We report an experimental investigation of the effect of electromagnetically induced transparency (EIT) using bichromatic laser radiation and an extremely thin cell filled with pure Rb with smoothly controllable thickness
L of the atomic vapor layer in the range $\ensuremath{\sim}780--1600\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, for which
L is comparable to the laser wavelength $\ensuremath{\lambda}$ resonant with the
D2 line
(780nm). It is revealed that the transmission spectrum of the probe laser contains two sub-Doppler peaks that have different linewidths. The narrow peak corresponds to EIT, whereas the broader one results from velocity-selective optical pumping (VSOP) and repumping processes. It is demonstrated that in the case of nonzero detuning of the coupling laser, the EIT resonance and VSOP are shifted with respect to each other on the frequency scale, which makes it possible to observe a competition between the two effects (this is not possible to realize in an ordinary cell). Also, the Dicke-type coherent narrowing effect depending on the ratio $L∕\ensuremath{\lambda}$ influences the absorption spectrum of the probe laser. Formation of an EIT resonance is substantially favored for the atoms with slow normal velocity, caused by their longer interaction time with the bichromatic laser field. As a result of the predominant contribution of these atoms, the observed linewidth of the EIT resonance is only $\ensuremath{\sim}9\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, which is more than ten times narrower than the inverse window-to-window flight time. In an external magnetic field, three and five EIT resonances have been observed for the vapor thickness of $L=2\ensuremath{\lambda}$, on
87Rb and
85Rb, respectively.
For the experimental implementation of an optically pumped atomic magnetometer, the magnetic resonance signal with a narrow linewidth and a high signal-to-noise ratio (SNR) is required for achieving a high sensitivity. Using 795-nm laser as both the pumping and the probe laser, we compare the magnetic resonance signals from different rubidium atomic vapor cells and investigate the variations of magnetic resonance signals with temperature. Optimized magnetic resonance signal is achieved with a paraffin-coated rubidium atomic vapor cell. Then the 780-nm laser at rubidium D2 line is introduced as a repumping laser, and we explore the changes of linewidth and SNR of the magnetic resonance signal under different power of the pumping laser and the repumping laser. Owing to the 780-nm repumping laser beam, the signal amplitude of rubidium-85 magnetic resonance signal is improved remarkably because more rubidium-85 atoms are spin- polarized by the 795-nm pumping laser beam. At the same time, the linewidth of rubidium-85 magnetic resonance signal is roughly not broadened anymore. We realize a closed-loop optically pumped rubidium-85 atomic magnetometer with a bandwidth of ~1.2 kHz, and the sensitivity is calibrated to be ~245.5 pT/Hz1/2 only with the 795-nm pumping laser beam. Owing to the employment of the 780-nm repumping laser beam, the sensitivity is improved to be ~26.4 pT/Hz1/2 which is improved roughly by one order of magnitude. We also calibrate the measurement accuracy and deviation of a commercial fluxgate magnetometer by using the enhanced rubidium magnetic resonance signal.