The final result of a 2s Szy2 -2p Pzy2 Lamb-shift measurement by the laser resonance method in hydrogenic phosphorus is reported. Metastable 2s Sigz ions were prepared using a P 0.08 velocity beam of P + ions obtained from the MP tandem accelerator at the Centre de Recherches Nucleaires in Strasbourg. From the metastable state the transition to the 2p P3g2 state was induced with a high-power dye laser leading to a measured transition energy of AE' = 2.23133(12) eV. Subtracting the well-known fine-structure splitting AEFs = 2.31482(2) eV, the Lamb shift is deduced to be E,"~t(LS) = 20 188 (29) GHz. This result is compared with the theoretical value Eth, ,(LS) = 20 254(10) GHz and with other experimental results for the Lamb shift in the region Z & 18. Finally, the utility of the Lamb-shift measurements in testing the G(Zcx) function of the self-energy, which includes only terms in (Zn)", n ) 6, is discussed. PACS number(s): 12.20.Fv, 32.70.3z, 32.30.r, 31.30.Jv

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For the application of autocollimation spectroscopy [Z. Phys. D 18, 249-255 (1991)] a pulsed dye laser that is emerging from a focus (diameter, 1 mm; divergence, 30 mrad) has to be reflected back in itself with high precision. The difference Δθ between the mean angles of the counterpropagating laser beams has to be less than 1 × 10(-6) rad. Using a paraxial approximation, we show that a cat's eye fulfills the needs best. An adjustment procedure together with additional calibration equipment (CCD arrays and quadrant diodes) for the device is presented. Accounting for the uncertainties of the adjustment and using ray tracing, we show that Δθ ≤ 5 × 10(-7) rad can be achieved.

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