Connecticut College, New London, Connecticut usa general Physics Institute, Russian Academy of Sciences, Moscow, Russia
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E13.A labVIEW based automated near infrared tunable diode laser high resolution spectrometer for -OH second overtone detection S.Shaji*, Shibu M Eapen, T.M.A.Rasheed** and K.P.R.Nair Laser and Spectroscopy Lab, Department of Physics, Cochin University of Science and Technology, Cochin - 682 022, INDIA. *e-mail: shajis@cusat.ac.in Phone : +91484 2577404 **Department of Physics, College of Medicine (P.O Box-2114), King Faisal University, Dammam 31451, K.S.A., e-mail: tmarasheed@yahoo.co.in A tunable diode laser absorption spectrometer for high resolution –OH second overtone spectra is described in this paper. A Tunable diode laser operating between 936 nm – 976 nm with 0.01 nm tunability is used as the source, a multipass cell with an optimum pathlength of 36 m which can be used at low pressure and a high sensitivity solid state photodetector. Tunable diode lasers with narrow radiation line allows realization of ultimate spectral resolution of linear spectroscopy. In laser absorption spectroscopy, the absorption signal strength is proportional to the product of oscillator strength of the absorption transition and the number of molecules in the path of the laser beam. The use of multipass optical systems as sample holders provides longer path length and facilitates operation at low pressure and thus avoids broadening of spectral lines with better absorption. The control of the laser and data acquisition is done by interfacing the setup to a PC using Labview 6.0 software and the necessary hardware. The setup is calibrated using the absorption lines of water vapor from HITRAN 96 database [1, 2] and OH second overtone in methanol [3]. The spectrometer using a tunable diode laser with tunability range 936-976 nm is advantageous to study the spectrum of the OH group absorption frequencies in all OH containing molecules in the transition region DV = 3. By using a detector with log output, the chopper and lock-in-amplifier can be avoided. References [1] www.hitran.com [2] L.S.Rothman, C.P.Rinsland, A.Goldman, S.T.Massie, D.P.Edwards, J.M.Flaud, A.Perrin, C.Camy-Peyret, V.Dana, J.Y.Mandin, J.Schroeder, A.McCann, R.R.Gamache, R.B.Watson, K.Yoshino, K.V.Chance, K.W.Jucks, L.R.Brown, V.Nemtichinov and P.Varanasi; Journal of Quantitative Spectroscopy and Radiative Transfer, 60 (1998) 665 [3] Shibu M. Eappen, S.Shaji, T.M.A Rasheed and K.P.R Nair (Accepted for publication in Journal of Quantitative Spectroscopy and Radiative Transfer).
E14.DEVELOPMENT oF A STABILIZED LOW TEMPERATURE INFRARED ABSORPTION CELL FOR USE IN STANDARD LOW TEMPERATURE AND COLLISIONAL COOLING EXPERIMENTS. Alain Valentin, Annie Henry, Christophe Claveau. Laboratoire de Physique Moléculaire et Applications (C. N. R. S.), Université Pierre et Marie Curie, 4 Place Jussieu, Tour 13, Case 76, F-75252 Paris Cedex 05, Daniel Hurtmans Service de Chimie Quantique et de Photophysique (Atomes, Molécules et Atmosphères), formerly « Laboratoire de Chimie Physique Moléculaire », Université Libre de Bruxelles, CP 160/09, 50 Av. F.D. Roosevelt, B-1050 Bruxelles, Belgium Arlan W. Mantz Department of Physics Astronomy and Geophysics, Connecticut College, 270 Mohegan Avenue, New London, Connecticut 06320 USA The feasibility of adapting the collisional cooling technique, originally described by De Lucia and co workers, see for example (1), using microwave transitions, to the study of infrared transitions utilizing tunable diode lasers was first demonstrated several years ago by Mantz and co workers (2) In an effort to improve the accuracy in the determination of spectral line parameters at temperatures as low as 7 K, we have constructed and tested a low temperature cell using the open cycle liquid helium technique. The cell has an absorption path of 16.8 cm. The temperature range over which this cell is actively temperature controlled is 200 K to 7 K. This is illustrated by spectra of carbon monoxide perturbed by argon or helium using the collisionnal cooling technique for the lowest temperatures. The temperature stability of the cell is better than 0.1 K. With this approach the temperature dependence of spectral line parameters can be accurately determined. In these experiments we use an interferometer controlled multi beam tunable diode laser spectrometer developed at LPMA and recently modified to permit the simultaneous recording of analytical and reference spectra. The simultaneous recording of a reference spectrum with the analytical spectrum overcomes systematic effects coming from the instrument itself and gives the possibility to accurately measure the pressure shift and its temperature dependence. The line and instrumental parameters are determined by a multi-spectra fitting software which incorporates most of the recent line shape models. Results of simultaneous analyses are discussed by D. Hurtmans in an invited paper in which this multi spectral technique is thoroughly described. In this poster we will provide a complete description of the cell and some line parameters determined for sample temperatures down to 7 K. 1. J. K. Messer and F. C. De Lucia, Phys. Rev. Lett. 53, 2555-2558 (1984) 2. D. R. Willey, K. A. Ross, V. Dunjko and A. W. Mantz, J. Mol. Spectrosc. 168, 301-312(1994). E15.Measurement of CH4 concentration in the stratosphere by means of an airborne near-infrared diode laser analyzer F. D'Amato SIT S.r.l., Via delle Case Dipinte 17, 56127 Pisa, Italy M. De Rosa, P. Mazzinghi, M. Pantani, P.W. Werle Istituto Nazionale di Ottica Applicata, Largo E. Fermi 6, 50125 Firenze, Italy We present the results of the measurements of CH4 concentration performed in a mid-latitude and in a polar campaign on board of "Geophysica" stratospheric aircraft. The analyzer is based on a room temperature, distributed feedback laser emitting at the wavelenght of 1.651 mm. The instrument is located in the bay in front of the rear left wheel of the aircraft. The air is sampled by a pipe pointing in the aircraft forward direction and is heated before entering the instrument. A computer driven valve closes the cell at altitudes lower than 5000 m. The instrument is divided into two parts, one containing the computer and the electronics, and the second containing the optics. The optical scheme is shown in the figure below. The laser beam is divided into two beams. One of them is sent across a reference cell, filled with pure methane, onto a reference germanium detector, used only for the active laser wavelength stabilization. The second beam interacts with air inside a Herriott-type multipass cell (SIT Mod. Aero-33) and is focalized onto a measurement detector (InGaAs-PIN). The detection technique is the two-tone frequency modulation spectroscopy. The temperature at the entrance and exit of the multipass cell is monitored by two sensors, as the reading is a function of temperature. The available space in the lower left corner will be used for an additional CO2 measurement channel. In this case the multipass cell will be smaller and the reference arm will be missing. The laser frequency is scanned across the methane absorbing multiplet 20 times per second. Each acquired waveform is processed separately, and the final value is averaged in an on-line rolling average. The time resolution is 1 second. Every second the computer stores the instrument reading and the main operating parameters (laser current and temperature, air temperature and pressure etc.). The calibration of the analyzer with respect to pressure will be discussed as pressure effects the number of absorbing molecules and on the shape of the absorption curve. With our detection scheme, this latter feature has a significant influence on the reading. 
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