We report the results of measuring the complex coupling coefficients in ring He – Ne lasers with a radiation wavelength of 632.8 nm. It is found that in assembling ring resonators from mirrors of the same quality, there is no correlation between the dissipative and conservative backscattering components. The analysis of the measurement results shows that this behaviour is associated with the speckle

We consider the issues of measuring the deformability of red blood cells by the method of laser diffractometry in shear flow (ektacytometry). The measurement procedure is optimised taking into account the finite resolution of the video recording system of the laser ektacytometer. An algorithm is proposed that allows one to determine with high accuracy the diffraction pattern parameters necessary for

Two-dimensional optical image edge enhancement is investigated using a spatial acousto-optical (AO) filter operating at two wavelengths of optical radiation, which significantly increases the reliability of measurements and also reduces the effect of noise. The filter operates basing on diffraction of light in two diffraction orders. It is shown that, in the general case, it is impossible to obtain

A configuration of a laser polarisation modulator based on isotropic acousto-optic interaction is proposed. Polarisation control is performed by a 2D acousto-optic cell based on one monoclinic single crystal. A possibility of implementing this modulator on the basis of a KY(WO4)2 crystal is demonstrated.

A method for obtaining non-Gaussian light beams with azimuthal field polarisation in a waveguide quasi-optical cavity is described. The method is based on the employment of polarisation-selective diffraction structures as laser mirrors. Efficient excitation of such beams at the output from an optically pumped waveguide HCOOH laser (λ = 0.4326 mm) with an inhomogeneous reflecting input and semitransparent

Indirect drive thermonuclear targets with fuel capsules at the stage of X-ray irradiation in a free flight are proposed. The absence of structural elements fixing the fuel capsule at the beginning of this stage will make the initiation of their associated instabilities impossible and will thereby improve the fuel compression.

Generation of coherent radiation in the IR and terahertz ranges during the propagation of a multi-terawatt laser pulse along a nanowire target is investigated. In the process of interaction, dense electron bunches are displaced from the target and accelerated in the laser field, generating intense electromagnetic radiation. Three regimes of interaction can be realised depending on the duration and

Nanosecond laser ablation of a bulk gold target in a melt of a sodium nitrate salt is investigated. It is shown that the form of plasma plumes on the target surface during ablation depends on the laser beam scan rate. The extinction spectra of sodium nitrate composites with gold nanoparticles during solidification is analysed.

The selectivity of laser photoionisation of 177mLu nuclear isomer with respect to natural isotopes has been studied for the first time using a three-stage lutetium photoionisation scheme .

We report a study of the effect of postgrowth treatment of ZnGeP2 single crystals (low-temperature annealing, irradiation with fast electrons, polishing of working surfaces) and the conditions of exposure to repetitively pulsed laser radiation [wavelength (2091 or 1064 nm), pulse repetition rate, beam diameter, exposure time, sample temperature] on the laser-induced damage threshold (LIDT) of the surfaces

Using an improved travelling wave model, we have numerically investigated the dynamics of a Q-switched bismuth-doped fibre laser. Comparison of simulation results with previously reported experimental data demonstrates good agreement of the multipeak lasing structure and the shape of the strongest pulses at various levels of pumping. We have assessed the effect of the main laser parameters on output

We study the conditions of frequency modulation, spectral broadening, and amplification of a Gaussian pulse – a whispering-gallery-mode (WGM) wave packet (WP) – propagating along a spiral trajectory on the surface of an active cylindrical optical waveguide, in which a travelling refractive-index wave (TRIW) is generated. Analytical expressions are obtained for the dependences of the duration, chirp

Operation of a tunable tandem-type low-coherence light source with high spectral brightness based on commercially available optical elements (superluminescent diode, semiconductor optical amplifier, and bulk dwiffraction grating) is studied experimentally. A unique combination of the output source characteristics, namely, a spectral power density of 36 mW nm−1, a wavelength tuning range of 35 nm (834

Semiconductor lasers based on AlGaInAs/InP heterostructures with ultra-narrow and asymmetric waveguides are comparatively studied. It is shown that the use of these waveguides with a simultaneous increase in the quantum well depth makes it possible to increase output powers. Such lasers based on both strongly asymmetric and ultra-narrow waveguides with a stripe contact width of 100 μm demonstrate an

We report the results of theoretical and experimental studies of a digital system for regulating and stabilising the frequency of a four-frequency Zeeman laser gyroscope (ZLG), in which generation occurs simultaneously on two longitudinal modes with orthogonal circular polarisations; therefore, four light waves propagate in the optical ring resonator. In contrast to a two-frequency Zeeman laser gyroscope

A high degree of cross-correlation of radiation wavefront aberrations, measured from a point reference source and from an extended object (a system of several luminous points), has been for the first time revealed based on simultaneous measurements of phase fluctuations in optical waves propagating in a turbulent atmosphere. The experimental data are consistent with analytical calculations. The high

We have developed and experimentally implemented an adaptive laser vector-phase hydroacoustic measuring system, which allows one to determine the total acoustic intensity vector. A receiving element of the measuring system comprises six spatially separated fibre-optic coil-type sensors. Signals from the sensors are phase demodulated by using a six-channel adaptive holographic interferometer based on

We report the results of theoretical and experimental studies of noise in a delay-line optoelectronic microwave oscillator with optical gain. The effect of various noise sources on the parameters of an optoelectronic microwave oscillator is considered, and, in addition to the noise of its individual components, several linear and nonlinear mechanisms for converting optical carrier noise into microwave

We present the design and results of studying the characteristics of an optoelectronic microwave oscillator in the free-running regime are presented, propose a method for synchronising it with a signal of a highly stable crystal oscillator using a phase-locked loop, and analyse the results of an experimental study on the frequency instability of an optoelectronic microwave reference oscillator. The

We report a theoretical analysis of the spectral properties of atoms localised in an optical pulsed trap. It is shown that this analysis can be carried out using the correlation coefficient calculated from the averaged dynamics of atomic excitation by resonant probe laser light in the presence of a nonresonant pulsed field. It follows from calculations that at a laser pulse duration of 8 ps, atoms

We have proposed a new design of microstructured optical fibres (MOFs), containing three rings of identical circular holes around a core, with different separations between the rings. The properties of the MOFs have been analysed numerically using the finite element method (FEM), and the leakage loss in the spectral range 0.40 – 2.65 μm has been calculated for the fundamental and higher order modes

The results of spectral diagnostics of an optical discharge (OD) plasma propagating through a hollow-core revolver fibre under the action of repetitively pulsed laser radiation are presented. The revolver fibre is made of silica glass, with a diameter of the hollow core being 20 μm. The peak values of the laser radiation intensity reach 1012 W cm−2at an average Nd : YAG laser power of about 2 W. The

To raise the stimulated Brillouin scattering (SBS) threshold, we have fabricated an optical fibre having a core heavily doped with germanium oxide and displaced from the fibre axis. A method has been proposed for broadening the SBS gain spectrum of the fibre by winding it onto a small-diameter spool, and a broadening of the spectrum by 5.4 dB has been demonstrated, which indicates an increase in SBS

We describe an experiment on the interaction of a dipolar magnetic field with the laser plasma flow produced inside of a laboratory magnetosphere. This interaction is found to exhibit two dynamic stages: after a prompt displacement of the dipole field by the laser plasma, the magnetic field is captured and carried outside of the magnetosphere. The resultant data confirm the results of previous measurements

The SRS process in the regime of nonlinear phase modulation of laser and Stokes radiation waves is studied experimentally. The effect of the relationship between the laser and Stokes wavelengths on the value of the minimum laser pulse duration, at which an efficient SRS process is possible, is ascertained. The possibility of obtaining maximally broadband Stokes radiation pulses by matching the group

The nonlinear optical responses of perovskite films CsPbI2Br, MAPbI3 + 1% PVC, MA0.15FA0.75Cs0.1PbI2.85Br0.15, and MA0.15FA0.75Cs0.1PbI3, irradiated by femtosecond laser pulses with wavelengths of 1064 and 532 nm, are investigated using z-scan measurements. Nonlinear absorption is found to occur in perovskite films irradiated at a wavelength of 1064 nm; the nonlinear absorption coefficient in thin

The features of spontaneous and stimulated emission of polyfluorenes, polyvinylcarbazole, and low-molecular-weight electron-donor compounds incorporated into various materials are studied in the presence of nitrotoluene vapour. Lasing in planar thin-film waveguides is achieved. The dynamics of the lasing spectra of a thin-film optical chemical sensor is presented. It is shown that the response time

A GaSb/GaAsBi type-II quantum dot structure is proposed for fabricating middle-wave infrared (MWIR) and long-wave infrared (LWIR) lasers. The finite element method is employed to investigate the train distributions and band structures of the proposed structures with different Bi contents and QD sizes. It is found that the strain component εxx decreases with Bi contents and heights, and increases with

We report an analysis of attained output powers of laser diode bars (LDBs) and power densities of two-dimensional laser diode arrays (LDAs). A new LDA design is proposed and its thermal regime is simulated. The cw output power of the proposed LDA consisting of standard cw LDBs (output power 100 W, efficiency 50%, cavity length 2 mm) can reach 5 kW cm−2. The parameters of a coolant flow in the microchannels

We consider interference fluxes of energy, momentum and angular momentum, describing the interaction of electric charges with constant and variable electromagnetic fields. Absorption and stimulated emission of atoms in the field of free and evanescent waves are described. It is shown that in the case of interaction with reactive fields, the momentum of an atom during absorption and stimulated emission

The changes in the optical properties of water and hexane under femtosecond irradiation (Ti : Al2O3 laser, wavelength 800 nm, intensity ∼1013 W cm−2) are investigated in the cavitation (bubble-formation) regime using interference microscopy in a time interval of ∼1.5 ns since the impact onset. A comparison of the dynamics of radiation-induced processes (solvation of excess electrons, pair recombination

We report a computational and experimental study of the possibility of replacing NF3 nitrogen trifluoride, which is used in the NF3 – D2 – He fuel composition in the atomic fluorine generator of a supersonic cw chemical HF laser, with N2F4 tetrafluorohydrazine. As a result of comparing the specific energy characteristics of an HF laser operating with each of the oxidisers, it is shown that the replacement

Pulsed radiative characteristics of high-power semiconductor lasers based on an asymmetric InGaAs/AlGaAs/GaAs heterostructure with an active region including two quantum wells and a gradient waveguide on the side of the p-emitter are studied. It is shown that the use of the proposed design allows efficient laser operation under pumping by 100-ns current pulses in the temperature range 25 – 90 C. The

We investigate skin optical clearing in laboratory animals ex vivo and in vivo by means of low-molecular-weight paramagnetic contrast agents used in magnetic resonance imaging (MRI) and a radiopaque agent used in computed tomography (CT) to increase the sounding depth and image contrast in the methods of fluorescence laser imaging and optical coherence tomography (OCT). The diffusion coefficients of

Semiconductor lasers based on AlGaInAs/InP heterostructures with a strongly asymmetric waveguide are studied. It is shown that the use of such a waveguide simultaneously with an increased quantum well energy depth provides conditions for increasing the output laser power. The semiconductor AlGaInAs/InP lasers based on a strongly asymmetric waveguide with a stripe contact width of 100 μm demonstrated

We report a technique for studying the absorption of optical radiation in layers of a semiconductor heterostructure by the method of probe radiation coupling. The studies are carried out using specially made isotype samples based on AlGaAs/GaAs, simulating an n-type doped laser waveguide with a concentration of 1017 – 1018cm−3. The main features of the experimental setup and calculation methods are

The possibility of amplifying a THz hybrid surface plasmon in a structure with an Hg0.82Cd0.18Te epitaxial film grown on a GaAs substrate and covered with a metal layer is investigated. It is shown that for a film thickness of 100 nm and a temperature of 80 K, the hybrid surface plasmon mode gain can be greater than external losses at a pump radiation intensity with a wavelength of 2.3 μm, exceeding

For a neodymium glass laser, which is used to pump the parametric amplifier of the PEARL facility, we investigate the problem of filling the pinholes of vacuum spatial filters with plasma resulting from the ablation of the pinhole surface by laser radiation. The time of plasma expansion is measured and the causes of its appearance are determined, among which the main ones are the spherical aberrations

The dynamics of frequency-modulated pulses in fibres with sequentially inscribed refractive-index gratings having a different period is considered. It is shown that the proposed structure of the fibre can be used to generate picosecond and subpicosecond pulses with peak powers on the order of 1 MW.

Based on the combined use of polymerisable polyacrylamide, collagen and an aqueous solution of Flavin adenine dinucleotide (FAD), we have developed a new technique for fabrication of composite phantoms mimicking fluorescence properties of human skin. A comparative analysis of the absorption and scattering coefficients, refractive indices, as well as fluorescence spectra of phantoms with different concentrations

Laser characteristics of continuous-wave (cw) and passively Q-switched Nd : LGGG lasers based on the 4F3/2 → 4I13/2 transition of an neodymium ion are investigated. The lasing spectra of the cw and the Q-switching regimes are studied in detail. The thermal optical coefficient for the Nd : LGGG crystal at a wavelength of 1.33 μm is estimated to be 15.3 10−6 K−1. By inserting a quartz plate at the Brewster

Sawtooth two-layer microstructures with internal and external, as well as with two internal reliefs, composed of technological and commercially available optical plastics or an optical plastic and nanocomposite material are investigated. By using the corresponding model microstructures in the frameworks of the rigorous diffraction theory, the limiting spectral and angular characteristics are estimated

Analytical expression for the fluorescence response of a photosensitiser uniformly distributed in the superficial layer of biotissue is obtained in the diffusion approximation of radiative transfer theory, and the approach for estimating the fluorescent layer thickness based on dual-wavelength excitation of fluorescence is proposed. It is shown that the error in estimation of the fluorescent layer

The efficiency of electric pumping of THz quantum-cascade lasers (QCLs) with strip geometry is studied depending on the number and position of contact pads. The numerical simulation of the electric potential distribution in the THz QCL active region is used to determine the required thicknesses of the upper metallisation layers of the THz QCLs to minimize the voltage drop along the laser structure

It has been shown experimentally and confirmed by numerical simulation that strong local stretching of sensing fibre distorts the signal detected by a phase-sensitive optical time-domain reflectometer (OTDR) from the fibre section behind the local disturbance region. Comparison of experimental data with theoretical estimates and numerical simulation results leads us to conclude that the physical mechanism

The first issue of the Quantum Electronics journal for 2021 is dedicated to laser biophotonics and features primarily the papers based on invited reports delivered at the International Symposium 'Optics and Biophotonics 2020' (https://sfmconference. org/files/20-sfm-program-5-10-20-total.pdf), which is part of the famous international conference Saratov Fall Meeting (SFM) held annually in Saratov (Russia)

The dynamics of the formation and relaxation of microbubbles in a polyacrylamide phantom of tattooed skin under the action of a series of laser pulses with 15-ns duration is studied. It is shown that the growth of microbubbles occurs within a few milliseconds, and their lifetime varies from several seconds to several hours, depending on the water content in the phantom and the fluence (energy density)

A new method is proposed to increase the spectral resolving power of collinear acousto-optical filters by using optical feedback when the light leaving the region of its interaction with a periodic structure formed in the crystal by an acoustic wave returns to the input of the crystal, in which the diffraction process repeats itself many times. The light beam returned to the interaction region changes

The paper describes the design of an optical coherence tomograph adapted for studying the state of the tympanic cavity of the human middle ear. We present the images obtained by the method of optical coherence tomography, which are characteristic of the norm and of the case of pathology – otitis media with effusion.

The possibility of increasing the efficiency of light action during scleral collagen riboflavin/UV photocrosslinking by means of immersion clearing of tissue before UV irradiation is studied. The effectiveness of photo-action is assessed by a decrease in the relative content of the photocrosslinking sensitizer, riboflavin, which is determined from the decay times of tissue fluorescence at different

We report a fast and computationally stable method for computer simulation of optical properties of layered scattering systems containing luminescent layers. The method is based on the solution of one-dimensional scalar radiative transfer equations and makes it possible to calculate spectral and angular characteristics of luminescent radiation emerging from the system under various conditions of luminescence

The results of measuring the derivative of the pulse wave using a laser autodyne based on the Fourier analysis of the low-frequency spectrum of the interference signal are presented. The features of using the windowed Fourier transform for window types and window widths are discussed. The correlation coefficient between the derivative obtained by direct differentiation of the sphygmographic signal

Water plays an important role for normal functioning of the skin. The stratum corneum (SC) – the outermost layer of the epidermis – maintains the skin barrier function and regulates the water balance in the organism. Water is non-homogeneously distributed in the SC and its correct determination is important in dermatology and cosmetology. Confocal Raman microspectroscopy (CRM) is the most suitable

A scheme is proposed for measuring electron level populations in a semiconductor quantum dot embedded in a multimode waveguide. The photon transmittance of the waveguide under steady-state pumping is shown to depend on the presence of an electron in the ground state of the quantum dot. The influence of waveguide, quantum dot, and photon source parameters on the electron detection process is examined

The possibility of using bursts of microsecond pulses of an Yb,Er : glass laser (λ = 1.54 μm) for cataract destruction was investigated experimentally in vitro for the first time. The energy in a laser pulse was limited from below by the eye lens destruction threshold and from above by the radiation resistance of the input end face of the radiation-supplying fibre. The energy of a burst consisting

We report a theoretical study of plasmon generation of a giant electromagnetic field in a supernarrow nanoslit formed by a silver cylinder and a flat mirror surface. It is shown that as the silver surfaces approach each other, gap plasmons are excited in the gap between them, which results in a resonant amplification of the field. It is demonstrated for the first time that the electric field amplification

The results of numerical simulation of the near-field distribution inside and in the vicinity of two types of gold nanoparticles (nanospheres and nanorods) intended for producing complexes of gold nanoparticles linked with proteins and exciting photosensitizers in the wavelength range of 532 – 770 nm are presented. Quantitative estimates of the field localisation (enhancement) are obtained depending

An action of the IR laser pulses with a wavelength of 1.56 μm, moderate intensity, and various durations on a collagen framework structure and sclera tissue permeability is considered. It is shown that the temperature thresholds of collagen denaturation in tissues under the laser irradiation are substantially lower as compared to those under conventional homogeneous heating in a calorimeter oven. A

The efficiency of using silicon nanoparticles, produced by laser ablation of porous silicon in liquids, as agents for hyperthermia of tumours using laser radiation with wavelengths of 633 and 800 nm is evaluated. Using the optical parameters of the nanoparticles suspensions determined earlier by the spectrophotometry measurements, the heating of tumour tissue with embedded nanoparticles is numerically

The results of the operation of a wavefront correction system based on a deformable bimorph mirror of the PEARL subpetawatt laser facility are presented. An improvement in the quality of focusing of laser radiation, which led to an increase in the Strehl ratio from 0.3 to 0.6, is demonstrated. The features of the compensation for phase distortions of the wavefront in the case of a low pulse repetition