We present the first evidence of excitation of the 5p 3/2 → 6p 1/2 electric dipole-forbidden transition in atomic rubidium. The experiments were carried out in a rubidium vapor cell using Doppler-free optical-optical double-resonance spectroscopy with counter-propagating beams. A 5s 1/2 → 5p 3/2 electric dipole preparation step using a diode laser locked to the F = 3 → 4 cyclic transition of the D2 line in 85 Rb is used to prepare the atoms in the first excited state. This is then followed by the 5p 3/2 F 2 = 4 → 6p 1/2 F 3 dipole-forbidden excitation (λ ≈ 917.5 nm) to establish a two-photon ladder (Ξ) excitation scheme. Production of atoms in the 6p 1/2 excited state is verified by detection of the 421 nm fluorescence that results from direct decay into the 5s 1/2 ground state.The polarization dependence of the relative intensities of the lines of the decay fluorescence is also investigated. Experimental data for different polarization configurations of the light beams used in this two-photon spectroscopy are compared with the results of calculations that consider a strong atom-field coupling in the preparation step, followed by a weak electric quadrupole excitation and the blue fluorescence decay emission. Good agreement between experiment and this three-step model is found in the case of linear-linear polarizations.

This work demonstrates an scheme in which a weak electric quadrupole (E2) transition with a controlled frequency detuning in a ladder configuration is used as an extremely non-perturbing probe for precisely identifying subtle details of the effects driven by AC fields coupling atomic states and the preparation of quantum states. For this purpose, we provide a precise experimental and theoretical study of the Autler Townes (AT) effect derived from a strong electric dipole transition stimulated by a resonant laser beam and probed by the E2 interaction. The experiment was carried out for a 87Rb atomic gas at room temperature in a velocity-selective scheme. The AT effect was monitored via the splitting of the fluorescence spectra associated with the spontaneous decay to the ground state. The theoretical description incorporates the modification of standard few-level schemes introduced by forbidden electric-dipole transitions selection rules. We develop an analytic ladder three-level scheme to approximate the cyclic 5S1/2 F = 2 → 5P3/2 F = 3 → 6P3/2 F = 1, 2, 3 → 5S1/2 F = 2 path. Other levels that could have effects on the fluorescence are included via a fourth level with effective parameters. Doppler effects and finite bandwidths of the laser beams are included in the theoretical model to closely reproduce the experimental results.

We present an experimental scheme that produces Doppler-free spectra of the 5s → 6p second resonance transition in atomic rubidium. The experiment uses the saturation of the cascade fluorescence that occurs when thermal rubidium atoms interact with two counterpropagating 420 nm laser beams of comparable intensity. Part of the excited atomic population goes through the 5p 3/2 level which then decays by emission of 780 nm photons. Narrow dips appear in this otherwise broad 780 nm fluorescence, which allow resolution of the 6p 3/2 hyperfine structure. A rate equation model is used to interpret the spectra. It is also shown that these narrow peaks can be used to lock the frequency of the 420 nm laser. Using a second beam modulated in frequency produces three sets of spectra with known frequency spacings that can be used to perfom an all-optical measurement of the hyperfine splittings of the 6p 3/2 manifold in rubidium.

-This paper presents the principles and application of a super-resolution (SR) technique, based on a L1-Norm minimization procedure. In particular, the technique is applied to improve low-resolution resolution spectra as obtained from the optogalvanic effect in Neon and Argon discharges over the 413-423 nm wavelength range. By applying the super-resolution algorithm to the experimental data, a surprising 70-fold reduction of the linewidth is achieved allowing to resolve prior indistinguishable peaks. It is found that further improvements on the resolution are limited by the signal to noise ratio of the original spectra. The importance of a suitable mathematical representation of the experiment and the discussion on other applications of this super-resolution technique in spectroscopy are also presented.

We study the Autler Townes (AT) effect derived from a strong electric dipole transition stimulated by a resonant laser beam and probing it by means of a weak electric quadrupole transition with a controlled frequency detuning in a ladder configuration. The experiment was carried out for a 87 Rb atomic gas at room temperature in a velocity-selective scheme. The AT effect was monitored via the splitting of the fluorescence spectra associated with the spontaneous decay to the ground state. The theoretical description incorporates the modification of standard few-level schemes introduced by forbidden electric-dipole transitions selection rules. We develop an analytic ladder threelevel scheme to approximate the cyclic 5Spath. Other levels that could have effects on the fluorescence are included via a fourth level with effective parameters. Doppler effects and finite bandwidths of the laser beams are included in the theoretical model to closely reproduce the experimental results.