Frequency metrology on theMg3s2S1→3s4p

Abstract

We report a frequency metrology study on the Mg 3s 2 1 S → 3s4p 1 P transition near 202.5 nm. For this purpose, the fourth harmonic of the output from an injection-seeded Ti: sapphire pulsed laser is employed in a Mg atomic beam experiment with laser-induced fluorescence detection. Absolute frequency calibration with a frequency comb laser is performed on the cw seeding radiation, while the chirp-induced frequency shift between the pulsed output and the seed light is monitored on line. The resulting transition frequency for the main isotope 24 Mg is determined at 49 346.756 809͑35͒ m −1 . This value is three orders of magnitude more precise than the best value in the literature. The line positions of the other isotopes 25 Mg and 26 Mg are also measured at comparable accuracy, giving rise to very exact values for the isotopic shifts. The achieved precision for the transition frequency at the 7 ϫ 10 −10 level makes this second resonance line of Mg I an additional candidate for inclusion in many-multiplet methods, aimed at detecting a possible temporal variation of the fine-structure constant ␣ from comparison with quasar spectra. The isotopic shifts obtained are also important to correct for possible systematic shifts due to evolution of isotopic abundances, which may mimic ␣-variation effects.

Precision measurements and test of molecular theory in highly excited vibrational states of H2 (v = 11)

“…An investigation of ac-Stark effects on two-photon transitions in CO was performed by Girard et al [39]. For molecular hydrogen, various studies have been performed on the two-photon excitation in the EF-X system over the years [19,[40][41][42][43]. In the following, we present our evaluation of the ac-Stark effect in F-X (0, 11) transitions where we first discuss line shape effects.…”

“…(2), was obtained by Hannemann et al [43] for the H 2 EF 1 Σ + g −X 1 Σ + g (0, 0) band, where they reported +13(7) and +6(4) MHz per MW/cm 2 , respectively, for the Q(0) and Q(1) lines. Investigations on the E-X (0, 1) band in Ref.…”

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

“…15 The fourth harmonic, Fig. 1 Evolution of the experimental uncertainty of the adiabatic ionisation energy (circles) and the dissociation energy (triangles) of H 2 .…”

“…15,34 These measurements have relied on amplified and frequency-upconverted nanosecond laser pulses, and were limited so far to an accuracy of several MHz by frequency-chirping effects, which will be difficult to further reduce. 15 The use of long pulses (100 ns or more are possible 35 ) might be considered as an alternative though it is uncertain that a 100 kHz accuracy can be reached in this way. A careful control of ac Stark shifts and residual Doppler shifts is in any case mandatory for any experiment.…”

“…Pulses with a wavelength around 202 nm could be produced by fourth-harmonic generation of the output of a Ti:Sa frequency-comb laser in three successive BBO crystals. 15 The bandwidth of the comb would have to be carefully chosen so that only the vibrational ground state of the EF state is excited, but no higher vibrational states, because their excitation would perturb the measurement.…”