Selective Reflection of Potassium Vapor Nanolayers in a Magnetic Field

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 39 K and 41 K 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 B 0 ≈ A hfs /μ B ≈ 165 G ( A hfs is the magnetic dipole constant for the ground state and μ B is the Bohr magneton). A substantially different situation is observed at B ≫ B 0 , 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 4 2 S 1/2 –4 2 P 1/2 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 D 1 lines of 87 Rb and 23 Na.