In this work, we created a source of ultracold atoms for a quantum interferometer-gravimeter. A cloud of $10^{7}-10^{8}$ atoms with the temperature of around 6 uK was obtained. An effective selection of rubidium atoms in the nonmagnetic sub-state was carried out.

The results of theoretical and experimental studies aimed at the creation of matter wave interferometers with Mg atoms are presented. Atom-optical interferometers based on the Ramsey-Bordé scheme are of great interest for the development of optical frequency standards. Ultracold Mg atoms are promising for the development of an optical frequency standard with relative uncertainty and long-term frequency instability at a level of 10−17 − 10−18. A long-term frequency stability of 3·10−15 is obtained at an averaging time τ = 103 s while stabilizing the frequency of a ‘clock’ laser at 457 nm (1 S 0 → 3 P 1 transition) to narrow Ramsey-Bordé resonances of Mg atoms cooled and localized in a magneto-optical trap. The measured frequency stability is determined by the stability of the measurement system based on an optical frequency comb stabilized to the optical frequency of a Yb:YAG/I2 standard. We also present the results of theoretical studies aimed at the use of Mg atom interferometers based on Bragg diffraction for quantum sensing.

We report on the development of a highly stable source of 457-nm radiation based on a diode laser and a tapered amplifier operating in a double-pass scheme. The diode laser frequency was stabilised by a high- Q reference Fabry – Perot interferometer and doubled in a PPSLT nonlinear crystal placed in an enhancement cavity. At a maximum output power of 200 mW at a wavelength of 457 nm, the laser linewidth was less than 5 kHz. The radiation source operation was demonstrated in experiments on precision spectroscopy of cold magnesium atoms in a magneto-optical trap.

Experimental studies aimed at developing an optical frequency standard based on ultracold magnesium atoms with a relative uncertainty of Delta nu/nu < 10(-16) are performed. The frequency of the clock laser system at a wavelength of 457 nm is stabilised to narrow optical resonances ( Ramsey fringes) in time-separated laser fields interacting with cold magnesium atoms localised in a magneto-optical trap ( MOT). The frequency stability of the laser system is investigated using a femtosecond comb based on a Ti : sapphire laser. Long-term frequency stability ( determined by the Allan function) of similar to 5 x 10(-15) at averaging time tau = 1000 s is obtained.

This paper presents the recent experimental results on development of an optical frequency standard based on ultra cold magnesium atoms with relative frequency uncertainty and long term stability at the level of Δv/v <10−16. We stabilized the frequency of our clock laser system at 655 THz to narrow Ramsey fringes in a time separated laser fields interacting with cooled Mg atoms localized in a magneto-optical trap (MOT). The intercombination line 1S0→3P1 was used as the reference for frequency stabilization. The results of stabilization were studied with femtosecond comb based on Ti:Sa laser.

Two approaches for solving the long-standing problem of deep laser cooling of neutral magnesium atoms are proposed. The first one uses optical molasses with orthogonal linear polarizations of light waves. The second approach involves a 'nonstandard' magneto-optical trap (NMOT) composed of light waves with elliptical polarizations (in general). Both the widely used semiclassical approach based on the Fokker-Planck equation and quantum treatment fully taking into account the recoil effect are employed for theoretical analysis. The results show the possibility of obtaining temperatures lower than 100 mu K simultaneously with a large number of cold atoms similar to 10(6) divided by 10(7). A new velocity-selective cooling technique allowing one to reach the microkelvin temperature range is also proposed. This technique may have some advantages over, for instance, the shallow-dipole-trap technique utilized by other authors. In the case of magnesium atoms this new technique may be used for obtaining a large number of ultracold atoms (T similar to 1 mu K, N > 10(5)). Such a large number of ultracold atoms is crucial issue for metrological and many other applications of cold atoms.

Deep laser cooling of Mg-24 atoms has been theoretically studied. We propose a two-stage sub-Doppler cooling strategy using electrodipole transition 3(3)P(2) -> 3(3)D(3) (lambda = 383.8 nm). The first stage implies exploiting magneto-optical trap with sigma(+) and sigma(-) light beams, while at the second stage lin perpendicular to lin molasses is used. We focus on achieving a large number of ultracold atoms (T-eff < 10 mu K) in a cold-atomic cloud. The calculations have been based on quantum treatment, taking into full account the recoil effect and beyond many widely used approximations. Steady-state values of average kinetic energy and linear momentum distributions of cold atoms have been analyzed for various light-field intensities and frequency detunings. The results of conducted quantum analysis have been significantly different from the results achieved under a semiclassical approximation based on the Fokker-Planck equation. The second cooling stage allows achieving sufficiently lower kinetic energies of the atomic cloud as well as increased fraction of ultracold atoms at certain conditions compared to the first one. We hope that the obtained results can help in overcoming current experimental problems in deep cooling of Mg-24 atoms by means of laser field. Cold magnesium atoms cooled in a large amount to several mu K are of huge interest to, for example, quantum metrology and to other many-body cold-atoms physics.

The two-stage laser cooling strategy for 24 Mg is proposed. The calculations based on quantum treatment with full account for the recoil effect. The results can assist overcoming current difficulties in deep laser cooling of magnesium.

We present the theoretical analysis of sub-Doppler laser cooling of Mg-24 atoms using dipole transition 3(3)P(2)-> 3(3)D(3) under two counterpropagating light waves with opposite circular polarizations (one-dimensional sigma(+)sigma(-) configuration). For numerical calculations the standard semi-classical approach based on the Fokker-Planck equation for linear momentum distribution of atoms is exploited. The distributions are gained beyond the limits of slow atoms approximation and for an arbitrary light field intensity. The absence of these limits allows us to determine the optimal parameters of the light field to maximize a fraction of ultracold atoms (T similar to 10 mu K) in a whole atomic cloud. In particular, under certain conditions the fraction can reach a value of 50%. Solution of the existing problems in deep laser cooling of magnesium atoms has obvious prospects for atomic optics and quantum metrology: for instance, in designing new-generation optical frequency and time standards based on cold atoms in optical lattices.

We present the theoretical analysis of sub-Doppler laser cooling of 24Mg atoms using dipole transition 33P2→33D3 under two counterpropagating light waves with opposite circular polarizations (one-dimensional σ+σ– configuration). For numerical calculations the standard semi-classical approach based on the Fokker–Planck equation for linear momentum distribution of atoms is exploited. The distributions are gained beyond the limits of slow atoms approximation and for an arbitrary light field intensity. The absence of these limits allows us to determine the optimal parameters of the light field to maximize a fraction of ultracold atoms (T ~ 10 μK) in a whole atomic cloud. In particular, under certain conditions the fraction can reach a value of 50%. Solution of the existing problems in deep laser cooling of magnesium atoms has obvious prospects for atomic optics and quantum metrology: for instance, in designing new-generation optical frequency and time standards based on cold atoms in optical lattices.

We report the results of experimental investigations aimed at creation of the optical frequency standard based on magnesium atoms cooled and localised in a magneto-optical trap (MOT). An experimentally realised MOT for magnesium made it possible to obtain a cloud comprising atoms at a temperature of . The results of ultra-high resolution spectroscopy of intercombination transition for Mg atom are presented, the resonances in time-domain separated optical fields with the half-width of are recorded, which corresponds to the -factor of the reference line .

Работа выполнена при поддержке Минобрнауки РФ в рамках ФЦП «Научные и научно-педагогические кадры инновационной России» на2009–2013 гг. (ГК16.740.11.0466), РФФИ (гранты №12-02-00454, 12-02-00403, 11-02-00775, 11-02-01240, 10-02-00406), РАН и Президиума Сибирского отделения РАН. Исследования М. Ю. Басалаева, Д. В. Бражникова, Р. Я. Ильенкова, А. М. Шилова были поддержаны также грантом Президента РФ(МК-3372.2012.2) и грантом РФФИ(№12-02-31208-«мол_а»).

A new type of compact magnesium cell with room-temperature walls have been developed for high resolution spectroscopy on the Mg S-1(0)-P-3(1) intercombination line. Saturation resonances with a FWHM of 1.3.MHz have been detected in this cell in the fluorescence signal. The time selection method was applied to eliminate the background signal caused by the scattering of laser beams on cell windows. The signal-to-background ratio drastically increased by the spatial localization of excited atoms owing to collisions with atoms of a low-pressure inert gas.

Absorption at the S-1(0) - (3)p(1) intercombination transition in magnesium atoms is studied experimentally. The saturated absorption resonance of thermal magnesium atoms in a compact low-pressure absorption cell with walls at room temperature was recorded for the first time by using the spatial trapping of excited magnesium atoms in the detection region and the time separation of luminescence excitation and detection.

A ~20-mW cw radiation source is developed emit-ting at a wavelength of 457 nm with the linewidth less than 30 kHz. The source is based on a Ti:sapphire laser with freq-uency doubling in an external cavity containing a nonlinear LBO crystal. The results of high-resolution spectroscopy of magnesium atoms in separated optical fields, which demonstrate the possibilities of the system, are presented.

The results of saturated absorption spectroscopy of the intercombination 1 S 0 – 3 P 1 transition of magnesium atoms at 457 nm in an external absorption cell are presented. A laser system based on a Ti:Sa laser with frequency doubling in a LBO nonlinear crystal was used in these experiments. Saturated absorption resonances of magnesium in an external cell at the 1 S 0 – 3 P 1 transition have been obtained for the first time. Pressure broadening of resonances equal to 12.5±1.5 kHz/mTorr has been measured.

The results of saturated absorption spectroscopy of the intercombination S-1(0)-P-3(1), transition of magnesium atoms at 457 nm in an external absorption cell are presented. A laser system based on a Ti:Sa laser with frequency doubling in a LBO nonlinear crystal was used in these experiments. Saturated absorption resonances of magnesium in an external cell at the S-1(0)-P-3(1), transition have been obtained for the first time. Pressure broadening of resonances equal to 12.5 +/- 1.5 kHz/mTorr has been measured. (C) 2001 Elsevier Science B.V. All rights reserved.