Nonlinear magneto-optical resonances for systems with J~100 observed in K2 molecules

We present the results of an experimental as well as theoretical study of nonlinear magneto-optical resonances in diatomic potassium molecules in the electronic ground state with large values of the angular momentum quantum number J~100. At zero magnetic field, the absorption transitions are suppressed because of population trapping in the ground state due to Zeeman coherences between magnetic sublevels of this state along with depopulation pumping. The destruction of such coherences in an external magnetic field was used to study the resonances in this work. K2 molecules were formed in a glass cell filled with potassium metal at a temperature above 150C. The cell was placed in an oven and was located in a homogeneous magnetic field B, which was scanned from zero to 0.7 T. Q-type and R-type transitions were excited with a tunable, single-mode diode laser with central wavelength of 660 nm. Well pronounced nonlinear Hanle effect signals were observed in the intensities of the linearly polarized components of the laser-induced fluorescence (LIF) detected in the direction parallel to the (B)-field with polarization vectors parallel (I_par) and perpendicular (I_per) to the polarization vector of the exciting laser radiation, which was orthogonal to (B). The intensities of the LIF components were detected for different experimental parameters, such as laser power density and vapor temperature, in order to compare them with numerical simulations that were based on the optical Bloch equations for the density matrix. We report good agreement of our measurements with numerical simulations. Narrow, subnatural line width dark resonances in I_per(B) were detected and explained.