A. Dönszelmann

Hyperfine structure and isotope shift measurements in neutral gallium and indium with a pulsed dye laser

Abstract An atomic beam irradiated by a narrow band dye laser is used to observe resonance fluorescence in free gallium and indium atoms. The dye laser is pumped by means of a N 2 -laser and it can be tuned to scan the various line components. From the resonance frequencies, values are derived for the hyperfine splittings of the 5s 2 S 1 2 state in 69 Ga: 2137.7 ± 2.0 MHz, and 71 Ga: 2716.0 ± 3.0 MHz, as well as the 6s 2 S 1 2 state in 115 In: 8426.0 ± 3.0 MHz, and 113 In: 8409.0 ± 4.0 MHz. The analysis of the observed frequencies also yields the isotope shifts in the resonance lines, which are 32.8 ± 3.5 MHz for Ga λ = 403.3 nm, 39.6 ± 3.5 MHz for Ga λ = 417.2 nm and 258.2 ± 3.0 MHz for In λ = 410.2 nm (the second In line is beyond the region of observation). The lines of 71 Ga and 113 In are shifted to the red. The results are compared with literature values. Experimental details of the laser set-up and the technique of observation are described.

Hyperfine structure and lifetime measurements of the 6p 2P32, 12 fine structure levels of gallium 69 and 71

Abstract We have determined the natural lifetime and hyperfine structure of the 6p 2P 3 2 and 6p 2P 1 2 levels of 69Ga and 71Ga. The levels were populated in an atomic beam apparatus by means of stepwise excitation using two pulsed dye lasers. The lifetimes, deduced from the fluorescence decay, are 160 ± 35 ns for the 2P 1 2 level and 150 ± 15 ns for the 2P 1 2 level. The hyperfine structure splittings were determined by means of the quantum beat method. The A factor found for 6p 2P 1 2 is 53.3 ± 0.7 MHz for 69Ga and 67.4 ± 0.7 MHz for 71Ga. The A and B factors of 6p 2P 3 2 are for 69Ga 22.4 ± 0.2 MHz and 3.2 ± 0.3 MHz, respectively, and for 71Ga 28.5 ± 0.2 MHz and 2.4 ± 0.3 MHz, respectively. The positive sign of all hfs constants, which cannot be deduced from the quantum beat measurements, is taken from the results of Hartree-Fock calculations.

Recording and averaging transients with high repetition rates

Describes the modification of a Tektronix transient digitiser, which allows recording and averaging of transient signals with a minimum duration of 1 ns and a repetition frequency of 50 Hz. The possibility of higher repetition rates is discussed.

Dye laser study of the np 2P12,32 Rydberg series in neutral gallium and indium atoms

We investigated the np 2P12,32 Rydberg series in indium and gallium. The high levels were populated in an atomic beam apparatus using stepwise excitation with two pulsed dye lasers. The series turn out to be unperturbed and the level values are described with high precision by extended Rydberg-Ritz formulae. From the accurate level values we determined the ionization limit of indium at 46 670.106±0.006 cm-1, and the ionization limit of gallium at 48 387.634±0.010 cm-1. The result for indium is in perfect agreement with earlier values derived from other Rydberg series. The fine structure splitting of the Rydberg states in gallium was resolved for the first time. The splitting is proportional to n∗-3 over the range observed, just as in indium. Anomalies found for the fine structure intensity ratio in the transitions of both indium and gallium are discussed. From the measurements in gallium we have derived isotope shifts relative to the ionization limit for the 5s 2S12 state, 7±4 mK, and the 4p 2P12 and 2P32 levels, 6±4 mK (1 mK is 0.001 cm-1).

Configuration interaction effects in the 4s2nd 2D32, 52 Rydberg series of neutral gallium investigated with pulsed dye lasers

Abstract We investigated the perturbation of the 4 s 2 n d 2 D 3 2 , 5 2 Rydberg series in gallium due to configuration interaction with the 2 D term of the 4s4p 2 configuration. The high 2 D levels were populated by stepwise excitation using 5s 2 S 1 2 as the intermediate state. The atoms were excited in an atomic beam apparatus by two pulsed dye lasers. We determined the position of the series members accurately from the forbidden 5s 2 S 1 2 - n d 2 D 3 2 , 5 2 transitions (19 ⩽ n ⩽ 34). The transition probability of these forbidden lines was strongly increased by applying a weak electric field during the excitation. The scalar polarizability of the d levels was measured too. The Rydberg atoms were detected by means of the field ionization technique. The fine structure splitting of the high d levels has been resolved for the first time. The splitting is not proportional to n ∗−3 over the range of observation and is enlarged dramatically by the perturbation. A description of the effects is presented in the framework of perturbation theory with Hartree-Fock values as a first-order approximation. Level values for the autoionizing 4s4p 2 2 D 3 2 , 5 2 levels are predicted and compared with observations.

A study of the np 2P12,32 Rydberg series in neutral indium by means of two-photon laser spectroscopy

Abstract The 5p 2P 3 2 −np 2P 1 2 , 3 2 two-photon transitions in neutral indium, with 25 ⩽ n ⩽ 43, have been studied by using a pulsed dye laser. The fine structure of the upper levels has been resolved for the first time and shows a hydrogenic behaviour over the series. The accurately determined quantum defects confirm the value of the ionization limit, 46670.107 cm-1, derived previously from the 2S series. Discrepancies between our results and those obtained in earlier investigations are discussed. The relation predicted by theory between the two-photon transition probability and the energy difference between the real and the virtual intermediate level has been verified experimentally.

Extension of the measurements of the np 2P12,32 and nd 2D32,52 Rydberg series in neutral indium

Abstract Stepwise excitation by means of two dye layers has been used to study the n p 2 P 1 2 , 3 2 and n d 2 D 3 2 , 5 2 Rydberg levels in indium, with 16 ⩽ n ⩽ 31. The fine structure of the 2 P series shows a hydrogenic behaviour also in this region. The fine structure splitting of the 2 D series varies as n ∗−3 for n >35 and as a linear combination of n ∗−3 and n ∗−5 for 16 ⩽ n ⩽ 35. The perturbation of the n d 2 D series, due to configuration interaction with the 5s5p 2 2 D term, is reanalysed. New values for the position of the 5s5p 2 2 D 3 2 , 5 2 levels are given.

Configuration interaction effects in the 2Sbuilt12, 2Dbuilt32,built52 rydberg series of neutral indium investigated with a frequency-doubled dye laser

Abstract The 5s 2 5p 2 P built3 2 − 5s 2 ns 2 S built1 2 , 5s 2 nd 2 D built3 2 , built5 2 Rydberg series (25 ⩽ n ⩽ 107) in indium have been investigated with high precision. The atoms were excited in an atomic beam by a frequency-doubled pulsed dye laser (λ ≈ 225 nm). The highly excited atoms were detected using the field ionization technique. The ionization limit has been determined at 46 670.107 ± 0.010 cm-1 from the 2 series. The perturbation of the series due to configuration interaction with the 2D term of the 5s5p2 configuration has been studied. Discrepancies with previous observations of these series are discussed. The fine structure splitting of the 2D levels could be determined up to n 2D up to n = 70. It is found to be almost proportional to n ∗-3 over the range observed, but the size of the splitting is strongly affected by the perturbation. A description of the effects is presented in the framework of perturbation theory with Hartree-Fock values as a first order approximation. Level values for the 5 s 5 p 2 2 D built3 2 , built5 2 levels are predicted and compared with observations.

Investigation of the 4s4p2 configuration in gallium

Abstract The region above the first ionization limit in neutral gallium is investigated using two-step laser ionization. In this region the autoionizing 2S and 2D levels of the 4s4p2 configuration are located. The lifetimes of the 4s4p2 4P levels which lie below the ionization limit, and the relative intensities of the 4s24p 2P − 4s4p2 4P transitions are determined.

Hyperfine structure and lifetime measurements of the 8p 2P32,12 levels of indium 115

Abstract The natural lifetime and hyperfine structure of the 8p 2P 1 2 and 8p 2P 3 2 levels of 115In have been determined. The levels have been populated in an atomic beam by pulsed stepwise laser excitation. The fluorescence from the excited states was observed by a fast photomultiplier. The lifetimes, deduced from the fluorescence decay are 316 ± 20 ns for the 2P 3 2 level and 312 ± 20 ns for the 2P 1 2 level. The hyperfine structure splittings were determined by means of quantum beats. The A-factor found for the 2P 1 2 level is 44.2 ± 0.4 Mhz. The A and B factor deduced from the hyperfine splittings of the 2P 3 2 level are 16.3 ± 0.1 MHz and 11.4 ± 0.3 MHz, respectively.