B. A. Tikhomirov

Influence of the shift H2O absorption lines with air pressure on the accuracy of the atmospheric humidity profiles measured by the differential-absorption method

The variation with pressure of the centers of absorption lines of atmospheric H(2)O has been investigated experimentally using ruby and neodymium lasers. A numerical analysis of possible errors resulting from pressure shifts in the solutions of the inverse problem in remote laser sensing of vertical humidity profiles has been made.

Nonlinear absorption of intense femtosecond laser radiation in air

A new mechanism of nonlinear absorption of intense femtosecond laser radiation in air in the intensity range I = 10(11)-10(12) W/cm(2) when the ionization is not important yet is experimentally observed and investigated. This absorption is much greater than for nanosecond pulses. A model of the nonlinear absorption based on the rotational excitation of molecules by linearly polarized ultrashort pulses through the interaction of an induced dipole moment with an electric field is developed. The observed nonlinear absorption of intense femtosecond laser radiation can play an important role in the process of propagation of such radiation in the atmosphere.

Photoacoustic measurements of the vibrational relaxation of the selectively excited ozone (ν3) molecule in pure ozone and its binary mixtures with O2, N2, and noble gases

The vibrational-translational relaxation time of the ν3 state of ozone was deduced from the phase shift of the photoacoustic detector signal relative to the amplitude-modulated radiation of the CO2 laser used for excitation of O3. A special photoacoustic cell with a third electrode is used to eliminate an instrumentation phase shift caused by inertia of the microphone membrane. A three-level kinetic model of O3 is presented and used to fit the experimental and calculated phase shifts to determine the vibrational relaxation rate coefficients for pure O3 and binary mixtures of O3 with O2, N2, and noble gases He, Ne, Ar, Kr, and Xe. These results are presented and compared with experimental data obtained for O3, O3–O2, and O3–N2 by fluorescence and double resonance techniques. Experimental data for ν3 state relaxation in binary mixtures with all noble atoms have been obtained for the first time. These new results are compared with the simplest model of interaction. Thus we obtain a very good agreement for th...

The problem of water vapor absorption in the UV spectral range

The review of literature data and results of a series of experiments, made by the authors, shows that the problem of UV absorption by atmospheric water vapor has not yet been solved satisfactorily. The attempts to propose a reliable model of atmospheric H2O contributions to the attenuation of UV radiation propagating through the atmosphere or for analysis of data obtained with instruments for atmospheric composition monitoring have not been successful. Additional measurements of the spectral dependence of the absorption cross-section within the 200–400 nm range are required.

Nonlinear absorption of ultraviolet femtosecond laser pulses in argon

The optogalvanic and optoacoustic methods are used to determine the mechanisms of the nonlinear absorption of intense ultraviolet femtosecond laser pulses in gaseous argon. An increase in the nonlinearity of the absorption process from 3 to 4 with an increase in the laser radiation intensity in the range 0.03–12 TW/cm2 is revealed. The possible physical mechanisms of this phenomenon are discussed.

Preliminary results on photoacoustic study of the relaxation of vibrationally excited ozone (ν3)

Abstract The vibrational translational relaxation time of ν 3 state of ozone was measured from the phase shift of the photoacoustic signal relative to the amplitude-modulated radiation of the CO 2 laser used for excitation of O 3 . A special photoacoustic cell with a third electrode is used to eliminate an instrumentation phase shift caused by inertia of the microphone membrane. A three-level kinetic model of O 3 is used to fit the experimental and calculated data of the phase shift and to determine the vibrational relaxation rate coefficients for pure ozone.

Sorption of Atmospheric Gases (N2, O2, Ar, CO2, and H2O) by Silica Aerogel

Adsorption and desorption of atmospheric gases (N2, O2, Ar, CO2, and H2O) in silica aerogel is studied. Static parameters of adsorption and kinetic parameters of adsorption and desorption are determined based on the pressure vs time dependence P(t) in the buffer vacuum chamber of an experimental setup during adsorption and desorption of gases in a SiO2 aerogel sample V = 42.8 cm3 in volume and ρ = 0.34 g/cm3 in density. The ratios of adsorbate molecular density to aerogel molecular density at room temperature T = 293 K and equilibrium pressure Pe ≈ 1 bar are found: γ(N2) = (9 ± 3)% (nine N2 molecules adsorbed by pore surface to 100 N2 molecules in the gas at equilibrium), γ(O2) = (7 ± 3)%, and γ(CO2) = (222 ± 8)%; for water vapor, γ(H2O) = (5.9 ± 0.3) × 104% at Pe = 5.7 mbar. It is ascertained that Ar atoms are not adsorbed by the aerogel. It is suggested to use argon as a “zero” gas in spectroscopy of molecules adsorbed by SiO2 aerogel to determine the amount of adsorbate in a sample. A sum of two exponential functions of kinetic parameters τ1 and τ2 is used to fit the P(t) dependence, where τ1 and τ2 values are estimated during the adsorption and desorption of each gas under study.

Photoacoustic measurements of UV laser Pulse (266 nm) absorption in mixtures of water vapor with nitrogen

Results of photoacoustic measurements of absorption of 266 nm-laser pulses (the fourth harmonics of a YAG laser) by mixtures of water vapor and nitrogen, depending on the radiation intensity (0.5–10 MW cm−2) and H2O partial pressure (0–10 mbar), are presented. It is shown that the linear absorption (in the given range of intensities) increases with H2O partial pressure in a range 0–5 mbar and remains almost stable in a range 5–10 mbar exceeding the absorption in the pure nitrogen only by two orders of magnitude.

Retrieval of the pressure signal form from a microphone pulse signal

A technique for computer retrieval of the pressure signal form from a pulse microphone signal is proposed. It is shown that the time of collisional relaxation of molecules from the excited state to the ground state can be measured on the basis of this technique with the use of a time-resolved photoacoustic spectrometer.

Investigation of signal shaping in opticoacoustic spectrometers with pulse excitation

The authors investigate the dependence of the shape of the time of the signal in opticoacoustic spectrometers with pulse excitation on the characteristics of the medium, the gas cell and microphone parameters, and the pulse laser generation mode, by means of a numerical and full-scale experiment. It is noted that an opticoacoustic method is used extensively for the analysis of gas mixtures, the measurement of weak optical radiation fluxes, the investigation of linear and nonlinear gas and vapor absorption, and the determination of the lifetime of excited atoms and molecular states.