卷 40, 编号 1 (2019)

On the spin-1/2 example, we demonstrate that quantum states can be described by standard probability distributions, which contain the same information that the wave function and the density matrix do. Within the framework of this approach, called for spin-1/2 the quantum suprematism representation, the probability distributions are illustrated by simplex or triangle geometry or by the Triada of Malevich’s Squares (black, red, and white) associated with the triangles, and new quantum relations for areas of the squares are obtained. The superposition principle for spin states and quantum interference phenomenon are expressed as an explicit new nonlinear addition rule for the probability distributions describing the quantum states and illustrated as the addition of two Triadas of Malevich’s squares. We discuss some analogy of the triangle geometry of spin-1/2 states related to the O(3) symmetry group and the pyramide geometry related to the hydrogen-atom dynamical symmetry O(2, 4).

We estimate the quantum state of a two-level atom and the coherent field in a Kerr medium subject to the cavity damping. The density matrix of the field is considered within the framework of the dispersive approximation. We study dynamical properties of the linear entropy, Wehrl entropy, and the Wehrl phase density during the time of interaction. The effects of the Kerr medium and cavity damping on the time evolution of different quantities are examined. The results refer to the sensitivity of these aspects to changes either in the decay parameter or in the Kerr-like medium and Stark-shift parameters. Linear entropy and nonclassical properties of the field quantified by the Wehrl entropy are also very sensitive to the Kerr medium and Stark-shift parameter.

We calculate the amplitudes of surface plasmon-polaritons (SPP) excited at a photonic-crystal–metal interface. Using a three-wave approximation, we evaluate optical fields in the crystal medium. The generation of plasmons at the boundary between the photonic crystal (PhC) and gold substrate is numerically analyzed in the wavelength range of a plane incident wave 400–1,900 nm. The optimum wavelength corresponding to the maximum plasmon amplitude is determined.

We study the formation of a spark channel in an atmospheric discharge on a nanosecond time scale using picosecond laser interferometry. We elaborate the approach to obtain reliable data on the electron density of the developing spark channel. We describe in detail the procedure for tracing and processing the interferograms and obtaining 2D-phase maps as well as the features of the electron density reconstruction. We found that the electron density of the spark channel can be as high as n_e≈ 5 · 10¹⁹ cm⁻³. This value exceeds the number density n_m≈ 2.7 · 10¹⁹ cm⁻³ of atmospheric air. We demonstrate that the plasma with such extreme electron density is concentrated near the cathode and in the central core (≈ 20 μm in size) of the developing spark channel. Also we show that the electron density is nonuniformly distributed along the spark channel. From the cathode surface to the top of the spark channel, the electron density drops down to n_e≈ 2 · 10¹⁹ cm⁻³. In contrast to that, the linear electron density is approximately constant along the spark channel and reaches a value of N_e∼ 10¹⁴ cm⁻¹.

We investigate the temporal correlations of radiation intensities of a multimode Fabry–Pérot semiconductor laser. Strong intensity correlations with a fixed phase shift between different longitudinal modes of the laser are revealed. The second g⁽²⁾ and third g⁽³⁾ order intensity correlation functions are studied to clear the character of the intermodal coupling.

We demonstrate a diode-pumped acousto-optically (A-O) Q-switched 1,066 nm laser with a novel Nd:Gd_0.69Y_0.3TaO₄ mixed crystal. At a modulation repetition rate of 10 kHz and an absorbed pump power of 15 W, the pulsed laser output characteristics are: average output power 2.41 W, pulse width 27.2 ns, pulse energy 241 μJ, and pulse peak power 8.86 kW. At a modulation repetition rate of 20 kHz and an absorbed pump power of 15 W, the characteristics are: average output power 2.68 W, pulse width 30.1 ns, pulse energy 134 μJ, and pulse peak power 4.45 kW.

We report a passively Q-switched all-fiber Yb-doped laser using the structure of step-index multimode fiber and graded-index fiber (SIMF-GIMF) as a new saturable absorber (SA) based on the nonlinear multimode interference (NL-MMI). Through bending the SA to a certain state, we obtain a stable Q-switched laser operation with the shortest pulse duration of 4.37 μs and a corresponding repetition rate of 147.6 kHz with center at 1,039 nm. The maximum average output power and single pulse energy are recorded to be 2.409 mW and 16.3 nJ, respectively. To the best of our knowledge, this paper confirms experimentally for the first time Q-switched laser operation based on SIMF-GIMF SA in all-fiber lasers. In addition, we also observed unstable Q-switched mode-locking operation. All-fiber lasers based on SIMF-GIMF SA are attractive for practical applications and undergo no damage and performance degradation with time.

We report a high-peak-power, short-pulse-width LD end-pumped doubly Q-switched Nd:YAG 946 nm laser. Using an acousto-optically Q-switch and a Cr⁴⁺:YAG saturable absorber, doubly Q-switched operation in 946 nm laser is conducted at 3 kHz. Maximum peak power of 17.8 kW is achieved with a pulse width of 15.5 ns in doubly Q-switched 946 nm laser operation.