[en] This letter was written in connection with the paper by A F Bunkin, A A Nurmatov, and S M Pershin (Usp. Fiz. Nauk 176 883 (2006) [Phys. Usp. 49 855 (2006)]) and the comments on this paper by A F Krupnov and M Yu Tretyakov (Usp. Fiz. Nauk 179 1363 (2009) [Phys. Usp. 52 (12) 1273 (2009)]). (letters to the editors)

[en] A review of the works that we have been carried in the last 5 years on the use of the method of absorption spectroscopy with diode lasers for the diagnosis of hot zone parameters is given. A spectrometer with two lasers operating in different spectral ranges with sufficiently strong absorption lines has been developed for the case of high pressures and gas temperature. The results of the search for optimal lines in different spectral ranges have been presented. The results of laboratory measurements and tests at the experimental power stand at TSAGI Named after Prof. N.E. Zhukovsky have been presented. Approaches to determining the maximum temperature for spatially inhomogeneous hot zones have been discussed. The method of difference spectra and method of fitting the experimental spectrum with the sum of one-temperature spectra have been proposed. The efficiency of the proposed processing algorithms for specific types of hot zones has been shown experimentally.

[en] A new two-temperature (2-T) algorithm for an estimation of the temperatures in a non-uniform hot zone by absorption spectrometry with tunable diode lasers (TDLAS) is demonstrated in experiments with the Wolfhard–Parker burner. A laminar premixed flame of the burner has a planar structure with zones of relatively constant temperature and zones with pronounced temperature gradients. The temperature was evaluated by fitting the experimental absorption spectra of a H₂O molecule by the linear combination of two single temperature spectra simulated using spectroscopic databases. The radiation of the two diode lasers generating in 7185 cm⁻¹ and 7444 cm⁻¹ spectral ranges crossed the flame in the direction along the slots at different heights above the burner. Temperature profiles of the flame obtained by fitting the line-of-sight TDLAS experimental spectra using a 2-T algorithm are compared with the local temperatures measured by coherent anti-Stokes Raman spectroscopy (CARS). The maximum and minimum temperatures estimated by the TDLAS and CARS coincide well if the line-of-sight optical path of the probing diode laser beam consists of a dominantly hot or dominantly cold layer. (letter)

[en] The layout of an absorption spectrometer with diode lasers for contactless measurement of the temperature and water-vapor concentration in gas flows with mixture pressures of up to 3 atm and temperatures of 300–2000 K has been designed. The technique is based on the rapid tuning of the radiation wavelength of two lasers, the registration of the absorption lines of water molecules that are located in the tuning range, and the fitting of the experimental absorption spectra by theoretical ones that have been simulated using spectroscopic databases. The original components of the spectrometer and different algorithms of the processing of experimental spectra are described. The performance of the spectrometer and processing methods were tested in the laboratory with a cuvette at a pressure of 1 atm and temperatures of 300–1500 K. The different processing algorithms give a reasonable coincidence of data on hot zone parameters that were obtained by the method of diode laser absorption spectrometry, and the temperature that was measured using standard sensors. The designed layout of the spectrometer passed the first tests on the T-131 experimental stand at the TsAGI (Central Aerohydrodynamics Institute).

[en] We report a procedure for temperature and water vapour concentration measurements in an unsteady-state combustion zone using diode laser absorption spectroscopy. The procedure involves measurements of the absorption spectrum of water molecules around 1.39 μm. It has been used to determine hydrogen combustion parameters in M = 2 gas flows in the test section of a supersonic wind tunnel. The relatively high intensities of the absorption lines used have enabled direct absorption measurements. We describe a differential technique for measurements of transient absorption spectra, the procedure we used for primary data processing and approaches for determining the gas temperature and H₂O concentration in the probed zone. The measured absorption spectra are fitted with spectra simulated using parameters from spectroscopic databases. The combustion-time-averaged (∼50 ms) gas temperature and water vapour partial pressure in the hot wake region are determined to be 1050 K and 21 Torr, respectively. The large signal-to-noise ratio in our measurements allowed us to assess the temporal behaviour of these parameters. The accuracy in our temperature measurements in the probed zone is ∼40 K. (laser applications and other topics in quantum electronics)

[en] An absorption spectrometer based on diode lasers is developed for measuring two-dimension maps of temperature and water vapour concentration distributions in the combustion zones of two mixing supersonic flows of fuel and oxidiser in the single run regime. The method of measuring parameters of hot combustion zones is based on detection of transient spectra of water vapour absorption. The design of the spectrometer considerably reduces the influence of water vapour absorption along the path of a sensing laser beam outside the burning chamber. The optical scheme is developed, capable of matching measurement results in different runs of mixture burning. A new algorithm is suggested for obtaining information about the mixture temperature by constructing the correlation functions of the experimental spectrum with those simulated from databases. A two-dimensional map of temperature distribution in a test chamber is obtained for the first time under the conditions of plasma-induced combusion of the ethylene – air mixture. (laser applications and other topics in quantum electronics)