H T Duong

High-resolution laser spectroscopy on the D1 and D2 lines of 39,40,441K using RF modulated laser light

Two natural polyisotopic potassium beams were illuminated respectively by a RF modulated and an unmodulated laser beam. The laser side band frequency is locked on an atomic frequency, while the unmodulated laser frequency is RF scanned. The RF accuracy of the frequency scale allows measurements to about 0.3 MHz of the hyperfine structures and the isotope shifts of the D1 and D2 lines of 39,40,41K. The results obtained are reported and compared to the previous ones.

Field ionisation study of high lying Rydberg states of Na

The authors describe the details of an experiment using a sodium atomic beam and two dye lasers. By stepwise excitation they have selectively populated highly excited ns, nd and, using Stark mixing, np states fron n=20-50. The excited atoms were detected by field ionisation. The results obtained for the ionisation threshold fields for these states are presented and compared with the theoretical classical law Fc=(2n*)-4. A suitable field shape and detection technique allows the observation of multiple thresholds with high sensitivity. Multiple thresholds for nd states have been observed, as expected. Some ns singlet states also show multiple thresholds. Using suitably polarised laser beams the mod mL mod dependence of the ionisation threshold fields for the 20d state has been observed. The approach proposed recently by Gallagher for predicting the threshold fields is generally confirmed.

Experimental separation and study of the two partial photoionisation cross sections σ3p,s and σ3p,d from the 3p state of sodium

The two partial photoionisation cross sections sigma 3p,s and sigma 3p,d from the 3p state of Na were measured separately using an atomic beam of sodium and two appropriately polarised light sources. The observed variations of the two partial cross sections with the wavenumber of the photoionising light in the range 24000-29000 cm-1 above threshold are compared with earlier theoretical results.

Energies of some triplet levels in 4He I

The authors have used saturated absorption spectroscopy and a sigmameter to obtain the absolute wavelengths of the 2p 3P0,1,2-3d 3D1,2,3 transitions near 587.6 nm in 4He I. The precision is about eight parts in 109. By comparing with recent two-photon measurements of direct excitation from the 2s 3S1 level, they obtain values for the wavelengths of the 2s 3S1-2p 3P0,1,2 transitions. Precision calculations for these transitions are compared with experiment. In particular, the authors discuss the QED and relativistic corrections. The relative energies of many triplet levels in He I are analysed.