  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.
