No abstract available

[en] Laboratory methods for detecting possible time variation in the fine structure constant are reviewed. Such methods provide a large amount of controllability while at the same time approaching astrophysical tests in terms of sensitivity to the linear drift. Modern high-precision spectroscopic experiments involving atomic transition frequency measurements against the primary ¹³³Cs standard are reviewed. Combining results from different laboratory spectroscopic measurements allows contributions from the electromagnetic and strong interactions to be disentangled. (reviews of topical problems)

[en] Precision methods for measuring the hyperfine splitting E_HFS(2S) of the metastable level in light hydrogen-like systems such as hydrogen, deuterium, and the ³He⁺ ion are considered. These measurements open up a new possibility for precise testing of quantum electrodynamics (QED) of bound states in hadronic systems. While the direct calculation of the energy levels in such systems runs into the problem of the uncertainty of the nuclear charge radius, the contribution of energy corrections appearing in the calculation of the parameter D₂₁ = 8E_HFS(2S) - E_HFS(1S) taking the finite size of the nucleus into account becomes smaller. The results of calculations of D₂₁ are presented and compared with experimental values. The approach considered in the paper allows the testing of some bound-state QED corrections to the hyperfine splitting energy at a level of 10^-7, which is comparable with the results of precision QED tests based on the study of the hyperfine splitting in leptonic systems. (invited paper)

[en] An investigation was made of the potentialities of aperiodic multilayer structures (AMSs) optimised to obtain a preassigned reflection spectrum in the x-ray range (λ < 300 A) and also starting from other criteria. It was found that among the multitude of realisations of AMSs there exist those which are superior to the regular structure in width of the operating range, integral reflectivity, and peak reflectivity. New types of x-ray optical elements are proposed on a basis of AMSs. AMSs were derived which possess a constant normal-incidence reflectivity R at normal incidence throughout the 130 - 190 A (R=24 %), 130 - 300 A (R=15%), etc., ranges. We found AMSs which possess a high polarising power (polarisance) and a constant R in a broad wavelength range for a fixed angle of incidence. AMSs possessing several isolated reflection peaks which are not Bragg peaks of one another, were calculated. AMSs intended for operation in the hard x-ray range at grazing incidence of radiation were optimised. The technique elaborated in our work was demonstrated to be efficient for optimising AMSs with a very large (∼10³) number of layers. (laser applications and other topics in quantum electronics)

[en] A laser system with a narrow generation line for secondary laser cooling of ⁸⁷Sr atoms has been developed and investigated. It is planned to use ultracold ⁸⁷Sr atoms loaded in an optical lattice in an optical frequency standard. To this end, a 689-nm semiconductor laser has been stabilised using an external reference ultrastable cavity with vibrational and temperature compensation near the critical point. The lasing spectral width was 80 Hz (averaging time 40 ms), and the frequency drift was at a level of 0.3 Hz s^-1. Comparison of two independent laser systems yielded a minimum Allan deviation: 2 × 10^-14 for 300-s averaging. It is shown that this system satisfies all requirements necessary for secondary cooling of 87Sr atoms using the spectrally narrow ¹S₀ — ³P₁ transition (λ = 689 nm). (cooling of atoms)

[en] We describe a panoramic stigmatic spectrograph comprising a grazing-incidence toroidal mirror and a large-aperture free-standing transmission diffraction grating (5000 lines mm^-1 ). Two spectrograph versions were constructed, with grazing angles of 7.6 and 4⁰ and the short-wavelength spectral limits near 4 and 1.5 nm. The spectrograph aberrations were studied by numerical ray tracing. The spectrograph was used to record line and quasi-continuous spectra (1.5 - 30 nm) of multiply charged ions in a plasma generated by the second-harmonic pulses of an yttrium aluminate laser (Q = 0.15 J, τ = 5 ns, λ = 0.54 μm, repetition rate = 0.5 Hz). In combination with a laser-produced plasma radiation source, the arrangement was used to characterise soft x-ray optical components and to generate collimated beams of polarised radiation in the 14 - 20 nm range. (laser applications and other topics in quantum electronics)

No abstract available

[en] The number of laser cooled and trapped thulium atoms in a magneto-optical trap is increased by a factor of 3 using a two-dimensional optical molasses which collimated the atomic beam before entering a Zeeman slower. A diode laser operating at 410.6 nm was employed to form optical molasses: The laser was heated to 70 °C by a two-step temperature stabilisation system. The laser system consisting of a master oscillator and an injection-locked amplifier emitted more than 100 mW at 410 nm and had a spectral linewidth of 0.6 MHz. (extreme light fields and their applications)

[en] Resonances of coherent population trapping were detected in atomic vapours of the rare-earth element samarium. The coherent population trapping was produced by two external-cavity diode lasers (672 and 686 nm) in a Λ-system formed by the three levels of ¹⁵⁴Sm: the 4f⁶6s²(⁷F₀) ground state, the first fine-structure 4f⁶6s²(⁷F₁) sublevel of the ground state and the 4f⁶(⁷F)6s6p(³P^o)⁹F^o₁ upper level. The dependence of the spectral shapes and resonance contrasts on the polarisation of the laser beams and the direction of the applied magnetic field was studied. The obtained results were analysed. (nonlinear optical phenomena)

[en] The influence of noises of the frequency and phase difference of an exciting bichromatic field on the parameters of coherent population trapping resonances is studied experimentally. When the phase difference fluctuates within a limited interval near its average value with a short correlation time, the resonance contrast decreases proportionally to exp(φ²_rms), where φ²_rms is the phase dispersion (in rad²). In this case, the spectral width of the resonance remains constant. In another limiting case, when the phase noise has a long correlation time, the resonance contour broadens, the area under the contour being invariable. Experiments were performed with the Zeeman sublevels of the ground state of ⁸⁷Rb by exciting rubidium vapour in a glass cell at the resonance wavelength of 795 nm. (interaction of laser radiation with matter)