Представлена математическая модель процесса лазерного возбуждения молекулы оксида фосфора (PO) в электронное состояние B 2Σ + с последующей его релаксацией в условиях реальной атмосферы. На основе модели получены зависимости интенсивности β-системы полос флуоресценции молекул PO от энергетических и временных параметров возбуждающего лазерного излучения. Показано, что с уменьшением плотности энергии возбуждающего излучения происходит уменьшение оптимальной длительности импульсов. A mathematical model of the process of laser excitation of a phosphorus oxide (PO) molecule into the electronic state B2Σ+ with its subsequent relaxation in a real atmosphere is presented. Based on the model, the dependences of the intensity of the β-system of fluorescence bands of PO molecules on the energy and time parameters of exciting laser radiation are obtained. It is shown that with a decrease in the energy density of the exciting radiation, the optimal pulse duration decreases.

The work describes the system for spectral filtering of probing radiation for studying the dynamics of photofragments during double-pulse excitation of molecules by the LF/LIF method. The parameters of the special narrow-band excimer KrF laser used to excite laser-induced fluorescence of PO molecules are presented. Using the AvaSpec-3648 fiber-optic spectrometer installed in the transmission path of the KrF excimer laser radiation, an analysis of the spectral composition of the output laser radiation was carried out. Using the ZEMAX CAD system, the optical design of the system for spectral filtering of KrF laser probing radiation was calculated. Theoretical results of calculating the position of the probe narrow-band radiation beam at the edge of the gain of the KrF laser with a wavelength of 247.8 nm and the broadband spontaneous radiation of the KrF laser in the wavelength range 248.2–248.5 nm are presented. Experimental results for assessing the effectiveness of the spectral filtering unit for probing radiation based on the spatial separation of the spectral components contained in the output radiation in a controlled region of space are presented.

Development of laser technologies increases requirements for lasers being developed which generate narrow-band radiation at different wavelengths. In view of this, the importance of wavelength-tunable diode and vibronic lasers with broadband amplification circuits increases. A possibility of generating highly coherent radiation in a solid-state alexandrite laser using an original composite cavity which includes an additional external dispersive cavity is confirmed. Conditions for narrow-band (less than 20 pm) radiation generation in this cavity with a possibility of smooth tuning the lasing wavelength in the spectral range 740–780 nm are experimentally studied. Narrow-band lasing in an alexandrite laser with a radiation energy of 30 mJ and a pulse duration of 35 ns is shown. The created compact narrow-band alexandrite laser can be an effective alternative to parametric oscillators (OPO) and Ti:Sapphire lasers in lidar systems operating in the spectral range 700–850 nm.

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.

This paper presents the results of mathematical modeling of the process of laser excitation of a phosphorus oxide (PO) molecule into the electronic states A2Σ+ and B2Σ+ with subsequent relaxation, taking account of the PO interaction with molecules of gas components of the real atmosphere. Dependences of intensity of the γ- and β-systems of phosphorus oxide fluorescence bands on the energy and time parameters of exciting laser radiation are obtained. The optimal pulse duration is shown to increase with increasing energy density of the exciting radiation.

Развитие лазерных технологий приводит к повышению требований, предъявляемых к разрабатываемым лазерам, генерирующим узкополосное излучение с различными длинами волн. Повышается значимость использования перестраиваемых по длинам волн диодных и вибронных лазеров, имеющих широкополосные контуры усиления. В работе показана возможность формирования в твердотельном лазере на александрите высококогерентного излучения при использовании оригинального составного резонатора, включающего в себя дополнительный внешний дисперсионный резонатор. Приведены результаты экспериментальных исследований по определению условий формирования в таком резонаторе узкополосного (менее 20 пм) излучения с возможностью плавной перестройки длины волны генерации в спектральном диапазоне 740–780 нм. Продемонстрировано получение в александритовом лазере узкополосной генерации с энергией излучения 30 мДж и длительностью импульса 35 нс. Созданный компактный узкополосный александритовый лазер может эффективно заменять параметрические генераторы и Ti:Sapphire-лазеры в лидарных системах, работающих в диапазоне 700–850 нм. The development of laser technologies leads to high requirements for lasers being developed which generate narrow-band radiation with different wavelengths. In view of this, the importance of wavelength-tunable diode and vibronic lasers with broadband amplification circuits increases. The possibility of generating highly coherent radiation in a solid-state alexandrite laser using an original composite resonator which includes an additional external dispersive resonator has been demonstrated. The results of experimental studies of conditions for the generation of narrow-band (less than 20 pm) radiation in such a resonator with the possibility of smooth tuning of the lasing wavelength in the spectral range 740–780 nm are presented. Narrow-band lasing in an alexandrite laser with a radiation energy of 30 mJ and a pulse duration of 35 ns was demonstrated. The created compact narrow-band alexandrite laser can be an effective alternative to parametric oscillators (OPO) and Ti:Sapphire lasers in lidar systems operating in the spectral range 700–850 nm.

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.

The results of experimental and theoretical studies of the operation of an electric-discharge KrCl laser (λ = 222 nm) at pump power densities of 10 MW/cm3 are presented. The radiation energy obtained experimentally was 55 mJ for a mixture with He as a buffer gas and 120 mJ for a mixture with Ne at a pump pulse duration of 30 ns. A numerical model of a KrCl laser using a He/Ne/Kr/HCl gas mixture with a uniform pump discharge is described. It is shown numerically that the dependence of the optimal (from the point of view of obtaining maximum radiation energy) pump power density on the partial pressures of the buffer gas and HCl is close to linear.

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.

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).

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

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.

We report the results of experimental and numerical investigations of a discharge KrF laser with specific pump power of 3.5 and 7 MW/cm3; generation is obtained with specific radiation pulse energy of about 6 and 9.5 J/L for an internal energy efficiency of about 4%. Time dependences of the formation of charged and excited particles in a dense excimer plasma with an electron concentration of ~1016 cm–3 are obtained. The conditions for effective operation of the laser are proposed, which will ensure a further increase in the specific radiation energy by more than two times with preserved high internal laser efficiency relative to the energy input into the discharge.