Yu. N. Ponomarev

Design and characteristics of a differential Helmholtz resonant photoacoustic cell for infrared gas detection

The Helmholtz resonant photoacoustic (PA) cell is a very convenient design of PA system for air pollution monitoring based on infrared molecular absorption. A simple differential Helmholtz resonator designed for flow measurements is presented in this work. The investigation of the PA systems characteristics based on this design includes experimental study of the responsitivity both of the separate photoacoustic cell and the whole photoacoustic system applied to trace gases detection. The experimental observations are compared to the theoretical predictions. A simple arrangement to enhance the photoacoustic signal of the whole system by a factor of 2 is presented.

IR spectroscopy of water vapor confined in nanoporous silica aerogel.

The absorption spectrum of the water vapor, confined in the nanoporous silica aerogel, was measured within 5000-5600 cm(-1) with the IFS 125 HR Fourier spectrometer. It has been shown, that tight confinement of the molecules by the nanoporous size leads to the strong lines broadening and shift. For water vapor lines, the HWHM of confined molecules are on the average 23 times larger than those for free molecules. The shift values are in the range from -0.03 cm(-1) to 0.09 cm(-1). Some spectral lines have negative shift. The data on the half-widths and center shifts for some strongest H(2)O lines have been presented.

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.

Water vapor continuum absorption in near-IR atmospheric windows

The near-infrared water vapor absorption is measured in the 2000–8000 cm−1 spectral region. Spectra were recorded using an IFS 125 HR Fourier spectrometer at a temperature of 287 K and a spectral resolution of 0.03 cm−1. The water vapor continuum absorption spectrum is retrieved using the known absorption in the 2500 cm−1 region as a reference point. It is shown that the continuum absorptions in four windows differ by no more than 20% under investigation conditions. This contradicts the MT_CKD continuum model, which predicts a much stronger variability of the continuum in these windows.

A Fourier-spectrometer with a 30-m base-length multipass cell for the study of weak absorption spectra of atmospheric gases

The design and specifications of the experimental set-up, consisting of an IFS-125 HR Fourier spectrometer and a 30-m base length multipass cell with the White optical system, are described. An optical path length of more than 600 m is attained. Results of measurement of atmospheric air spectra with a spectral resolution of 2 × 10−2 cm−1 and a sensitivity of less than 10−8 cm−1 are presented. It is shown that the complex reliably detects very weak absorption spectra of atmospheric molecules, including their isotopic modifications.

Spectroscopic nanoporometry of aerogel

The sizes of aerogel nanopores from the measured broadening of rotational-vibrational CO lines caused by collisions with nanopore walls have been determined. It has been shown that the sizes of nanopores with a diameter of 15–25 nm can be reliably assessed from the half-widths of spectral lines measured on a high-resolution Fourier spectrometer and agree well with the experimental data found from the low-temperature adsorption of nitrogen.

Modeling of helicopter-borne tunable TEA CO2 DIAL system employment for detection of methane and ammonia leakages

Abstract The characteristics of a helicopter-borne lidar based on tunable TEA CO2 laser and its third harmonic designed for remote detection of methane and ammonia leakages from pipelines are analyzed numerically. The spectral range near 3 μm was shown to be most promising for remote sensing of methane emissions. Parameters of radiation of the tunable pulse-periodic mini-TEA CO2 laser and generators of harmonics to be utilized in the helicopter-borne differential absorption lidar are estimated. Emissions of different gas intensities are analyzed for possible detectability at a distance of up to 1 km. The use of the third harmonic of the TEA CO2 laser allows methane emissions from a pipeline to be detected and measured with mean measurement error from 10% to 15% for methane concentrations varying from the background level to the explosion-hazardous one. The optimal pair and possibilities of the ammonia remote sensing on the base of the first harmonic of TEA CO2 laser were determined as well.

Observation of a forbidden vibrational absorption band of H2 in nanoporous aerogel

Room-temperature absorption spectra of H2 in nanoporous aerogel with a pore diameter of ∼20 nm have been studied on a Fourier spectrometer in the spectral range of 4000–4800 cm−1. Absorption at the forbidden transitions of the 0–1 vibrational band has been observed. The recorded spectra of H2 in aerogel have been compared with the spectra of free high-pressure H2.

Variation of H 2 O, CO 2 , and CO 2 Isotope Composition in Tree Rings of Siberian Stone Pine

The experimental measurements of H2O, CO2, and the carbon isotope content of CO2, vacuum-desorbed from tree rings of the Siberian stone pine disc, have been obtained. It is shown that: 1) certain cyclicity exists in annual trends of H2O and CO2; 2) the amplitude of CO2 cycles has markedly risen after 1960; 3) the annual trend of the CO2 concentration in the rings correlates with an increase in atmospheric CO2 concentration; 4) the carbon isotope content varies with the variation of CO2 concentration in a sample.

Parametrization of transmittance for application in atmospheric optics

Abstract Different ways of improving the line-by-line method are described. Peculiarities of the application of the k-distribution method to parametrization of transmittance of overlapping bands for atmospheric gases are discussed. An expansion of the transmittance in exponential series with parameters determined on the basis of absorption coefficients is proposed.