Laurentius Windholz

ULTRA-VIOLET-LASER-INDUCED CHEMILUMINESCENCE OF NACD AND NAHG EXCIMERS

A single line UV Ar++ laser has been used for the photochemical production of NaCd and NaHg excimers, detected by their characteristic bound–free emission in the blue spectral region. Selected laser lines excited specific levels in the C 1Πu electronic state of the Na2 molecule. The chemical reaction of the excited sodium dimer with Cd or Hg atoms produced NaCd and NaHg excimers. We suggest a simple model for the explanation of the observed spectra, based on recent ab initio theoretical calculations.

Observation of Phase-Dependent Coherent Population Trapping in Optically Closed Atomic Systems

Phase-dependent coherent population trapping (CPT) was observed using a thermal Na atomic beam irradiated by four laser fields derived from two dye lasers. Investigations were made on Λ- and double Λ-systems created in the D1 line, both with and without magnetic field that lifts degeneracy of the Zeeman sublevels. In all cases a sharp decrease of fluorescence intensity was observed for certain values of the relative phase of the light waves, indicating that the occurrence of CPT depends on this phase. The shape of the phase dependence as well as its behaviour with respect to laser intensity fits well theoretical predictions.

Investigation of the hyperfine structure of Pr I and Pr II lines based on highly resolved Fourier transform spectra

We report the recording of new highly resolved Fourier transform spectra of the neutral praseodymium atom. With the help of the new spectra we found about 9000 new lines from which—in the region 3260 to 9880 A—1194 could be classified as transitions between energy levels of the Pr atom and 19 as transitions of the Pr ion. Twenty-three new atomic energy levels of odd parity and one of even parity were discovered during this first examination. The spectra might be very helpful for further laser spectroscopic investigations of the hyperfine structure of Pr I and Pr II transitions.

Re-measurement of the transition frequencies, fine structure splitting and isotope shift of the resonance lines of lithium, sodium and potassium

Performing laser-atomic beam spectroscopy, we have remeasured the transition frequencies and the fine structure splitting of the lithium, sodium and potassium resonance lines. Additionally, the isotope shifts6Li-7Li could be determined with high accuracy. Transition frequencies were determined by means of a high-precision lambdameter working at vacuum conditions, calibrated by saturation absorption of127I2. Frequency differences up to 1 THz could be determined with the help of a carefully calibrated marker etalon with systematical errors smaller than 1 MHz.

Polarization-dependent sensitivity of level-crossing, coherent-population-trapping resonances to stray magnetic fields

Coherent-population-trapping resonances within the degenerate two-level system of the F=2-->F′=1 transition of the 87Rb D1 line were investigated in an uncoated Rb vapor cell by means of level-crossing-type experiments. Tuning over the two-photon resonance is achieved sweeping a magnetic field around zero value. The influence of transverse magnetic fields on the amplitude and the width of the resonances, recorded in fluorescence and absorption, were investigated in the cases of excitation with linear, circular, and elliptical laser light polarization. A theoretical analysis was performed for the case of linearly polarized excitation, the results of which are in good agreement with the experiment.

New energy levels and hyperfine structure measurements of neutral lanthanum by laser-induced fluorescence spectroscopy

This study is focused on the search for new energy levels and the classification of weak spectral lines by analysing hyperfine (hf) spectra. Laser-induced fluorescence spectroscopy as well as optogalvanic spectroscopy were applied to measure the hf structure of Lanthanum transitions. Free La atoms are produced and excited in a hollow-cathode discharge. Ninety-six spectral lines have been analysed in the spectral range from 430 to 742 nm using a tunable single-mode cw dye laser operating with different dyes. Ninety-four of these lines are new, which means they are not listed in commonly used wavelength tables. A classification program was used to classify these 94 lines. Eighteen new energy levels were discovered. They were confirmed by further laser excitation. Fifty-one other spectral lines were classified via their hf pattern and centre-of-gravity wavenumber from Fourier transform spectra in order to prove the new even energy levels. In addition, 31 spectral lines were observed and classified as fluorescence transitions from the excited upper levels. A total of 176 spectral lines could be classified in this work. Seventy-three magnetic dipole hf structure constants A for the upper energy levels of the transitions were determined and compared with references, if available. Twenty-three of these constants are measured for the first time (including the A constants for 18 new levels).

Investigation of the hyperfine structure of lanthanum lines by a laser-induced fluorescence technique

Hyperfine constants of lanthanum I and II levels are reported, determined using laser excitation and fluorescence detection. Free La atoms and ions were produced in a hollow cathode discharge and excited using laser light, generated by a tunable ring dye laser, working with the dyes Coumarin 102, Coumarin 30 and Rhodamine 700. More than 150 spectral lines are investigated for the determination of the magnetic dipole coupling constants A and the electric quadrupole coupling constants B of 99 levels of La I and 28 levels of La II. The constants A and B for seven known levels of La I are reported for the first time in this work. Four new levels of La I are also discovered and confirmed by a second laser excitation.

Optogalvanic spectroscopy of the hyperfine structure of weak La I lines: discovery of new even parity fine structure levels

The hyperfine structure of weak La I lines was experimentally investigated using laser optogalvanic spectroscopy in a hollow cathode discharge lamp. More than 100 La I lines were investigated and 40 new energy levels were discovered, most of them having even parity. The magnetic hyperfine interaction constants A and in some cases the electric quadrupole interaction constants B for these levels were determined. All the newly discovered levels were confirmed either by additional laser excitations (from other known levels) or by lines in a Fourier transform spectrum which could now be classified.

Efficient Raman sideband generation in a coherent atomic medium

We demonstrate the efficient generation of Raman sidebands in a medium coherently prepared in a dark state by continuous-wave low-intensity laser radiation. Our experiment is performed in sodium vapor excited in

Optical measurement of the free spectral range and spacing of plane and confocal Fabry-Perot interferometers

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