Accurate spectroscopy of Sr atoms

We report the frequency measurement with an accuracy in the 100 kHz range of several optical transitions of atomic Sr : $^1S_0- ^3P_1$ at 689 nm, $^3P_1- ^3S_1$ at 688 nm and $^3P_0- ^3S_1$ at 679 nm. Measurements are performed with a frequency chain based on a femtosecond laser referenced to primary frequency standards. They allowed the indirect determination with a 70 kHz uncertainty of the frequency of the doubly forbidden 5s^2^1S_0- 5s5p^3P_0 transition of $^{87}$Sr at 698 nm and in a second step its direct observation. Frequency measurements are performed for $^{88}$Sr and $^{87}$Sr, allowing the determination of $^3P_0$, $^3P_1$ and $^3S_1$ isotope shifts, as well as the $^3S_1$ hyperfine constants.Comment: 12 pages, 16 figure

Sub-natural absorption resonances on the D1 line of rubidium induced by coherent population trapping

A narrow (70 kHz fwhm) high-contrast resonance formed due to coherent population trapping (Λ-resonance) has been observed in 87Rb vapour by using two independent laser diodes. The first results on the dependences of its width on magnetic field, laser intensity and divergence are reported. The Λ-resonance is used to stabilize the difference of laser frequencies to the hyperfine splitting of the Rb ground state. A new technique of stable microwave signal generation is proposed. It is based on optical locking of two lasers via Λ-resonance in a cell inserted in an external cavity of a laser diode

Intensity and concentration dependence of Doppler-free resonance in selective reflection

Influence of laser radiation intensity on the amplitude and width of the Doppler-free resonance of selective reflection in the vicinity of the 87Rb D1 line has been investigated. The shift of the selective reflection resonance with respect to the frequency of unperturbed atomic transition is found to be red and have the value of δ = (2.6 ± 0.7) MHz. It does not vary within the accuracy limit with concentration in the range of 2 x 1013-3 x 1014 cm-3 (which corresponds to the selfbroadening variation from 2 to 30 MHz) and with the 2-120 mW/cm2 intensity change. An explanation of the absence of the concentration depended shift and the dependence of reflection resonance amplitude on intensity is proposed. It is based on the consideration of the optical pumping in the hyperfine levels of the ground state