The temporal dynamics of three-photon 5S1/2 → 5P3/2 → 6S1/2 → 39P3/2 laser excitation of mesoscopic ensembles of cold Rb atoms to Rydberg states in a magneto-optical trap is studied using cw single-frequency lasers at each stage. The ensembles comprise N = 1 – 5 atoms and are detected by the method of selective field ionisation with postselection with respect to the number of atoms. The dependence of the excitation probability on the duration of the exciting laser pulses and the number of detected Rydberg atoms is investigated. At short interaction times, a linear increase in probabilities is observed, and at large times, the probabilities reach saturation, while each number of atoms has its own characteristic features. The experimental dependences are compared with the results of numerical calculations in the framework of a four-level model, and their good agreement is obtained. The conditions necessary for observing Rabi population oscillations are determined. The obtained results are important for the application of Rydberg atoms in quantum information.
The possibility of obtaining superfluid phases for a Fermi gas of dysprosium with a magnetic dipole – dipole interaction is discussed. The obstacles and possible solutions are shown. The required phases are similar to the A1 phase and the polar β phase in 3 He. It is expected that in dysprosium, the macroscopic properties of the phase will be determined by the symmetry of the pair interactions. It is assumed to observe the kinetics of phase formation and spontaneous choice between two energy-degenerate phases with different projections of the orbital angular momentum.
A numerical model is constructed for calculating lightning-induced rapid changes in the polarisation state of a light signal at the output of a fibre-optic communication line with an optical ground wire. It is shown that taking into account anisotropy of real optical fibres has a noticeable effect on the shape of the polarisation rotation speed time profile. It is found that the maximum rate of change in the polarisation state and its temporal profile depend on the location of the lightning strike in the fibre span, the magnitude of fibre anisotropy and the direction of propagation of a light wave.
Laser oscillation is obtained in caesium and rubidium atoms with wavelengths in the range of 2 – 5.5 μm under pumping to high-lying energy levels. Longitudinal resonant pumping is implemented using the second harmonic of radiation from an optical parametric oscillator. The pump wavelength is tuned over discrete levels from 8P to 10P in caesium atoms and from 6P to 8P in rubidium atoms. The width of the pump radiation spectrum is 12 cm−1. When caesium atoms are pumped, the pump pulse energy is no more than 10 mJ; when rubidium atoms are pumped, it does not exceed 3 mJ. The pulse repetition rate is 10 Hz. The maximum output energy of IR laser radiation upon pumping the 9P3/2 level of caesium atoms is about 100 μJ at a cell temperature of ∼170°C, while the efficiency of pump conversion into radiation energy with a wavelength λ ∼ 3.1 μm turns out to be ∼1 %. For rubidium atoms, an estimate of the output energy of IR radiation gives a value of ∼80 μJ at a cell temperature of 180 °C, which corresponds to an energy efficiency of ∼2.7 %.
We report the results of studies of the lasing characteristics of an organic solid-state tunable laser with a polymethylmethacrylate matrix doped with Chromene 3, Pyrromethene 567, and Pyrromethene 597 dyes. The features of lasing when using selective and nonselective cavities are described. Tuning of the laser wavelength with a spectral linewidth of 0.018 nm in the range 550 – 628 nm is obtained on three polymer laser-active media emitting in the yellow and red spectral regions.
It is shown that the image contrast in the air when using a microscope based on dielectric microparticles with a size of the order of wavelength can be significantly enhanced with the help microparticles that provide the formation of the radiation localisation region at an angle to the direction of radiation incidence (at an angle to the optical axis). For this purpose, a screen is placed in front of the particle, which blocks part of the incident beam, forming a photonic hook or a photonic jet (terajet) with oblique illumination in the near field.
A model of the interference of fields from backscattering point sources in a ring optical resonator is presented. Examples of calculations of complex coupling coefficients in ring resonators of laser gyroscopes are given. Comparison of the calculation results with the results of model experiments demonstrates good agreement and makes it possible to determine dissipative and conservative backscattering components of individual resonator mirrors. The possibilities of reducing the dissipative and conservative backscattering components in the process of ring resonator alignment are discussed.
Single-cascade 1.56-to-2.84 μm SRS conversion is demonstrated in a hollow-core revolver fibre filled with methane at a pressure of 25 atm under pumping by positively chirped pulses of a high-power erbium-doped all-fibre laser. At a maximum pump pulse energy of 34 μJ (average power 3.74 W) and a pump pulse duration of about 260 ps, ultrashort pulses (USPs) with a duration of 110 ps and an energy of 1.33 μJ (average power 133 mW) are achieved at the centre wavelength of 2.84 μm. The gas fibre Raman lasers based on hollow-core fibres with pumping by high-power fibre sources are promising for producing all-fibre systems emitting USPs in the mid-IR range.
The characteristics of high-power semiconductor lasers with an 800 mm emitting aperture based on tunnel-coupled InGaAs/ AlGaAs/GaAs heterostructures with three optically uncoupled laser sections are studied. The maximum power achieved under pumping by current pulses with an amplitude of 47 A and a duration of 1 ms is 110 W with the maximum active region heating not exceeding 4.7 degrees C. At a pulse duration of 860 ms, the maximum optical power is 22.6 W, and the decrease in the optical power to the pulse end reaches 6.7 %. A decrease in the laser pulse duration to 85 ms leads to an increase in the peak laser power to 41.4 W at a pump current amplitude of 20 A.
Using the method of molecular dynamics, the expansion of a two-component, pulsed laser-produced ultracold plasma is directly calculated for various values of the number and density of particles and their electron temperatures. A new method is presented for generating and diagnosing a steady-state ultracold plasma formed under continuous wave laser irradiation. The performed calculations show the difference in the properties of an ultracold plasma obtained by pulsed and continuous wave laser irradiation.
We have investigated a multipass Yb : KGW disk amplifier based on the White cell configuration and pumped by a laser diode with a fibre output. It is shown that the three-mirror layout of the cell is three times more efficient than the four-mirror one, since the size and position of the signal beam on the surface of the active element do not depend on the cell number of passes. For a three-mirror cell scheme, a small-signal gain G = 168 is obtained in experiments for a pump power of 360 W. The experimentally achieved gain of two such amplifiers arranged in series is 6 × 104, which exceeds G 2 approximately two-fold.
A new method for two-stage laser enrichment of carbon-13 (13C) by isotope-selective IR multiphoton dissociation of Freon molecules is considered, which makes it possible to achieve a concentration of 13C up to 99 % or higher with high productivity. At the first stage, as a result of the selective dissociation of CF2HCl (Freon-22) molecules, it is expected to obtain a C2F4 dissociation product enriched in 13C up to 30 % – 50 %. At the second stage, CF2Br2 (Freon-12B2) is proposed to be used as a working substance, which is synthesised from enriched C2F4, and the enrichment process is carried out by selective deep ‘burning-out’ of the 12C-containing component. Experiments on multiphoton dissociation of Freon-12B2 with an initial 13CF2Br2 concentration of 30 % in a mixture with oxygen by pulsed CO2 laser radiation are performed. It is shown that reaching a 13CF2Br2 concentration of no lower than 99 % is possible at high values of the elementary separation act parameters: 15 % – 18 % dissociation yield and 40 – 75 selectivity for 12CF2Br2 molecules.
The splitting of the first and second transitions in the lutetium photoionisation scheme is studied in a wide range of laser radiation intensities, and the Rabi frequencies as functions of the radiation intensity are determined. Based on the results, we have obtained the decay branching coefficients of 0.54 and 0.41 for the first and second transitions, respectively.
Optical frequency combs have revolutionised accurate frequency and time measurements and have enabled broadband and simultaneously high resolution spectroscopic measurements that were not previously possible. This paper is an overview of the main results of the previously performed work, describing a new approach to extending frequency combs to the mid-infrared 'molecular signature' range using a subharmonic generator based on an optical parametric oscillator operating in degenerate mode. Such an instrument acts as an efficient frequency divider that rigorously down-converts and augments the spectrum of a pump laser frequency comb while maintaining its coherence. Our recent result is the demonstration of a subharmonic system with a two-octave spectrum, 3 - 12 mu m, which covers vibrational resonances for most molecular species. Potentially, through frequency division in the coherent sub-harmonic optical parametric amplifier regime, this method can be used to obtain intense long-wavelength pulses for high-field physics applications.
A two-channel double-pass iodine explosively pumped photodissociation laser (EPPL) with an explosively pumped master oscillator (MO) and an SBS mirror is studied. The radiation source, determined by an aperture 6 mm in diameter, through which the radiation from MO enters the turbulent surface air path, is located at a distance of 2.5 km from the amplifier unit input. An SBS mirror with a kinoform raster of microlenses is used to compensate for the amplifier and path optical inhomogeneities and to match the phases in the EPPL channels. The energy and spatial characteristics of the EPPL output radiation are studied experimentally and numerically. Good agreement is obtained between the experimental and calculated distribution of the energy density of the output EPPL radiation in the plane of the MO aperture, which is a pattern of interference between the two channels. The maximum energy density in the aperture plane is by more than 4 times greater than in the case of a single-channel EPPL.
At the end of December 2021, there was held online the annual, fifteenth in a row, All-Russian Conference on Physics of Ultracold Atoms, in which scientists from other countries took part. Over the past years, this conference has changed dramatically: from a one-day workshop of participants in the integration projects of the Siberian Branch of the Russian Academy of Sciences, where the results of the year were summed up, into a full-scale All-Russian conference with a wide geographic coverage of participants from Vladivostok to Voronezh. Foreign scientists also took an active part in the work of the conference, but until recently they were Russianspeaking researchers, and so Russian remained the working language of the conference. In 2021, an important step was taken towards its transition to a full-fledged international format. Russian and English became the working languages, and in order to increase the level and significance of the conference, as well as to deepen international cooperation in this field of physics, a number of foreign scientists were invited.
We investigate displacement measurements of up to 17 μm on a heterodyne laser interferometer laboratory model. The measurement error for small (up to 200 nm) linear displacements is found to be 270 pm at a 10-s averaging time. The results obtained can be used for developing a space laser interferometric system for the global Earth’s gravity field mapping.
We report the development of a group of luminescent fibre-optic temperature sensors that use Ce3+-, Dy3+-, and Yb3+- doped yttrium aluminium garnet (YAG) nanophosphors as thermosensitive materials. The nanophosphors have been prepared in the form of powders with a crystallite size from 19 to 27 nm by a polymer – salt method and exhibit bright luminescence at 550 (YAG : Ce3+), 400, 480 (YAG : Dy3+), and 1030 nm (YAG : Yb3+). The sensor design includes a silica capillary, partially filled with a nanophosphor, and two large-aperture multimode optical fibres located in the capillary, which deliver excitation light and receive and transmit the photoluminescence signal. The photoluminescence signal amplitude of all the sensors decreases exponentially with increasing temperature, pointing to characteristic thermal quenching of photoluminescence and adequate operation of the devices up to 500 °C. The highest temperature sensitivity among the fibre-optic sensors is offered by the YAG : Ce3+ nanophosphor-based devices.
A pump – probe configuration is used to register zero-field level-crossing resonances in Rb vapour contained in a cell with antirelaxation coated walls. The scheme is applied to detect the weak magnetic field generated by a current-carrying micro-wire (metallised track). Such micro-wires can be employed in neural prostheses and hybrid bionic systems as micro-electrode arrays. More specifically, the operation of such live micro-wire belonging to a neuronal – electrode interface is demonstrated, which indicates the possibility of remote testing of the operation (conducting/nonconducting) of micro-wires for in neural implants.
