LAUSR

The selective reflection of laser radiation from the interface between a dielectric window and the atomic vapors confined in a nanocell of thickness L ≈ 350 nm is used to develop effective Doppler-broadening- free spectroscopy of potassium atoms. A small atomic line width and a relation between the signal intensity and the transition probability allowed us to resolve four lines of atomic transitions responsible for the D1 lines of the 39K and 41K isotopes. Two groups containing four atomic transitions form in an applied magnetic field upon pumping by radiation with circular polarization σ+ or σ–. Different intensities (probabilities) of transitions for the σ+ and σ– excitations are detected in magnetic field B0 ≈ Ahfs/μB ≈ 165 G (Ahfs is the magnetic dipole constant for the ground state and μB is the Bohr magneton). A substantially different situation is observed at B ≫ B0, since high symmetry appears for the two groups formed by radiation with circular polarization σ+ or σ–. Each group is the mirror image of the other group with respect to the frequency of the 42S1/2–42P1/2 transition, which additionally proves the occurrence of the complete Paschen–Back regime of the hyperfine structure at B ≈ 2.5 kG. A developed theoretical model well reproduces the experimental results. Possible practical applications are described. The results obtained can also be applied to the D1 lines of 87Rb and 23Na.