N. van Schaik

Depopulation effects in fluorescence experiments with a dye laser

Abstract The effect of depopulation via optical pumping with a dye laser has been investigated for the case of 1s 5 atoms of neon. Short pulses (⩽50 μs) of 588.2-nm laser light was passed at a fixed moment through the afterglow of a periodically pulsed neon gas discharge. The intensity of induced fluorescence light during the laser pulse was recorded by means of a 100-channel analog multiscaler. The experiments were carried out in dependence on the laser intensity and the laser beam diameter. In order to explain the behaviour of the observed fluorescence light intensity a numerical model based on balance equations was set up. From comparison of the model calculations with the experimental results it appeared that: (a) the fact that the excitation of 1s 5 atoms is velocity-selective on account of the mode structure of the laser light, delays the depletion of the total 1s 5 atom density appreciably, and (b) owing to diffusion of 1s 5 atoms into the path of the laser beam, a constant fluorescence signal is maintained during stationary laser irradiation. In certain conditions this fluorescence signal is still a good measure of the 1s 5 atom density which would exist if the laser irradiation were absent.

Isotope shift of the D-Lines of 20Na

Abstract The isotope shift of the 20Na D-lines relative to the 23Na D lines has been determined by means of a narrow band dye laser. The 20Na isotope is produced via the reaction 20Ne(p,n)20Na, by irradiation of neon gas with 20-MeV protons. By scanning the absorption profiles of 20Na and 23Na simultaneously by means of the laser frequency, while measuring the fluorescence light intensity, the isotope shift is found from the mutual position of both profiles. We have found Δυsh = (1800 ± 180) MHz.

Electron density and electron temperature in a neon plasma generated by 20-MeV protons

Abstract The electron density and the electron temperature in a plasma, produced by irradiation of a neon gas with a beam of 20-MeV protons, has been studied. Various neon densities in the range from 1.5×10 23 m -3 to 6.3×10 24 m -3 and proton beam currents from 3 nA to 6 μA have been taken. By repeatedly pulsing the proton beam, such conditions were set up that the electron density was determined from the time dependence of the intensity of recombination-induced line radiation during the afterglow. From the relevant measurements it followed that the total cross-section for primary and secondary ionization of neon by 20-MeV protons is (1.7±0.3)×10 -21 m 2 . By comparing the observed time dependence of recombination-induced line radiation with the results obtained from a numerical model it could be concluded that the electron temperature in a plasma produced by a continuous proton beam of 6 μA in neon of density 6.3×10 24 m -3 , be three times as high as the gas temperature (room temperature). This could be ascribed to the energy transfer of fast secondary electrons to the bulk electrons in the plasma. Finally, the relative production in the plasma of 1s states and the relative population of 2p states obtained by the dissociative recombination process is measured for neon of density 3.7×10 24 m -3 at room temperature.

Transfer of excitation between 2p levels of neon induced by collisions with neutral neon atoms

Abstract The reaction coefficients for transfer of excitation between 2p atoms of neon induced by collisions with neutral neon atoms have been determined for nine 2p states. By means of a continuous dye laser 1s atoms of neon in a plasma generated by a 20-MeV proton beam in 110 torr neon, were excited to a specific 2p state. The relative population density of 2p states produced via collisional transfer of excitation was determined from the spectrum of the induced fluorescence light. This has been carried out for laser excitation to eight 2p levels. The reaction coefficients were calculated after inserting the observed population densities in a set of balance equations. The ratios of the experimental values of the reaction coefficients for collisional coupling between each two 2p states appeared to be consistent with a relation following from the principle of detailed balancing.

Profiles of the absorption D-lines of sodium in neon observed with a single-mode dye laser

Abstract A study of the shape of the D-lines of sodium vapour in neon gas of 10 24 m -3 density, using a c.w. tunable dye laser is describedl. The line shapes have been measured by recording the flurescence signal while scanning the absorption lines with the laser frequency. The line shapes have been studied with dependence on laser intensity. For intensities lower than 0.2μ W mm -2 the shapes are equal to the sum of the Doppler-broadened hyperfine components. At larger intensities a narrowing of the line shape is observed. The shapes remain constant for laser intensities larger than 15μ W mm -2 . The narrowing effects are explained from selective depetion of the hyperfine levels of the sodium state by laser excitation.

The HF-Phase Measuring Equipment of the Eindhoven AVF-Cyclotron

For the HF-phase measurements a sampling system is used since several years. The sampling system transforms the HF-beam signals to low frequencies. Then relatively simple correlation techniques are applied. In this way noise background is suppressed and HF-phases of beams with currents as low as 60 nA are measured accurately.