Laser-induced fluorescence of PO-photofragments of dimethyl methylphosphonate

The paper presents the results of calculating the absorption spectrum of a phosphorus monoxide (PO) molecule corresponding to the A(2)Sigma(+)(v' = 0) - X-2 Pi (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 (P-22 + Q(12)) and P-12 branches of the A(2)Sigma(+)(v' = 0) - X-2 Pi(3/2) (v '' = 0) band provides spectral separation of the (0, 1) gamma-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) gamma-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. (C) 2022 Optica Publishing Grou

Estimation of the limiting sensitivity of laser fragmentation/laser-induced fluorescence technique for detection of nitrocompound vapors in atmosphere

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

Efficiency of laser excitation of PO photofragments of organophosphates

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

Simulation of the transfer function of a Fabry-Perot interferometer for incoherent doppler wind lidar

The paper substantiates the choice of the slope of the spectral characteristic of the Fabry-Perot interferometer (FPI) for an incoherent Doppler lidar. The results of numerical simulation of the relative sensitivity of the FPI transmission with a change in the wind speed in the atmosphere by 1 m/s are presented for various FPI bases

Laser-induced fluorescence of PO photofragments of organophosphates

The spectrum of phosphorus monoxide (PO) fluorescence is calculated. It is shown that the use of excitation radiation at wavelengths near the bandheads of the (P22 + Q12) and P12 branches of the A2Σ+ (v′ = 0) − X2Π3/2 (v′′ = 0) band provides a spectral separation of the γ (0, 1) PO fluorescence band and the vibrational–rotational Raman spectrum of oxygen. The spectra of the γ (0, 1) fluorescence band of PO fragments of dimethylmethylphosphonate and the vibrational-rotational band of spontaneous Raman scattering on atmospheric oxygen molecules are experimentally obtained under exposure to KrF-laser radiation at a wavelength of 247.78 nm. It is shown that the shape and position of the fluorescence spectra calculated agree well with the experimental data

Analysis of the correctness of retrieving the vertical atmospheric temperature distribution from lidar signals of molecular scattering at the main lidar of the Siberian Lidar Station

The methodological issues of lidar measurements of the vertical distribution of atmospheric temperature up to altitudes of 90 km are considered. The method is based on lidar measurements of the vertical profile of atmospheric molecular density using the Rayleigh scattering effect. The results obtained in the upgraded channel of the Rayleigh scattering of the 2.2-m diameter lidar based on the main mirror of the Siberian Lidar Station (SLS) are discussed. One of problems in carrying out measurements with the use of large-diameter telescopes is the giant dynamic range of lidar responses. The work with this range requires special attention both to the methodology and to the experimental technique. For solving this problem, an improved technique for the retrieval of temperature from molecular backscattering lidar signals is proposed. Numerical experiments have shown that the accuracy of the temperature profile retrieval depends on the choice of the position of the calibration point and the error in setting the temperature in it. The technique of the temperature profile retrieval, when the calibration point is chosen at the top of a sounding path, is sufficiently stable even under conditions of a giant dynamic range of lidar responses at the SLS. The comparison of the results of temperature retrieval from the real lidar responses with the satellite measurement data revealed significant discrepancies associated with the distorting instrumental and atmospheric effects on the lidar signal shape. A correction procedure based on the lidar calibration can significantly reduce measurement errors

Photon counting system with automated detection and selection of photodetector discrimination thresholds

The paper considers a block diagram of a photodetection system based on a new version of the four-channel photon counter "PHCOUNT-4" used for precision lidar measurements of atmospheric temperature. The results of using the new capabilities of the analog part of the photon counting system, which makes it possible to automatically record the amplitude distribution of single-electron pulses of each of the photodetectors installed in the channels and determine the optimal discrimination threshold, are described. It is shown that setting the optimal discrimination thresholds makes it possible to achieve a small spread in the end-to-end quantum efficiency of each of the channel

Possibility of recording the unbiased scatter lidar signals in the altitude range of 30÷100 km on the main SLS lidar

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 0ч30 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