Lamb shift measurement in the1t1S ground state of helium

Abstract

With a phase-modulated extreme ultraviolet pulsed laser source the frequency of the 1 1 S-2 1 P transition of helium at 58 nm has been measured. The phase modulation scheme enabled measurement and reduction of frequency chirp, usually limiting pulsed precision spectroscopy. From the measured transition frequency of 5 130 495 083͑45͒ MHz, a fourfold improved value of the ground state Lamb shift of 41 224͑45͒ MHz is deduced, in good agreement with a theoretical value of 41 233͑35͒ MHz based on QED calculations up to order ␣ 5 Z 6 . From these measurements, the well-known binding energy of the 2 1 P state and the previously determined 4 He-3 He isotope shift, accurate values for the ionization energies of the helium atom follow: 198 310.6672 (15) cm Ϫ1 for 4 He and 198 301.8808(15) cm Ϫ1 for 3 He. ͓S1050-2947͑97͒05403-6͔ PACS number͑s͒: 32.30.Jc, 12.20.Fv, 42.65.Ky

Towards measuring the ionisation and dissociation energies of molecular hydrogen with sub-MHz accuracy

“…Care would have to be taken to monitor and compensate the frequency chirp and shift occurring in the amplification process, as described, e.g., in Ref. 46. One would also have to carefully quantify the pressure shifts of the high-n Rydberg states and the ac Stark shifts of these states induced by blackbody radiation.…”

Precise laser spectroscopy of antiprotonic helium at CERN’s Antiproton Decelerator

“…We measured the frequency chirp ν c by superimposing the pulsed and cw seed beams on a photodiode and measuring the heterodyne beat signal. An electro-optic modulator (EOM) was used to apply a frequency shift to the seed laser which canceled the chirp ν c [25,26]. The linewidth of the pulsed laser beam was typically around ∼ 60 MHz [4].…”

Development of precise nanosecond and picosecond dye lasers for spectroscopy of antiprotonic atoms

“…The frequency of the dye laser pulse can deviate from the seed value by several tens MHz, due to sudden changes in the refractive index of the dye during the amplification. We corrected this so-called "frequency chirp" by using an electro-optic modulator to apply a frequency shift of opposite sign to the seed laser [16,17]. …”

“…1b). The optical frequencies of these lasers were stabilized against a femtosecond frequency comb [14,15] The cw seed beam was amplified by factor ∼ 10 6 in three dye cells pumped by the above Nd:YAG laser [16]. To decrease the Fourier-limited linewidth of the pulsed dye laser, the pump beam was split into seven beams, to which incremental delays were added.…”