Studying the regime of complete decoupling of the bond between the electron and nuclear moments at the D (1)-line of the K-39 potassium isotope using a spectroscopic microcell

Atomic transitions of the K-39 potassium isotope in strong (up to 1 kG) longitudinal and transverse magnetic fields have been studied with a high spectral resolution. It has been shown that crossover resonances are almost absent in the saturated absorption spectrum of potassium vapors in a 30-mu m-thick microcell. This, together with the small spectral width of atomic transitions (30 MHz), allows one to use the saturated absorption spectrum for determining frequencies and probabilities of individual transitions. Among the alkali metals, potassium atoms have the smallest magnitude of the hyperfine splitting of the lower level. This allows one to observe the break of the coupling between the electronic and nuclear angular momentums at comparatively low magnetic fields B > 500 G, i.e., to implement the hyperfine Paschen-Back regime (HPB). In the HPB regime, four equidistantly positioned transitions with the same amplitude are detected in circularly polarized light (sigma(+)). In linearly polarized light (pi) at the transverse orientation of the magnetic field, the spectrum consists of eight lines which are grouped in two groups each of which consists of four lines. Each group has a special distinguished G-transition and the transition that is forbidden in the zero magnetic field. In the HPB regime, the probabilities of transitions in a group and derivatives of their frequency shifts with respect to the magnetic field asymptotically tend to magnitudes that are typical for the aforesaid distinguished G-transition. Some practical applications for the used microcell are mentioned.