Related papers: Measurement of the $2$S$_{1/2}-8$D$_{5/2}$ transit…
We present absolute frequency measurements of 2S_{1/2}-nS_{1/2} two-photon transitions with n = 8, 9, and 10 in a cryogenic beam of atomic hydrogen. Each transition has been measured with a fractional uncertainty of approximately…
We present a new measurement of the $1S-3S$ two-photon transition frequency of hydrogen, realized with a continuous-wave excitation laser at 205 nm on a room-temperature atomic beam, with a relative uncertainty of $9\times10^{-13}$. The…
The measurement by Pohl et al. [1] of the 2S_1/2^F=1 to 2P_3/2^F=2 transition in muonic hydrogen and the subsequent analysis has led to a conclusion that the rms charge radius of the proton differs from the accepted (CODATA [2]) value by…
Using the Dirac equation, radiative corrections and finite nuclear size and mass corrections, we calculate the $1s$-$2s$ quantum transition frequency $f_{1s,2s}$ of hydrogen and its uncertainty due to the uncertainties $\delta m_e, \delta…
We have measured the 1S - 2S transition frequency in atomic hydrogen via two photon spectroscopy on a 5.8 K atomic beam. We obtain $f_{1S-2S} = 2 466 061 413 187 035 (10)$ Hz for the hyperfine centroid. This is a fractional frequency…
The proton radius puzzle is known as the discrepancy of the proton radius, obtained from muonic hydrogen spectroscopy (obtained as being roughly equal to 0.84fm), and the proton radius obtained from (ordinary) hydrogen spectroscopy where a…
The nonresonant (NR) corrections are estimated for the most accurately measured two-photon transition 1s-2s in the hydrogen atom. These corrections depend on the measurement process and set a limit for the accuracy of atomic frequency…
The "proton radius puzzle" was recently solved by reducing the four-standard deviation discrepancy between the results for electronic hydrogen ($H$) and muonic hydrogen ($\mu H$) atoms to $3.3$ value. The value of the root-mean-square…
This article reports the first optical frequency measurement of the $1\mathrm{S}-3\mathrm{S}$ transition in hydrogen. The excitation of this transition occurs at a wavelength of 205 nm which is obtained with two frequency doubling stages of…
High resolution spectroscopy of the hydrogen atom takes on particular importance in the new SI, as it allows to accurately determine fundamental constants, such as the Rydberg constant and the proton charge radius. Recently, the second most…
An optical measurement of the 2S hyperfine interval in atomic hydrogen using two-photon spectroscopy of the 1S-2S transition gives a value of 177 556 834.3(6.7) Hz. The uncertainty is 2.4 times smaller than achieved by our group in 2003 and…
In 2003 we have measured the absolute frequency of the $(1S, F=1, m_F=\pm 1) \leftrightarrow (2S, F'=1, m_F'=\pm 1)$ two-photon transition in atomic hydrogen. We observed a variation of $(-29\pm 57)$ Hz over a 44 months interval separating…
A measurement of the Lamb shift of 49,881.88(76) GHz in muonic hydrogen in conjunction with theoretical estimates of the proton structure effects was recently used to deduce an accurate but rather small radius of the proton. Such an…
We have remeasured the absolute $1S$-$2S$ transition frequency $\nu_{\rm {H}}$ in atomic hydrogen. A comparison with the result of the previous measurement performed in 1999 sets a limit of $(-29\pm 57)$ Hz for the drift of $\nu_{\rm {H}}$…
The principal limits for the accuracy of the resonance frequency measurements set by the asymmetry of the natural resonance line shape are studied and applied to the recent accurate frequency measurements in the two-photon 1s-2s resonance…
We present the first precise frequency measurement of the 2$^{1}$S$_{0}$-3$^{1}$D$_{2}$ two-photon transition in $^{4}$He at 1009 nm. The laser source at 1009 nm is stabilized on an optical frequency comb to perform the absolute frequency…
The measurement of the 2P^{F=2}_{3/2} to 2S^{F=1}_{1/2} transition in muonic hydrogen by Pohl et al. and subsequent analysis has led to the conclusion that the rms radius of the proton differs from the accepted (CODATA) value by…
We study the 1S-3S two-photon transition of hydrogen in a thermal atomic beam, using a homemade cw laser source at 205 nm. The experimental method is described, leading in 2017 to the measurement of the 1S-3S transition frequency in…
We demonstrate a technique for frequency measurements of atomic transitions with a precision of 30 kHz. The frequency is measured using a ring-cavity resonator whose length is calibrated against a reference laser locked to the $D_2$ line of…
We have observed the cold collision frequency shift of the 1S-2S transition in trapped spin-polarized atomic hydrogen. We find $\Delta \nu_{1S-2S} = -3.8(8)\times 10^{-10} n Hz cm^3$, where $n$ is the sample density. From this we derive the…