A study of hyperfine transitions of singly ionized praseodymium (141Pr+) using collinear laser ion beam spectroscopy

This paper presents the general spatial Schmidt decomposition of two-photon fields generated in spontaneous parametric down-conversion (SPDC). It discusses in particular the separation of the radial and azimuthal degrees of freedom, the role of projection in modal analysis, and the benefits of collinear phase mismatch. The paper is written in a review style and presents a wealth of numerical results. It aims at emphasising the physics beyond the mathematics, through discussions and graphical representations of key results. The two main conclusions of the paper are the finding of a better law to describe the effective dimensionality of the spatial part of the total Hilbert space and a possible novel feature of the radial Schmidt modes.     

Modelling of emission spectra of Pr I by summarizing hyperfine patterns of overlapping spectral lines

We present studies of the the hyperfine (hf) structure of spectral lines of Praseodymium (Pr) by laser spectroscopic investigations as well as by analyzing Fourier Transform (FT) spectra. The experimental part of our work is done with the technique of laser-induced fluorescence (LIF) spectroscopy in a hollow cathode lamp. We present detailed studies of the very small region of 1.5 Å (from 5810.5 Å to 5812.0 Å) in the visible area of the FT spectrum where at least 14 spectral lines are overlapping. In the investigated region we discovered two new even levels and three new odd levels and could classify 11 new spectral lines. The final goal is to model the emission spectrum by a sum of the hf profiles of all spectral lines in a certain region. Application of such modelling may be found in analyzing highly resolved stellar spectra.     

Investigation of mass and energy coupling between soot particles and gas species in modelling ethylene counterflow diffusion flames

A numerical model is developed aiming at investigating soot formation in ethylene counterflow diffusion flames. The mass and energy coupling between soot solid particles and gas-phase species is investigated in detail. A semi-empirical two-equation model is chosen for predicting soot mass fraction and number density. The model describes particle nucleation, surface growth, and oxidation. A detailed kinetic mechanism is considered for the gas phase and the effect of considering radiation heat losses is also evaluated. Simulations were done for a range of conditions that produce low-to-significant amounts of soot using three strategies: first by changing the strain rate imposed on the flow field, second, by changing the oxygen content in the oxidant stream, and third, by changing the pressure. Additionally, the effect of the transport model chosen was analysed. The results showed that, for the flames studied and within the limits of the present work, the soot and gas radiation terms are of primary importance for numerical simulations. Additionally, it was shown that the soot mass and thermodynamic properties coupling terms are, in general, a second-order effect, with an importance that increases as soot amount increases. As a general recommendation, the radiation terms have always to be considered, whereas full coupling has to be employed only when the soot mass fraction, Y_S, is equal to or larger than 0.008. If a higher precision is required, with errors less than 1%, full coupling should be taken into account for Y_S ≥ 0.002. For lower soot amounts, the coupling through soot mass and thermodynamic properties may be neglected as a first approximation, but an error on the total mass conservation will be present. Additionally, discrepancies from considering different transport models (detailed or simplified) are larger than those found from not fully coupling the phases.     

Phase measurements of ring dark solitons

A four-frame technique for interferogram analysis is used to measure the transverse phase distribution of nonlinearly split 2D dark beams. Pairs of diametrical phase shifts within each ring are retrieved from the experiment. This result is one of the tests required to denote the formations observed as ring dark solitons.     

Zeeman- and Paschen-Back-effect of the hyperfine structure of the sodiumD 1-line

Using high-resolution laser-atomic-beam spectroscopy, Zeeman- and Paschen-Back-effects of the hyperfine structure of the sodium resonance lines were studied in fields up to app. 280 G. The results derived for theD ₁-line are given in graphical form and show clearly the change in the coupling ofJ andI of the upper level.     

Semiclasical model of magneto-optical trap depth

We report the results of trap depth calculations based on the semiclassical theory of interaction of light field with atom in magneto-optical trap (MOT). In our model of magneto-optical trap we take into account Zeeman shift of ground and excited states in local magnetic field and only Doppler cooling force are considered. The calculated trap depth has been compared with value of trap depth estimated from experimental results for ⁷Li.     

Measurement of the transition wavelengths of the lithium resonance lines

Using laser-atomic-beam spectroscopy and a highly precise lambdameter, we have determined the transition wavelengths of the lithium resonance lines to be:⁶Li D₁: 6707.0704(5)Å,⁶Li D₂: 6707.9195(5)Å;⁷Li D₁: 6707.9241(5)Å,⁷Li D₂: 6707.7723(5)Å at spectroscopic conditions (15 °C, 760 mm Hg).     

Hyperfine structure investigations of the tantalumI blend λ=6356.14 Å

The TaI line 6356.14 Å, up to now classified as the transition 5d ³6s ² a ⁴ P _5/2?5d ³6s(a ⁵ F)6p z ⁴ F ₇ ^2/0 , is a blend with a second transition, which is related to the additional levels 5d ⁴(b ³ G)6s a ⁴ G _9/2?39641.24 cm^?1 J=7/2°. Using laser excitation with optogalvanic and laser-induced fluorescence detection, the hyperfine constants of the four levels involved and the distance of the center wavelengths of the two fine structure transitions could be determined.     

The sodium D2-line in crossed electric and magnetic fields

The influence of perpendicularly crossed electric and magnetic fields on the sodium D₂-line was studied using laser-atomic-beam spectroscopy. The observed spectra show changes in the polarization type when one of the fields becomes dominant relative to the other.