An Erratum to this paper has been published: https://doi.org/10.1134/S0018151X23010224

Coherent Doppler lidars are traditionally used to measure wind speed in the atmospheric boundary layer. However, in addition to wind speed data, coherent Doppler lidars are a source of information on the distribution of the aerosol particle concentration in the atmosphere, which makes it possible to measure the height of the planetary boundary layer, to determine the cloud base and the number of cloud layers, as well as information on the distribution of aerosols along the path or in the scanning sector. The paper considers algorithms for processing data from coherent Doppler lidars to obtain comprehensive information about the parameters of the atmospheric boundary layer. The results of experimental studies and their analysis are presented.

The comparison of the influence of intra-cavity spectral selectors: static Bragg gratings and dynamic gain gratings, has been presented. It has been shown that their effect on the spectral properties of the laser radiation with a loop resonator is similar. The performed statistical study of the mode composition of the groups of the generation pulses at the Q-factor modulation mode allows us to conclude that the rewriting of the grating by the subsequent group pulse does not prevent radiation at the same frequency. This opens up the possibility of frequency stabilization of the radiation. The presence of an intra-cavity Bragg grating causes an increase in the probability of preserving the radiation frequency in neighboring pulses of the radiation group. It has been shown that there is a narrowing of the pulse generation spectrum in the group, despite the fact that the spectral width of the grating exceeds the spectral width of the generation pulse. The combined operation of static and dynamic intra-cavity gratings makes it possible to create a line of lasers with high pulse energy, radiation quality close to the diffraction limit, high peak power, and a narrow radiation spectrum.

Subject of study. A digital holographic system for layer-by-layer control of component quality in additive manufacturing able to determine the size and depth of defects on the surface of each layer was investigated. Method. The digital holographic system for layer-by-layer control of component quality in additive manufacturing operates based on a two-wavelength holographic interferometry method. The digital holographic system is based on a Michelson interferometer. The considered method involves recording holograms of the surface of each component layer at two adjacent wavelengths. As a result of hologram reconstruction, the complex amplitudes of the object wave in the reconstruction plane are determined, which, in turn, define the phases of the waves and their difference. The wave phase difference allows the depth of the defect on the component layer surface to be determined. A tunable diode laser and camera based on a CCD matrix are used as the radiation source and detector, respectively. Main results. The results of the investigation of the surfaces of additively manufactured components using the two-wavelength holographic interferometry method are presented. The recognition of large irregularities is possible through expansion of the phase pattern. The detection of surface defects with the size of 25 mu m is demonstrated. The reconstructed surface of a component manufactured by laser sintering of successive layers using the M250 additive setup for selective laser sintering and the reconstructed surface of a millimeter-scale macroscopic object are presented. Practical significance. The possible use of the digital holographic system for component quality control in industrial settings, including those applying additive technologies, is demonstrated. The component quality criterion is the absence of defects (cavities or protrusions) with size larger than 25 mu m. (C) 2022 Optica Publishing Group

Subject of study. The lasing spectra of a pulsed laser based on a Cr:LiSrAlF6 active medium are studied. Method. An intracavity transmission volume Bragg grating was used as the lasing mode on two aliquant wavelengths and wavelength tuning. The grating was recorded in a photo-thermo-refractive glass. Main results. For the first time in Russia, simultaneous narrowband lasing was demonstrated at two aliquant wavelengths in the band of 795-895 nm in a Cr:LiSrAlF6 crystal. The use of a volume transmission Bragg grating for continuous tuning of the central wavelength of the generated laser emission was demonstrated using additional feedback through a mirror with a high reflection coefficient positioned in the first diffraction order. Practical significance. Pulsed lasers with tunable wavelengths are applied in various scientific and practical applications including ecological monitoring of atmosphere conditions. The lasing at two aliquant wavelengths investigated in this study enables the design of high-power pulsed sources of terahertz radiation in the range of 15.5-27.1 THz. (C) 2022 Optica Publishing Group

Селективное лазерное сплавление (СЛС) является перспективным направлением аддитивных технологий. Проблема контроля микроструктуры и качества конечного изделия, получаемая методом СЛС, решается подбором режимов плавления с помощью экспериментального поиска или численного моделирования. На сегодняшний день сформировалась многоуровневая методология моделирования СЛС-процессов, которая и рассматривается в настоящей работе.

Средства дистанционного зондирования атмосферы в оптическом и радиочастотном диапазонах находят широкое применение в аэронавигации, технологиях обеспечения безопасности полетов, метеорологии, экологии, климатологии и в иных сферах. Лидарные и радиолокационные системы имеют общие принципы функционирования. Несмотря на эту общность, их традиционно разделяют в зависимости от используемого частотного диапазона электромагнитного излучения. Следствием такого разделения становится разделение их функциональных возможностей и решаемых задач. Однако, как показывает практика, комплексное использование оптического и радиочастотного излучения при атмосферном мониторинге может привести к синергетическому эффекту и существенному расширению возможностей подобных системы. В статье рассматриваются возможности и перспективы совместного применения оптико-­радиочастотных средств атмосферного зондирования.

Приведено сопоставление влияния внутрирезонаторных спектральных селекторов: статических решeток Брэгга и динамических решeток коэффициента усиления. Показано, что их влияние на спектральные свойства излучения лазера с петлевым резонатором аналогично. Проведенное статистическое исследование модового состава цугов импульсов генерации в режиме модуляции добротности позволяет сделать заключение о том, что перезапись решeтки последующим импульсом цуга не препятствует излучению на той же частоте. Это открывает возможность частотной стабилизации излучения. Наличие внутрирезонаторной решeтки Брэгга приводит к повышению вероятности сохранения частоты излучения в соседних импульсах цуга излучения. Показано, что наблюдается сужение спектра генерации импульса в цуге несмотря на то, что спектральная ширина решeтки превышает спектральную ширину импульса генерации. Совместная работа статических и динамических внутрирезонаторных решeток позволяет создать линейку лазеров с высокой энергией в импульсе, качеством излучения, близким к дифракционному пределу, высокой пиковой мощностью и узким спектром излучения. Ключевые слова: стационарная решeтка, динамическая решeтка, дифракционная эффективность, самонакачивающийся резонатор, обращение волнового фронта.

Сверхзвуковые газовые и химические лазеры являются источниками мощного непрерывного излучения с высоким оптическим качеством. Эти качества позволяет использовать такие лазеры в составе автономных мобильных комплексов. Представлен краткий обзор работ по созданию и совершенствованию лазеров, формированию высококачественного излучения, разработки перспективных систем хранения и подготовки рабочего тела, систем восстановления давления.

The influence of reflective Bragg gratings that are formed in an active medium due to the spatial periodic modulation of gain on the spectral properties of lasing are investigated by an example of a pulsed Nd :YAG laser. It is shown that, at a certain choice of the formation regime of reflective gratings of gain, the lasing bandwidth can be reduced by a factor of 3-5, with a corresponding increase in the pulse energy and significant improvement of spatial beam quality.

Combination of combustion-driven gas-dynamic lasers with gas-turbine turbojet and turbo-shaft engines has been considered. Development of aviation technologies has been analyzed. Output performance of a laser taking air from modern helicopter and airplane engines taking into account ensuring exhaust of spent active medium into the ambient atmosphere has been determined. The application of penetration cooling of the laser nozzle bank blades has been evaluated.

Дистанционное зондирование атмосферы в оптическом диапазоне в настоящее время является одним из наиболее эффективных способов получения информации о ее физико-­химических и динамических характеристиках. Сегодня лидарные системы атмосферного мониторинга широко применяются в метеорологии, экологии, климатологии, в сфере обеспечения безопасности полетов, ветроэнергетике. В статье описываются физические принципы функционирования атмосферных лидаров, приводятся результаты измерений и технические характеристики лидарных метеосистем и комплексов отечественной разработки, выпускаемых серийно.

This article is devoted to the simulation of the processes of formation of dust clouds in the absence of gravitation, which is necessary for understanding the processes proceeding in dust clusters in outer space, upper planetary atmosphere, and on the surface of space objects, as well as for evaluating the possibilities of creating disperse structures with given properties. The chief aim of the simulation is to determine the general laws of the dynamics of the dust cloud at the initial stage of its formation. With the use of the original approach based on the particle-in-cell method that permits investigating the mechanics of large ensembles of particles on contemporary computational platforms, we consider the mechanics of a dusty medium in the process of its excitation in a closed container due to the vibration of the walls, and then in the process of particle scattering when the container opens in outer space. The main formation mechanisms of a dust formation have been elucidated, and the possibilities of mathematical simulation for predicting spatial and time characteristics of disperse structures have been shown.

A high-power compact repetitively pulsed Nd:YAG laser with transverse diode pumping and multiloop self-pumped phase-conjugate cavity is proposed. Pulse trains with an energy of 1.5 J and beam quality parameter of M 2 ≤ 1.2 are generated at a divergence of 0.4 mrad and luminance of 5 × 1014 W/(cm2 sr). The peak power of single-frequency pulses is greater than 15 MW at an energy of 170 mJ and a laser bandwidth of 300 MHz.

Поступило в Редакцию 6 июля 2016 г.В окончательной редакции 29 декабря 2016 г

The results of the first measurements in Russia of the vortex wakes left by different types of airplanes with the aid of 1.5-μm range home-made commercially manufactured coherent Doppler lidars are presented. The characteristic features of the measurement of vortex wakes by such lidars are considered. The dynamics of the vortex wake left by a Boeing 737-800 is shown.

Problems of increasing the efficiency and the functionality of complex optoelectronic systems for monitoring real atmospheric conditions and of their use are discussed. It is shown by the example of a meteorological complex comprising an infrared wind-sensing lidar and an X-range Doppler radar that the complexation of probing systems working in different electromagnetic-radiation ranges opens up new opportunities for determining the meteorological parameters of a turbulent atmosphere and investigating the interaction of radiation with it.

A compact, pulsed-periodic YAG: Nd3+ laser with self-pumped phase-conjugate multiloop cavity and passive Q-switching by YAG: Cr4+ and GSGG: Cr4+ crystals has been studied. It is established that the energy and temporal parameters of radiation in separate pulses of a periodic train can be controlled almost without changing the pulse train energy. A regime of generating modulated radiation pulses with a peak power of up to 30 MW and a spatial brightness of 1.7 × 1015 W/(cm2 sr) at a radiation beam quality parameter of M 2 < 1.2 has been realized in experiment.

The generation regimes in a pulsed Nd:YAG laser with transverse LED pumping and multiloop self-pumped phase-conjugate cavity on the gain gratings are studied. The differential efficiency of laser is 27% in the free-running regime at a pulse energy of up to 1 J and quality parameter M 2 of no greater than 1.5. The pulse energy under passive Q -switching is no less than 60% of the pulse energy in the free-running regime at the same beam quality. The generation of the narrow-band radiation is demonstrated. A generation band of no greater than 1.2 GHz corresponds to the primary single-frequency high-power laser pulse in the free-running mode under conditions for self- Q -switching on the gain gratings. When additional elements (F 2 − :LiF and Cr 4+ :YAG crystals) are introduced in the optical scheme of the phase-conjugate cavity, similar narrowband single-mode generation is observed in the passive Q -switching regime as a pulse train or monopulse. The laser pulse power is up to 2 MW at a pulse duration of 20 ns.