We develop a nonlinear theory of propagation of a monochromatic light wave in a gas of two-level atoms under the condition of inhomogeneous Doppler lineshape broadening, while considering a self-consistent solution of the Maxwell–Bloch equations in the mean-field approximation using a single atom density matrix formalism. Our approach shows a significant deformation of the Doppler resonant lineshape (shift, asymmetry), which depends on the atomic density. These effects are a consequence of only the free motion of atoms in a gas and is not associated with interatomic interaction. In particular, the frequency shift of the field-linear contribution to the transmission signal is more than an order of magnitude greater than the shift due to the interatomic dipole–dipole interaction, and the first nonlinear correction has an even stronger deformation, which exceeds the effect of the interatomic interaction by three orders of magnitude. The found effects caused by the free motion of atoms require a significant revision of the existing picture of spectroscopic effects, which depend on the atomic density in a gas.

The radiation of a two-level resonant medium that is placed into a cavity and is excited by a periodically phase modulated laser pulse is studied theoretically. The radiation is analyzed based on the analytical and numerical solutions of the system of Maxwell–Bloch equations under conditions of a strong coupling between the field and the matter. Under these conditions, this system is similar to a polariton laser. The excitation efficiency of a polariton laser by a phase-modulated radiation pulse is shown to be high compared to a pulse without phase modulation of the carrier frequency. It is shown that the main reason for the efficient excitation of polariton modes in the medium is the appearance of difference combination parametric resonance. The obtained results open up new possibilities for the excitation of radiation of polariton lasers by low-power frequency-modulated pump laser radiation.

In this paper, the radiation of a two-level resonant medium placed in a cavity and excited by a laser pulse with periodic phase modulation is studied theoretically. The analysis is carried out on the basis of an analytical and numerical solution of the system of Maxwell-Bloch equations under conditions when the regime of strong coupling of the field and matter is realized. Under these conditions, this system is similar to a polariton laser. A high excitation efficiency of a polariton laser by a phase-modulated radiation pulse compared with a pulse without phase modulation of the carrier frequency is shown. It is shown that the main reason for the effective excitation of polariton modes of the medium is the occurrence of a difference combination parametric resonance. The results obtained open up new possibilities in the excitation of radiation from polariton lasers by low-power pumping laser radiation with frequency modulation.

Впервые показано, что при изменении временных параметров возбуждающего импульса лазера (величина чирпа, длительность импульса и его амплитуда) можно управлять величиной и знаком эффекта " конденсации спектра" импульса на частоте резонансного перехода плотной резонансной среды.Важно отметить, что

The spectroscopic properties of Tm, Ho:KYW crystals with different Ho concentrations were investigated. The diode-pumped microchip laser operation of Tm (5 at.%), Ho (0.5 at.%): KYW and Tm (5 at.%), Ho (1 at.%): KYW was demonstrated. The highest, to our knowledge, output power of 480 mW with slope efficiency of 31% for CW Tm (5 at.%), Ho (0.5 at.%): KYW microchip laser was obtained.

For the first time, it is demonstrated that the magnitude and sign of the effect of spectral condensation of a laser pulse at the resonant-transition frequency of a dense medium can be controlled by changing the driving-pulse parameters (chirp, pulse width, and pulse amplitude). In the process of this, importantly, the driving-pulse energy and spectrum remain unchanged. Direct time-resolved measurements revealed an oscillatory character of the induced superradiance of rubidium vapors representing a long train of decaying short pulses. The width and repetition rate of the pulses in the train are determined by atomic density N-0 of the medium, while the width of an entire superradiance pulse (10 ps) is considerably larger than that of the driving laser pulse (50 fs).

We report on growth and detailed spectroscopic study of Eu3+-doped tetragonal sodium gadolinium double tungstate, Eu:NaGd(WO4)(2), a new promising crystal for deep-red lasers. Large-volume crystal doped with 4.9 at.% Eu is grown by Czochralski method along the [001] crystallographic direction. Absorption of Eu3+ ions is studied at room temperature (RT) and at 6 K. For the absorption band related to the F-7(1) -> D-5(1) transition suitable for pumping of Eu:NaGd(WO4)(2), the maximum cross-section is sigma(abs) = 1.2 x 10(-21) cm(2) at 535.5 nm with the full width at half maximum (FWHM) of 3.1 nm (at RT, for E parallel to a polarization). For the D-5(0) -> F-7(4) transition, the maximum stimulated-emission cross-section is sigma(SE) = 1.6 x 10(-21) cm(2) at 698.3 nm (RT, E parallel to c polarization). Lifetime of the D-5(0) state is 490 +/- 10 mu s (at RT). Under UV excitation, Eu:NaGd(WO4)(2) provides intense red emission with CIE coordinates (x = 0.671, y = 0329). (C) 2016 Elsevier B.V. All rights reserved.

We experimentally studied the superradiance of the resonant line of rubidium under femtosecond optical pumping of a dense extended medium without population inversion under conditions of strong lightmatter coupling. Substantial self-splitting of superradiance components is observed.

An optoacoustical gravitational detector that structurally combines the principles of interferometric and solid-state gravitational antennas is described. A large acoustical resonator, which is matched to a commensurate Fabry-Perot (FP) optical interferometer, serves as the sensitive element for recording changes in the gravitational-field gradient. In a test experiment, the spectral density of recorded spatial deformations (metric variations) was 10−19 Hz−1/2 at a frequency of ∼1.3 kHz within a band of ∼4 Hz, which can be extended by an order of magnitude upon a corresponding increase in the sharpness of the interferometer mirrors. The new antenna is designed for detecting relativistic catastrophes (collapses) in the Galaxy and the nearest vicinity during complex (multichannel) monitoring with neutrino telescopes of the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Sciences.

Исследованы свойства связанных долгоживущих состояний системы “электромагнитное поле + вещество”, возникающих при столкновении когерентных импульсов в плотной резонансной среде. Показано, что рассмотренная система обладает свойствами беззеркального высокодобротного поляритонного нанорезонатора.

The properties of coupled long-lived states of the electromagnetic field + matter system that are induced by a collision of two counter-propagating coherent pulses in a dense resonant media are discussed. It is demonstrated that the system possesses properties of a mirrorless polariton nanocavity with a high Q-factor.

We report on a comprehensive spectroscopic study of monoclinic Eu:KLu(WO4)2 crystal concerning its potential applications in red lasers. Optical absorption and stimulated-emission cross-section spectra are determined for this crystal for the principal light polarizations, E || Np, Nm and Ng. The maximum σSE corresponding to the 5D0→7F4 transition is 1.78×10−20 cm2 at 703.5 nm (for E || Nm). Spectroscopic properties of Eu:KLu(WO4)2 are modeled within the conventional Judd–Ofelt theory, as well as its modification for systems with an anomalously strong configuration interaction (ASCI), yielding absorption oscillator strengths, luminescence branching ratios for 5DJ→7FJ' transitions and radiative lifetimes of the 5DJ states. Photoluminescent properties of Eu:KLu(WO4)2 are studied under UV/visible excitation. Polarized Raman spectra are measured for Eu:KLu(WO4)2.

Monoclinic 2at% Eu-doped KY(WO4)2 is grown by top-seeded solution growth method. Polarization-resolved absorption and stimulated-emission cross-section spectra are determined for this crystal. Spectroscopic properties of Eu:KY(WO4)2 are modeled within conventional Judd–Ofelt theory, as well as theory of f–f transition intensities for systems with anomalously strong configuration interaction, yielding absorption oscillator strengths, luminescence branching ratios and radiative lifetime of 5D0 state. The impact of excited-state absorption from this state on possibility of laser operation is discussed. Photoluminescent properties of Eu:KY(WO4)2 are determined. This crystal provides intense red emission with CIE coordinates x=0.670, y=0.329.

Crystal growth, optical absorption and stimulated-emission are studied for Eu-doped monoclinic double tungstates, KRE(WO4)2 (with RE = Gd or Y). Free-running and Q-switched pulsed visible (702.8 nm, 5D0→7F4 transition) lasers, as well as quasi-CW and real-CW ones are realized with this crystal family, for the first time, to our knowledge.

Monoclinic Eu:KY(WO4)2 laser crystals are grown by TSSG method; polarization-resolved absorption and stimulated-emission cross-section spectra are determined for this crystal. Spectroscopic properties are modeled within ASCI theory. Under UV excitation, Eu:KY(WO4)2 provides intense red emission with CIE coordinates x = 0.670, y = 0.329.

[(Re x Lu y Y1–x–y )2O3]1–z (AO2) z laser ceramics have been synthesized, where Re is the rare earth element Nd3+ or Yb3+, A is the heterovalent ion Zr4+ or Hf4+, x = 1–5 mole%, y = 0–24 mole%, z = 0–12 mole%, by two methods: 1) from a mixture of nanopowders of the individual oxides and 2) from nanopowders of the given chemical composition. It is shown that the best characteristics are possessed by ceramics obtained using the second method. In the ceramics doped with zirconium and hafnium there takes place a broadening of the emission bands on the laser transitions of the neodymium ions of up to 36 nm, and of the ytterbium ions, of up to 75 nm. The effective lifetimes of the 4F3/2 level of the neodymium ion and of the 2F5/2 level of the ytterbium ion have been measured. It is shown that the effective lifetime of the 4F3/2 level of the neodymium ion is decreased by 5–6% when the yttrium oxide is doped with 12 mole% ZrO2 and is increased by roughly 30% when it is doped with 10 mole% HfO2. Quenching of luminescence of the neodymium ion is due to a Förster mechanism of decay of the 4F3/2 level of Nd3+. In this case, one of the channels of nonradiative population of this level is supported by the dipole-dipole interaction with the ions Zr3+ and Hf3+. The effective lifetime of the 2F5/2 level of the ytterbium ion in ceramics of such composition does not vary within the limits of measurement error.

Europium-doped monoclinic potassium gadolinium tungstate KGd. (WO4)2 crystals are grown by the top-seeded solution growth (TSSG) technique. Their absorption spectra are studied in detail for principal light polarizations, E broken vertical bar broken vertical bar N-p, N-m and N-g. It is accompanied by determination of absorption oscillator strengths by means of the theory of f-f transition intensities for systems with anomalously strong configuration interaction. Spectral and temporal characteristics of luminescence associated with D-5(0) -> F-7(J) transitions are analyzed, and luminescence branching ratios and the radiative lifetime of the D-5(0) state are determined. Stimulated-emission cross-section spectra are evaluated for Eu:KGd(WO4)(2) crystal. Pulsed Eu: KGd. (WO4)(2) lasers operating at room temperature at the wavelength of 702.8 nm (D-5(0) -> F-7(j) transition) are studied at Eu concentration of 10 = 25 at.%. Under laser pumping at 533.6 nm, a maximum output energy of 570 mu J is obtained. The main limitation for laser operation at D-5(0) -> 7F2 transition is strong excited-state absorption via the D-5(0) -> F-5(4) channel.