A. Delahaigue

REIMS HIGH RESOLUTION FOURIER TRANSFORM SPECTROMETER. DATA REDUCTION FOR OZONE

Abstract The specificities and the performances of the Fourier transform spectrometer (FTS) located in Reims is described. Particular attention is focused on the automatic servo control and monitoring of this apparatus. Ozone spectra are used to illustrate the performance of the machine in the 5 μm range, including reduction of data with fits on line shapes, and excerpts of results concerning line positions, intensities, widths and shifts are given.

Spectre infrarouge à l'état solide des molécules isotopiques de SO2

Abstract We have observed the infrared absorption spectrum of the isotopic molecules of SO 2 with the natural abundance for sulfur-32 and -34 and oxygen-16 and with oxygen-18 at 97 per cent containing 0,4 per cent oxygen-17. We show that the preceding augments of bands [5], [6] are erroneous. The bands previously augmented to the interaction of the internal vibrations and the lattice vibrations are due to isotopics bands. On the other hand the form of band when the molecule is diluted in isotopic molecules and when it is surrounded by identical molecules shows that there is in intermolecular coupling. The great number of bands observed enables us to calculate the force constants in the solid state using the most general quadratic force field. We compare these force constants in solid state with those obtained in the gaseous state [10] and in the solid state in a Krypton matrix [7].

Atmospheric laser heterodyne detection

Abstract We describe in this paper what has been done for ten years at Reims in the area of atmospheric heterodyne laser spectrometry. The recent technical progress allows now to use this technique in two different ways. The first is devoted to the radiometry with low spectral resolution [0.1 cm −1 ] of “cold” gases (300 K) in the troposphere. The second is devoted to the transmission spectrometry of the atmosphere (high resolution 0.002 cm −1 ) with the sun as a blackbody source. In the particular case of ozone, the gas absorption lines are in the neighborhood of the CO 2 laser lines. The earlier ozone concentration measurements were precision limited because of the atmospheric CO 2 absorption and the total integration time (>30 min) of the recorded spectrum. An alternative improved method is presented where the atmospheric CO 2 absorption is eliminated with the use of a 18 O 12 O 18 O laser. An acousto-optic spectrometer (AOS) gives the multiplex advantage and reduces the total duration of a spectrum to only one minute.

Heterodyne spectrometer for the 10 micron region

We first consider the interest of infrared heterodyne spectroscopy to study the vertical distribution of atmospheric constituents such O3. Then an heterodyne spectrometer is described. It operates in the 10 micron region with a CO2 laser and gives a resolution of 5 MHz. A laboratory spectrum of C2H4 is presented as a preliminary result.

Frequency and amplitude stabilization device for a cw CO2 laser

Abstract The active stabilization of a cw CO2 laser is described. The servo control system uses frequency stabilization at the maximum of the power profile. Description of the high voltage current regulated supply is given together with details and diagrams of the electronics. The results obtained by this servo-control system are presented.

An instrument for atmospheric detection of NH3 by laser heterodyne radiometry

Abstract A laser heterodyne radiometer has been used to detect and to identify a pollutant in the atmosphere. In this paper we describe the technique based on the gas thermal emission measurement at 10 urn wavelength. A quantitative study of the NH3 detection is detailed.

Infrared laser heterodyne ozone spectrum

An infrared laser heterodyne spectrometer (IRLHS) has been developped for both laboratory and atmospheric studies. A long path and temperature adjustable cell has been designed for laboratory spectra. An ozone spectrum with 5MHz (0.00016 cm−1) resolution is presented.

Linewidth narrowing of 10 μm diode lasers by external feedback

Abstract The spectral emission of a mid-infrared diode laser at 10 μm is investigated by two different techniques. The fringes of a high finesse confocal etalon and the beats with a stabilized carbon dioxide laser are recorded. The conjugate effects of electronic frequency stabilization by using low-pressure gas molecule absorption and the controlled optical feedback in an external cavity are shown. The linewidth is reduced from 65 to 20 MHz.

Heterodyne spectra analysis

A complete explanation of heterodyne spectra is given here. The study of the folding effect has been carried out and the properties of heterodyne spectra are detailed. A fitting method using synthetic spectra is developed. Ozone heterodyne spectrum is taken as an example.

Thermal emission detection by laser heterodyne radiometry

Abstract A selective black body is considered as a self-emitting source and can be characterized by its remote thermal emission. This emission is detected at 10 μm wavelength by a laser heterodyne radiometer. Temperature, spectral, and spatial resolution conditions are given. The experimental set-up is fully described and signal-to-noise ratio measurements are presented.