Метод лазерной фрагментации/лазерно-индуцированной флуоресценции (ЛФ/ЛИФ) хорошо известен своей эффективностью для обнаружения сложных химических соединений по сигналам флуоресценции их характеристических фрагментов. Этот метод применяют, например, для измерения локального содержания азотистой кислоты и гидроксильных радикалов в атмосфере, визуализации промежуточных стадий процессов горения, дистанционного обнаружения веществ в газообразном состоянии в атмосфере и конденсированном состоянии на поверхностях и др. Впервые представлены результаты экспериментального исследования возможности дистанционного возбуждения ЛИФ характеристических фотофрагментов вещества в аэрозольном состоянии в атмосфере. Исследуемое вещество – фосфорорганическое соединение триэтилфосфат (ТЭФ). Показано, что синхронизированное двухимпульсное лазерное воздействие на аэрозольные частицы ТЭФ и их PO-фрагменты (молекулы оксида фосфора) позволяет примерно в семь раз повысить эффективность ЛФ/ЛИФ по сравнению с одноимпульсным лазерным воздействием. Установлено, что образование PO-фрагментов ТЭФ в аэрозольном состоянии под действием лазерного излучения с длиной волны 266 нм имеет спадающий экспоненциальный характер с постоянной времени 192,6 ± 20,2 нс. По характеру временной зависимости образования фотофрагментов полученные результаты принципиально отличаются от подобных измерений для других соединений в газообразном и конденсированном состояниях. The laser fragmentation/laser-induced fluorescence (LF/LIF) method is well known for its efficiency in detecting complex chemical compounds based on the fluorescence of their characteristic fragments. The method is applied, for example, to measuring the local content of nitrous acid and hydroxyl radicals in the atmosphere, visualization of intermediate stages of combustion processes, remote detection of substances in the gaseous state in the atmosphere and condensed state on surfaces, etc. We present for the first time the results of the experimental study of a possibility of remote excitation of LIF of characteristic photofragments of a substance in an aerosol state in the atmosphere. The organophosphorus compound triethyl phosphate (TEP) was used as the test substance. It has been shown that synchronized two-pulse laser irradiation of TEP aerosol particles and their PO-fragments (phosphorus oxide molecules) makes it possible to increase the efficiency of the LF/LIF process by approximately seven times compared to single-pulse laser exposure. It has been established that the process of formation of PO-fragments of TEP aerosol under the laser irradiation at a wavelength of 266 nm has a decaying exponential character with a characteristic time of 192.6 ± 20.2 ns. In terms of the nature of the time dependence of the formation of photofragments, the results obtained are fundamentally different from similar measurements for other compounds in gaseous and condensed states and motivate further research that will contribute to the development of the LF/LIF method.

This paper presents the results of an experimental study of the dynamic characteristics of the process of laser fragmentation/laser-induced fluorescence (LF/LIF) of trinitrotoluene traces on a paper surface under synchronized double-pulse laser irradiation. An Nd:YAG-laser (266 nm) was used for the fragmentation of TNT molecules, while fluorescence excitation of their NO fragments was performed using a KrF laser with a generation line of 247.867 nm in the region of the location of the bandhead of the P12 branch of the γ(0, 2) absorption band of the NO molecule. It was shown that the dissociation process of TNT traces has an inertial character and continues after the cessation of the fragmenting laser pulse. It was found that with the delay values between the fragmenting and probing laser pulses in the region of 200 ns, the efficiency of the LF/LIF method can be increased by 12 times. This paper presents the results of an experimental evaluation of the efficiency of two-pulse LF/LIF compared to single-pulse laser exposure, where the fragmentation of TNT molecules and excitation of their NO fragments were simultaneously performed by KrF laser pulses. The possibility of multiple increases in the efficiency of two-pulse LF/LIF with an increase in the energy density of the fragmenting laser radiation was shown. The obtained results are important in terms of increasing the sensitivity and/or range of the LF/LIF method for remote detection of traces of nitrocompounds.

A technique for parallel recording of lidar signals in the photon counting and charge accumulation modes at the Siberian Lidar Station (SLS) of the Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, is described in detail. A device for signal detection at the unique SLS lidar with the use of the combined technique is designed and experimentally tested. During the experimental testing of the device, the limits of applicability of the suggested technique to atmospheric temperature vertical profiling based on lidar signals of pure rotational Raman spectra are determined. The comparison between the lidar and satellite measurements shows their good agreement, which proves the high efficiency of the combined technique and confirms a possibility of atmospheric temperature profiling based on the SLS primary mirror throughout the altitude range of the SLS Raman lidar.

The efficiency of ten sodium atom excitation schemes that can potentially be used to generate a sodium polychromatic laser guide star (PLGS) and a monochromatic laser guide star (LGS) is compared. It is shown that for creating an LGS in sodium vapor using the cascade fluorescence effect with single-photon excitation, the most suitable is the 42P3/2 ← 32S1/2 transition excited at a wavelength of 330.237 nm and demonstrating the highest LGS characteristics, while the efficiency decreases by two orders of magnitude compared to a monochromatic LGS at a wavelength of 588.995 nm.

An original technique is suggested for pumping a pulsed CO2 laser by a longitudinal discharge in an alternating magnetic field. A small CO2 laser with active medium ∼200 mm long, pulse energy of ∼30 mJ, and efficiency of 3.4

This paper presents the results of an experimental study of the possibility of remote visualization of traces of some nitro-group-containing explosives (TNT, RDX, HMX, Composition-B, and Tetryl) on the surface of aluminum foil using the laser fragmentation/laser-induced fluorescence (LF/LIF) method. A tunable excimer KrF laser with a narrow generation line was used to fragment explosives and excite fluorescence of their NO fragments (nitric oxide molecules) from the second vibrationally excited state (v″ = 2). When recording optical responses, spectral selection of the γ(0, 0) fluorescence band of NO was carried out. The LF/LIF method is shown to be promising for creating scanning detectors that will allow remote detection of trace amounts of explosives with a concentration of up to 1 μg/cm2 on the surfaces of objects at a distance of several meters and simultaneously determine their location. The sensitivity of the one-color LF/LIF detection method can be increased by increasing the energy density of the probing radiation and/or by optimizing the LF/LIF excitation process.

Seven possible variants of the sodium atom excitation are considered for creating a polychromatic laser guide star (LGS). It has been shown that the 42P3/2 ← 32S1/2 transition excited at a wavelength of 330.237 nm is most suitable for creating a polychromatic LGS in sodium vapor using the effect of cascade fluorescence at one-photon excitation. In this case, the excitation efficiency will be 2 orders of magnitude lower compared to the efficiency of creating a monochromatic LGS at a wavelength of 589 nm.

— The limiting sensitivity of a technique for detecting vapors of nitrocompounds in the atmosphere based on laser fragmentation/laser-induced fluorescence is estimated in calculations with the developed kinetic model of the LF/LIF process. The calculations take into account the influence of atmospheric nitrogen dioxide as a limiting factor of the sensitivity of the technique in a real atmosphere. It is shown that if the concentration of nitrogen dioxide in the atmosphere does not exceed 10 ppb, the minimum detectable concentrations of nitrobenzene and o -nitrotoluene vapors are the ppb-level. It is also shown that the one-color excitation technique usually used for the detection of nitrocompounds does not allow attaining the maximal LF/LIF efficiency.

We present a mathematical model of the process of laser-induced fluorescence of phosphorus oxide (PO) molecules. Based on the model, the dependences of the fluorescence intensity of PO molecules on the energy and time parameters of exciting laser radiation are derived. It is ascertained that the dependence of the PO fluorescence signal on the energy density of the exciting radiation is a saturation curve, and the dependence on the pulse duration under real atmospheric conditions has a local maximum. It is shown that the optimal pulse duration decreases with the exciting radiation energy density.

The paper presents results of experimental study of the dynamics of laser-induced fragmentation of nitrobenzene molecules. It has been shown that when two laser pulses interacting with nitrocompound molecules and their decay products (NO fragments) are time delayed, it is possible to increase the sensitivity of the method of laser fragmentation/laser-induced fluorescence by approximately an order of magnitude for an optimal time delay between the pulses.

The results of a study of the degradation of the cyclotrimethylenetrinitramine (RDX) traces carried in fingerprints depending on the fingerprint number are presented. The surface concentration of the trace was assessed using macrophotography in polarized light and by the method of laser fragmentation/laser-induced fluorescence. A technique for estimating the surface concentration of RDX traces in sweat-fat fingerprints based on pixel-by-pixel scanning of macrophotographs is described. The data of parallel experiments on remote laser detection of RDX particles in fingerprints are presented. A comparison shows that the results of the direct measurements of the total trace area are in good agreement with the LF/LIF response data.

Подробно описан метод параллельной регистрации лидарных сигналов - в режиме счета фотонов и режиме накопления заряда - на Сибирской лидарной станции (СЛС) Института оптики атмосферы им. В.Е. Зуева СО РАН. Изготовлен и экспериментально апробирован прибор, реализующий комбинированный метод регистрации лидарных сигналов на уникальном лидаре СЛС. В ходе экспериментальной апробации прибора определены допустимые пределы применения предложенного метода для регулярных измерений вертикального распределения температуры атмосферы на основе лидарных сигналов чисто вращательных спектров спонтанного комбинационного рассеяния (СКР). Сравнение результатов лидарных и спутниковых измерений показывает их хорошее согласие, что доказывает высокую эффективность применения комбинации режимов регистрации и подтверждает возможность получать вертикальное распределение температуры атмосферы с доверительным интервалом (погрешность измерений) 2-4° во всем диапазоне высот работы СКР-лидара СЛС на базе главного зеркала. A technique for parallel registration of lidar signals in photon counting and charge accumulation modes at the Siberian lidar station of Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences (SLS) is described in detail. A device is designed and experimentally tested for recording lidar signals with the use of the combined technique at the unique SLS lidar. During the experimental testing of the device, the limits of applicability of the technique suggested to regular measurements of the vertical distribution of air temperature based on lidar signals of purely rotational Raman spectra are determined. The comparison between the lidar and satellite measurements shows their good agreement, which proves the high efficiency of the combined technique and confirms the capability of deriving the vertical distribution of atmospheric temperature throughout the altitude range of the primary mirror of the Raman lidar of SLS.

Выполнен расчет колебательных и вращательных термов электронных состояний X2Π и B2Σ+ оксида фосфора (PO). Представлен расчетный спектр поглощения молекулы PO, соответствующий переходу B2Σ+ (vʹ = 0) – X2Π (vʺ = 0).

The paper presents the results of calculating the absorption spectrum of a phosphorus monoxide (PO) molecule corresponding to the A2Σ+(v'=0)-X2Π(v''=0) transition. The efficiency of excitation of the PO molecule is estimated as a function of the spectral parameters of the laser radiation. The positions of the fluorescence bands of PO are calculated. It is shown that the use of excitation wavelengths near the bandheads of the (P22+Q12) and P12 branches of the A2Σ+(v'=0)-X2Π3/2(v''=0) band provides spectral separation of the (0, 1) γ-band of the LIF of PO and vibrational-rotational Raman spectrum of atmospheric oxygen. The spectral responses of dimethyl methylphosphonate vapor in air under the action of KrF-laser radiation at a wavelength of 247.78 nm have been experimentally studied. In the wavelength range 252-260 nm, the (0, 1) γ-band of the LIF of PO-fragments and the vibrational-rotational band of spontaneous Raman scattering on oxygen molecules are unambiguously interpreted. It is shown that the results of calculations of the shape and position of the fluorescence spectra are in good agreement with the experimental data.

В работе представлены результаты оценки эффективности лазерного возбуждения молекул оксида фосфора в зависимости от спектральных параметров излучения.

The paper discusses the problem of ensuring the linearity of photo registration of the lidar signal of molecular scattering on the main lidar of the Siberian lidar station (SLS) based on a unique mirror with a diameter of 2.2 m. To reduce the dynamic range of signal changes, it is proposed to use a mechanical shutter based on a disk obturator to cut off the near zone of the lidar signal in the altitude range of 0÷30 km. A high-speed brushless motor was used as an obturator driver. The synchronization signal was generated by a Hall sensor. Bench and full-scale tests of the obturator were carried out. It is shown that the error of the Hall sensor does not affect the delay and duration of the shutter opening.

Показано, что определение значений порога дискриминатора для каждого модуля фотоэлектронного умножителя (ФЭУ)/канала счетчика фотонов позволит регистрировать лидарные сигналы в одинаковых условиях. Проведена стендовая апробация определения значений порогов дискриминатора счетчика фотонов «PHCOUNT4».

Results of calculation of the absorption spectrum of phosphorus oxide (PO) corresponding to the A2Σ+ (v′ = 0) − X 2Π (v′′ = 0) transition are presented. The calculation is performed taking into account the perturbation of the v′ = 0 level of the A2Σ+ state by the v′ = 4 level of the b4Σ− state. The efficiency of laser excitation of PO molecules is estimated as a function of the spectral parameters of the radiation. The time dependence of the efficiency of the excitation of PO fragments is calculated for a real atmosphere under two-pulse laser fragmentation of organophosphates for specified spectral linewidths Δλ and center positions λ0.

В работе обосновывается выбор крутизны спектральной характеристики интерферометра Фабри-Перо (ИФП) для некогерентного доплеровского лидара. Представлены результаты численного моделирования относительной чувствительности пропускания ИФП при изменении скорости ветра в атмосфере на 1 м/с для различных базах ИФП.