Saturated Absorption Resonances Research Articles

Magnetic coherence effects in the spectroscopy of transitions between energy levels with total angular momenta J = 1/2 and J = 1 using unidirectional waves

The physical processes that form the spectra of saturated absorption resonances at atomic transitions between energy levels with angular momenta J = 1/2 and J = 1 in the field of two unidirectional linearly polarised laser waves are studied analytically and numerically. It is shown that the specific features of the resonance spectra are formed in the Λ-schemes of transitions and manifest themselves in the form of narrow coherent structures – dips due to the magnetic coherence (optical orientation) of the transition levels induced by the optical fields. In this case, the energy levels of the lower state make the main contribution, and the contribution of the transfer of magnetic coherence from the sublevels of the upper state to the lower ones in the resonance amplitude manifests itself as an additive. Conditions are found under which the nonlinear resonance is exclusively coherent. The effect of the saturating wave field on the shape of coherent resonance structures is studied.

Resonances of electromagnetic-induced transparency and electromagnetic-induced absorption at the transition with level momenta J=1/2 in unidirectional wave spectroscopy

The physical processes that form the saturated absorption resonance spectra on the atomic transition with level momenta J= 1/2 in the field of unidirectional waves of arbitrary intensities are investigated both analytically and numerically. It is shown that the narrow structures of the nonlinear resonance spectra (resonances of electromagnetic-induced transparency and absorption) and the processes forming them are determined by the direction of the light wave polarizations, degree of openness of the atomic transition, and the saturating wave intensity. The conditions under which the nonlinear resonance is exclusively coherent, due to the magnetic coherence of transition levels, are revealed.

Numerical studies of the saturated absorption resonances in a nonlinear spectroscopy of the degenerate atomic transitions

The physical processes forming the saturated absorption resonance spectra at a number of degenerate atomic transitions at their interaction with coherent optical fields and incoherent ield of spontaneous radiation of excited atoms are studied numerically. The features of behavior of nonlinear resonance spectra depending on the degree of degeneration and relaxation parametersof level transitions, character of polarizations and intensities, as well as direction of propagation of optical fields are analyzed.

Two-frequency sub-Doppler spectroscopy of the caesium D1 line in various configurations of counterpropagating laser beams

Sub-Doppler resonances in caesium vapours are studied in a laser field produced by counterpropagating two-frequency light beams with mutually orthogonal linear polarisations. The beams are in resonance with optical transitions in the D1 line, the frequency difference of the field spectral components being equal to the hyperfine ground-state splitting in the Cs atom (∼9.2 GHz). It has already been shown that in this configuration, the hypercontrast effect can be observed for sub-Doppler resonances, which makes this configuration promising for the employment in new-generation miniature optical frequency standards. In the present work, two different two-frequency configurations are compared with each other and with the single-frequency configuration widely used in practice for observing saturated absorption resonances. The parameters of nonlinear resonances are measured at various temperatures of caesium vapours and at different optical field intensities. The results of the investigations performed make it possible to find an optimal two-frequency scheme for exciting nonlinear resonances and to estimate a potential of the scheme for its applications in quantum metrology.

Study of saturated-absorption resonances on the 3P0, 1, 2 – 3D1, 2, 3 transitions of magnesium atoms in a hollow-cathode discharge cell

The saturated-absorption resonances on the 3P0, 1, 2 – 3D1, 2, 3 transitions of magnesium atoms in a hollow-cathode discharge cell are studied. The line width (FWHM) for the observed saturated-absorption resonance on the 33P0 → 33D1 transition turns out to be ∼220 MHz. Experiments are performed using a system based on a 766-nm diode laser with amplification and frequency doubling in a nonlinear BiBO crystal. The results obtained are of interest for sub-Doppler cooling on the 33P2 → 33D3 transition.

Coherent Nonlinear Resonances of Saturated Absorption at Transitions from the Ground <sup>1</sup>S<sub>0</sub> Atomic State in the Spectroscopy of Unidirectional Waves

The shapes of the saturated absorption resonances at transitions from the ground 1S0 atom state in a gas medium in the field of two unidirectional waves are investigated both analytically and numerically. It is shown for the first time that the spectra of nonlinear resonances are formed by processes in the two-and three-level V-schemes resulting from the degeneracy of the upper P transition state, are qualitatively different at the resonant transition and transitions to the more excited atom states. It is established that the physical causes for differences of these spectra are due to the different degree of branching of the radiation from the excited to the ground state (the degree of openness) of transition. The degree of openness of transition determines the amount of contributions of coherent processes to the resonance shapes both in the system of two levels (coherent population beats) and three levels (nonlinear interference effect).

Measurements of the Rydberg Transition Energies for the n1S0 State and the Ionization Potential for 40Ca Atoms

Two-photon spectroscopy has been applied to measure the Rydberg transition energies in the n1S0 state of 40Ca atoms at n = 40–120. The ionization potential determined from these experimental data is 49305.91966(4) cm−1. Using the frequency-doubled radiation and fundamental radiation from a diode laser, the frequencies of two-photon transitions to Rydberg states with the principal quantum numbers of 75 and 76 have been measured simultaneously with the frequencies of resonances of saturated absorption in a rubidium vapor cell. The chosen transition frequencies for rubidium atoms are known with high accuracy. Such frequency references make it possible to improve the accuracy of determination of the Rydberg transition energies in 40Ca atoms.

Formation of spectra of saturated-absorption resonances on closed transitions in the spectroscopy of unidirectional waves

The formation of spectra of saturated-absorption resonances on the atomic transitions with level momenta J = 0 → J = 1 and J = 1 → J = 2 are investigated, both numerically and analytically, by the method of unidirectional linearly polarised laser waves in order to determine how the transition openness (radiation branching) affects these spectra. It is shown that, along with quantitative changes, determined by the relaxation constants of levels, value of their splitting, polarisation orientation, and wave intensities, the spectra undergo qualitative changes with a change in the degree of atomic transition openness.

Polarization Phenomena in Transparency and Absorption Effects Induced by the Field of Unidirectional Waves

Physical processes that form the spectra of saturated absorption and magnetic scanning resonances on an atomic transition with level momentum J = 1 in the field of unidirectional waves of arbitrary intensity under variation in their polarization directions are investigated by numerical simulation and analytically. It is shown that anomalies in nonlinear resonance spectra are determined by the polarization of the waves and the degree of openness of the atomic transition, while anomalies in the experimentally observed magnetic scanning spectra are attributed to the magnetic coherence induced by the fields directly on the levels of the lower state, rather than to its transfer from the excited states, as was assumed earlier.

Optimization of Stabilization Modes of Optical Frequency Standards Based on the Saturated Absorption Resonance

A theoretical study is carried out within the framework of density matrix formalism of the error signal slope for frequency standards based on the resonance of saturated absorption excited in the field of two counterwaves. Two schemes of error-signal formation are considered: in the first case, the frequency of only the test field is modulated, and, in the second case, the frequency modulation of both waves is carried out. On the basis of the calculations, the optimal parameters of harmonic modulation are determined, at which the slope has the maximum value.

Erratum to: “The influence of higher spatial harmonics of atomic polarization on the saturated absorption resonance upon excitation of open dipole transitions by a field of counterpropagating waves”

Erratum to: “The influence of higher spatial harmonics of atomic polarization on the saturated absorption resonance upon excitation of open dipole transitions by a field of counterpropagating waves”

The influence of higher spatial harmonics of atomic polarization on the saturated absorption resonance upon excitation of open dipole transitions by a field of counterpropagating waves

The effect of a double structure of saturated absorption resonance in the field of counterpropagating light waves interacting with an atomic gas is studied. The experimental observation of this effect was first reported in 2011 in a work by our colleagues at the P.N. Lebedev Physical Institute of the Russian Academy of Sciences (Laboratory of Frequency Standards). The essence of the effect lies in the fact that, on exciting an open dipole transition, another, narrower, resonance of an opposite sign can be observed at the center of the ordinary saturated absorption resonance. A theoretical analysis of this effect has also been performed in this work in terms of a simple spectroscopic model of an atom with two nondegenerate energy levels without taking into account higher spatial harmonics of atomic polarization and polarizations of light waves (scalar model). The present work is devoted to the development of a theory of the formation of a central narrow resonance for the example of a real Fg = 1 → Fe = 1 atomic transition and to the study of its main characteristics (amplitude, width, contrast, and amplitude-to-width ratio). In addition, the theoretical results obtained without taking into account the influence of higher spatial harmonics and with inclusion of the influence of first higher harmonics are compared. This comparison shows that their influence on the parameters of the new nonlinear resonance is strong even in moderately intense light fields (R ~ γ, where R is the Rabi frequency). The results of this study can be of interest for quantum metrology, as well as for many experiments in which the laser-radiation frequency is stabilized by the saturated absorption resonance on open dipole transitions in atoms and molecules.

Yb:YAG/I2 optical frequency standard at 515 nm with instability at the level 10–15

We present the results of development of an optical frequency standard based on Yb:YAG laser with second harmonic at 515 nm. The laser frequency is locked to the saturated-absorption resonance in a gas cell filled with molecular iodine. Final instability of the standard is 1.3×10–15 at 104 s.

New polarisation effects in saturated absorption spectroscopy in the field of counterpropagating light waves∗∗Reported at The Fifth Russia – China Workshop on Laser Physics and Photonics (RCWLP&P, Novosibirsk, 26 – 30 August 2015).

The effect of a double structure of saturated absorption resonance in the field of counterpropagating light waves interacting with atomic gas is considered, which was first studied experimentally and theoretically by Vasil'ev et al. [V.V. Vasil'ev et al., J. Exp. Theor. Phys., 112, 770 (2011)]. The effect manifests itself as a new nonlinear resonance formed as a peak in the absorption spectrum of the probe wave. The resonance is observed inside a ‘conventional’ dip in the spectrum of saturated absorption. Previously, this effect was theoretically described only in the frameworks of the two-level atomic model, i.e., without making allowance for degeneracy of atomic energy levels with respect to the projection of the total angular momentum and for the vector nature of light. We extend the theory of the effect to the case of real atomic systems with degenerate energy levels and arbitrary polarisations of light waves. In particular, on an example of the simple transition we show that polarisation parameters of light waves may significantly affect the contrast of the new effect and the possibility of observing it at all. Conclusions of the work are confirmed both analytically and bnumerically.

Relative amplitudes of external satellites of superfine-structure multiplets in the saturated absorption spectrum of SiF4

Variation of amplitudes of Doppler-free saturated absorption resonances as a result of changes in the gas pressure and power of light waves is studied theoretically and experimentally. The results of the investigation are used for the interpretation of weak satellites of superfine-structure multiplets in the spectrum related to tunnel transitions between energy states of a molecule corresponding to its rotation about equivalent symmetry axes. Relative amplitudes of satellites of the AFE and FEF multiplets of the superfine structure of the SiF4 molecule in the frequency tuning interval of a CO2 laser operating at the P(38) line of the 9.7-µm band are studied experimentally. It is confirmed that the variation of relative amplitudes of the satellites is caused mainly by the fact that the magnitudes of the self-induced transparency of the medium that are created by each light wave for itself are different for the main resonances of the multiplet and for their satellites. The discrepancy between the experimental and theoretical dependences of the relative amplitudes of the satellites upon variation of the gas pressure and power of light waves is analyzed. Based on the discovered discrepancy, it is suggested that molecular collisions with Bennett dip or peak transfer contribute to the formation of satellites of the FEF multiplet. Multiphoton processes participate in the formation of one of the multiplets of the FEF multiplet. It is suggested that the power of the light field partially lifts the ban on transitions participating in the formation of satellites of both studied multiplets. Processing of the experimental curves by the leastsquares method revealed spectrally unresolved satellites within the FEF multiplet, which represent crossover resonances between allowed and forbidden transitions. For these satellites, no additional dependence of the amplitude on the laser power or gas pressure was found. The dependence of the amplitude of these satellites is completely determined by different for the main resonances and satellites magnitudes of self-induced transparency of the medium experienced by each light wave.

Compact stabilized semiconductor laser for frequency metrology.

We report on the development of a frequency modulatable 795 nm semiconductor laser based on self-injection locking to a high-quality-factor whispering-gallery-mode microresonator. The laser is characterized by residual amplitude modulation below -80 dB and frequency noise better than 300 Hz/Hz(1/2) at offset frequencies ranging from 100 Hz to 10 MHz. The frequency modulation speed and span of the laser exceed 1 MHz and 4 GHz, respectively. Locking of the laser to the Doppler-free saturated absorption resonance of the (87)Rb D1 line is demonstrated and relative frequency stability better than 10(-12) is measured for integration time spanning from 1 s to 1 day. The architecture demonstrated in this study is suitable for the realization of frequency modulatable lasers at any wavelength.

Polarization phenomena in the transparency and adsorption effects induced by the field of counterpropagating waves

The physical processes that form the resonances of saturated absorption and magnetic scanning in the field of counterpropagating waves of an arbitrary intensity when their polarizations change are numerically simulated. The atomic transition with level moment J = 1 is used as an example to show that the anomalies in the experimental saturated absorption spectra are determined by the degree of opening of the atomic transition. In the case of magnetic scanning, the anomalies are caused by the magnetic coherence induced by the wave fields at the levels of the lower state rather than by its transfer from the excited states, as was proposed earlier.

Narrowing of sub-Doppler saturated-absorption resonances in multilayer gas cells

We have studied theoretically nontrivial specific features of sub-Doppler resonances of saturated absorption in a multilayer gas cell with a rarefied gas medium, which is a compact analog of a large number of plane-parallel atomic beams. Spatially separated saturating and probing monochromatic laser beams that co- and counterpropagate (at the same frequency) in this cell have been considered. In this situation, the action of the light radiation of the saturating beam on the probing beam is determined by optically pumped atoms that fly between the beams under conditions that the longitudinal components of their velocities experience selection due to a specific geometry of the multilayer cell. Such a selection leads to a narrowing of the sub-Doppler resonance in the absorption of the probing beam and decreases the difference between the structures of this resonance for the cases of co- and counterpropagation of the saturating radiation. We have found that, in the considered multilayer cell, the effective width of the sub-Doppler resonance can be smaller (by a factor of about 1.5) than the extremely narrow characteristic width of the well-known Lamb dip in spectroscopy of saturated absorption in the standard gas cell. Results of this study can be used in atomic spectroscopy of ultrahigh resolution and for the laser-frequency stabilization.

Demonstration of a stable erbium-fiber-laser-based frequency comb based on a single rubidium atomic resonator

We propose a compact stabilization system for erbium(Er)-fiber-laser-based frequency comb with wavelengths ranging from 1510 nm to 1610 nm, which is widely used in fiber-based optical communication. In this stabilization scheme, both the repetition rate and mode of the comb is directly stabilized to a Rb atomic resonator, based on the physical phenomenon of coherent population trapping (CPT) and saturated absorption resonance, respectively. The stabilized frequency comb provides the long-term instabilities of ∼3 × 10−12 for repetition rate and of ∼7 × 10−12 for each optical mode of comb and can meet the requirement of optical-comb-based communication.

Coherent Resonance of Saturated Absorption in Spectroscopy of Counterpropagating Waves

Results of theoretical researches of the saturated absorption resonance shape in a method of the probing field on V-type of transitions are represented. It is shown that in case of opposite circulary polarized optical fields the resonance is shown in the form of cross, and its form strongly depends on relaxation constants of levels and it can be represented as in the form of a dip, and absorption peak. Thus the peak form has exclusively coherent character. Atomic transitions are offered, on which observation of the given effect is possible.