Energy Characteristics of Non-Resonator Generation in Nanodispersed Active Media Irradiated with Femtosecond Laser Pulses

Russian Physics Journal - Results of experimental measurements of the energy characteristics of stimulated emission in coumarin-30 and rhodamine 6G dyes with nanoparticles under irradiation with...     

Stimulated Emission Thresholds of Ethanol Solution of Coumarin-30 Dye with Incorporated ZnO Nanoparticles Upon Irradiation with Femtosecond Laser Pulses

Russian Physics Journal - Experimental results of measuring the threshold power density of stimulated emission in coumarin-30 dye solutions with ZnO nanoparticles upon irradiation with femtosecond...     

Effect of the domain structure on ferromagnetic resonance in easy-axis ferromagnets

The results of experimental and theoretical investigations of ferromagnetic resonance (FMR) in ferrite single crystals having hexagonal structure and magnetocrystalline anisotropy of the easy-axis type are reported. Experiments are carried out on disk-shaped samples of materials differing in anisotropy strength. The values of the effective anisotropy fields and the gyromagnetic ratios (g-factors) of the materials are determined from measured frequency dependences of the FMR field along the easy and hard magnetization directions for homogeneously magnetized samples. It is shown that if the FMR spectra are also measured for the same samples in the presence of a domain structure, then one can experimentally determine not only the above-mentioned parameters but also the saturation magnetization of uniaxial magnetic materials. It is shown that the theory of the FMR frequency spectrum of a partially magnetized sample with a simple domain structure in the form of a system of plane-parallel layers is in good agreement with the experiment.     

Interaction of femtosecond pulses of a two-harmonic Ti:Sapphire laser with liquid media

The interaction of ultrashort laser pulses having wavelengths of 400 and 800 nm with liquid media, including organic solutions, has been experimentally studied. It is shown that transparent drops evaporate and boil (with partial mass ejection in the form of vapor and liquid fragments) in the field of ultrashort light pulse. A large-scale change in the spectrum of laser pulse during its interaction with a water particle is revealed. This change is caused by self-modulation of the light phase due to the Kerr optical nonlinearity of liquid and the formation of plasma. Filamentation in continuous liquid media is analyzed; specifically, the dependences of the number of filaments, the lasing spectrum width, the nonlinear-focusing distance, and the filamentation region diameter on the laser pulse power are measured. It is noted that there is a range of relative powers where the number of filaments very rapidly increases. It is shown that the spectral broadening at filamentation, observed for fixed pulse energy with a change in pulse width, overlaps the entire visible spectral range. This circumstance makes it possible to obtain width-tunable pulses and use them, e.g., in optoacoustic diagnostics of media.     

Low-coherence doppler lidar with multiple time coherence of reference and probe waves

The notion of multiple time coherence of optical beams is introduced and mathematically analyzed for the first time. Mathematical simulation is used to demonstrate the possibility of the generation of multiple fiber pulses (MFPs), which exhibit multiple time coherence, and the possibility of their application for the laser Doppler anemometry of spatially separated scattering objects (including the realization of wind coherent Doppler lidars). A method to obtain MFPs of a given duration with the means of fiber-optic commutation is proposed. The method is based on nanosecond lasers with a limited coherence length realized in a set of fiber topologies. The concept of a low-coherence Doppler lidar with the multiple time coherence of the reference and probe waves is formulated. The energy parameters of the lidar are mathematically simulated for one of the topologies of the MFP device.     

Basic principles of pulsed-wind Doppler lidars with multitime coherence

A concept of multitime coherence (MTC) of optical beams is proposed. Two versions of fiber multiplicator topologies are presented, which are intended for the generation of multiple fiber pulses (MFP) possessing the MTC property. The fiber multiplicators may be a useful tool for Doppler laser anemometry of spatially separated scattering objects. Moreover, their use makes feasible the implementation of low-coherence wind Doppler lidars on the base of laser sources having a limited-time coherence (from one to a few tens of nanoseconds) and a high-velocity measurement resolution. Different lidar systems that feature a ring-fiber resonator (RFR) for reference wave generation are proposed. Two systems are also considered: (i) one based on a multimode fiber topology, which provides for the sensing ns-pulse generation and for the reference and probe wave multiplication; (ii) one based on a single-mode fiber topology, which provides for ns-pulse sensing and for the signal and reference wave multiplication. The concept of a low-coherence Doppler lidar system intended for atmospheric-sensing applications, which makes use of reference and signal waves possessing the MTC properties, is formulated for the first time.     

Femtosecond Laser Filamentation in Liquid Spray

Russian Physics Journal - The paper presents the femtosecond laser filamentation, which splits the liquid spray into two jets. The dependence is suggested for the acoustic signal and the...     

Ferromagnetic Resonance Spectra in Single-Crystal Hexagonal Ferrites

Theoretical and experimental studies of ferromagnetic resonance in single-crystal hexagonal ferrites with different types of magnetocrystalline anisotropy (axis and plane of easy magnetization) are reported. The ferromagnetic resonance is examined in the 12–38 GHz frequency range in the state of homogeneous magnetization and in the presence of a strip domain structure inherent in materials with an axis of easy magnetization. This comprehensive ferromagnetic resonance investigation is shown to allow determination of not only anisotropy fields and g-factors but also saturation magnetization of a material from testing one sample alone. The anisotropy of g-factor of Zn₂Y is found experimentally.     

A Study of Magnetic Crystallographic Anisotropy of Substituted Hexaferrites by the Method of Ferromagnetic Resonance

Russian Physics Journal -