉 to directly coupled final states {|⌊w〉} far from resonance [i.e. under condition ∈ sO − ∈ ⌊w〉〉 ℏΓ ⌊w(∈ sO)] is investigated. It is concluded that nonresonance transitions can govern and control the radiationless properties of the systems with the large interstate energy gaps.

Sudden rotation approximation for nonresonant transitions in an intense laser field

A quantum mechanical study is made of rotational transitions within the vibrational manifold of a diatomic molecule which is in an intense laser field whose frequency is comparable to the vibrational frequency. An analytic iteration scheme for the time dependent propagator in the sudden approximation is implemented through the third order. The approximations are discussed and an improved scheme is suggested. The third order SRA results for HF rotational transitions are in excellent agreement with exact numerical results.

Resonant cancellation of Brillouin scattering near the indirect gap of α-ZnP2

Resonant Brillouin scattering from longitudinal and transverse phonons has been investigated in alpha -ZnP2 by tuning thermally the absorption edge through the 632.8 nm line of a He-Ne laser. The observed cancellation of scattering cross section has been discussed by a destructive interference between the resonant and the non-resonant transitions near the indirect band edge.

Resonant Brillouin Scattering in GaSe and GaS

Resonant Brillouin scattering in the layer-type semiconductors GaSe and GaS by the pure-transverse phonons has been investigated at room temperature by using the amplified acoustical-domain injection method. The measured spectral dependence of the Brillouin-scattering cross sections has shown a weak resonant cancellation for both GaSe and GaS in the region of the fundamental absorption edges. The data have shown a good agreement with the theoretical analyses based on the quasistatic approximation and Loudon's light-scattering theory. The resonant cancellation has been successfully interpreted by taking into account the lowest-direct-gap (direct-exciton) resonance process for GaSe and lowest-indirect-gap resonance process for GaS. These analyses have also indicated that the nonresonant electronic transition is dominant in the Brillouin-scattering process even in the region near the fundamental absorption edge.

Laser induced molecular background fluorescence in flames

Laser induced fluorescence of several flame species (C 2, CH, OH, CN) was investigated in air/C 2H 2 and N 2O/C 2H 2 flames using a N 2 laser pumped-dye laser system. In all cases, the resulting fluorescence spectrum extends over a broad wavelength range. Due to collisional energy transfer in the flame, several nonresonance fluorescence transitions are observed.