We report experimental study of resonance sign reversal at the hyperfine Fg = 4 → Fe = 5 transition on D2 line of 133Cs. Alkali vapors are confined in an optical cell with micrometric thickness. For circular polarization of the irradiating light, transmission and reflection spectra, recorded at different laser intensities and different temperature of alkali vapor, are studied and compared. At low laser intensity, in the transmission spectra we observe a narrow resonance of increased absorption (bright resonance) at the Fg = 4 → Fe = 5 transition, however in reflection spectra, recorded at the same experimental conditions, this bright resonance transforms into a dark resonance of reduced absorption. A simple explanation is proposed in order to explain the observed difference between the transmission and reflection spectra.
This paper presents a narrow linewidth, high resolution, and high quantum efficiency imaging transmission filter based on optical trapping of resonance radiation in potassium vapor. The filter can be used to image radiation over a bandwidth narrow enough to fall within a Fraunhofer dark zone in the solar spectrum, and it can be applied to the imaging of flames, plumes or discharges containing potassium. It may also be applicable to the imaging of Raman scattering from a tunable laser. The spectral and imaging properties of the filter are demonstrated with a 1 cm aperture optically thick potassium cell illuminated by a narrow linewidth tunable laser. The spectral width at the potassium D2 line wavelength, 766.5 nm, is shown to be 1 to 2 GHz (.002 nm). At the line center, the quantum efficiency is better than 60% and the imaging resolution is better than 30 line pairs per mm. By employing a 200 micron "thin" potassium vapor cell, it is also shown that the filter maintains the high quantum efficiency (~50%) and good imaging capability (~20 lines per mm) across the 2 GHz spectral bandwidth of the cell. The "thin" cell has an out-of-band rejection of better than 1000. Its operation is demonstrated with a tunable laser as well as with broad band light from a potassium lamp and from a potassium chloride seeded flame.
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.