Connecticut College, New London, Connecticut usa general Physics Institute, Russian Academy of Sciences, Moscow, Russia
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Lecture 12.MOLECULAR LINE SHAPE ANALYSIS OF TDL SPECTRA BY MULTISPECTRUM FITS ACCOUNTING FOR FINE COLLISIONAL EFFECTS 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 The tunable diode laser spectrometer, located at LPMA in Paris, which is actively controlled by a Michelson interferometer, is characterized by a signal-to-noise ratio of about 2000 and a frequency stability better than 410-5 cm-1(1). It allows not only to record precisely spectral lines in order to determine their line shape parameters (intensities, broadening, shift…) but also to quantitatively record very weak absorption lines in the frame of atmospheric applications (concentration measurements). Achieving such high performances implies to model line shapes as well as instrumental effects to a comparable precision. Recent theoretical developments (see e.g.: (2-4)) produced a rather extended variety of semi empirical line shapes models describing the collision (pressure) broadening, the molecular confinement (Dicke narrowing), the line mixing, and the speed dependence of the lines parameters not only in limit cases but also in intermediate regimes. Most of these effects produce usually rather fine deviations from the Voigt profile and are acting prominently in limited pressure ranges. To help to disentangle partly the contributions of each of these effects and to improve the precision on the determination of the line parameters, we have developed a multi spectrum fitting software that can handle simultaneously a large set of spectra recorded under different pressure conditions. Most of the recent models have been included in the code. We will illustrate the technique on selected molecular mixtures samples recorded from room temperature down to 20K (using a collisional cooling cell(5)) with the LPMA spectrometer either in the mid infrared, using lead salt diodes, or in the near infrared, using distributed feed-back diodes. The ability of the models at describing the experimental spectra, the relevance of the line shape parameters and their relation to the knowledge of the instrumental contribution will be discussed. 1. A. Valentin, Spectrochim. Acta Part A 52, 823-833 (1996) 2. R. Ciurylo, Phys. Rev. A 58, 1029-1039 (1998) 3. A. S. Pine, J. Quant. Spectrosc. Radiat. Transfer 62, 397-423 (1999) 4. R. Ciurylo and Pine A. S., J. Quant. Spectrosc. Radiat. Transfer 67, 375-393 (2000) 5. J. K. Messer and F. C. De Lucia, Phys. Rev. Lett. 53, 2555-2558 (1984) Lecture 13.MID-INFRARED COHERENT SOURCES BASED ON MICROSTRUCTURED NONLINEAR MATERIALS Martin Fejer E. L. Ginzton Laboratory/Stanford University/Stanford, CA 94305/fejer@stanford.edu Rapid progress in the technology of semiconductor lasers over the past several years has enabled new generations of mid-IR sensors. Most work in this spectral range has focused on conventional and quantum cascade lasers emitting in the mid-IR, designed specifically for these applications. Despite the impressive results obtained with these mid-IR lasers, alternative sources based on nonlinear frequency conversion, that take advantage of the near-IR lasers whose development has been stimulated by the enormous recent investment in optical communications, offer some interesting opportunities. In this talk, progress on mid-IR sources based on microstructured nonlinear materials will be described. Several types of nonlinear sources, including difference frequency generation (DFG), optical parametric amplifiers/generators, and optical parametric oscillators, can be applied to the generation of mid-IR generation. In all these sources, a near-IR pump (or two near-IR pumps) is converted to the mid-IR through a nonlinear interaction, in which the frequencies of the three interacting waves are related by  , where p, s, i represent pump, signal, and idler respectively. A key aspect of all such interactions is the requirement of phasematching, i.e. compensating for the normal material dispersion which normally violates the momentum conservation condition,  , where the k are the propagation constants of the interacting waves. In microstructured materials, with a nonlinear susceptibility that can be modulated in a periodic fashion, a “quasi-phasematching” (QPM) condition,  , where  is the k-vector of the pattern imposed on the nonlinear coefficient, with a period  . Interactions in such quasi-phasematched offer notable advantages over those in conventional birefringently phasematched media, most notably the ability to “design” a material for essentially any operating wavelength through patterning of an appropriate QPM grating, and the use of the largest, often diagonal, nonlinear coefficient in the material. Two types of materials in which the sign of the nonlinear coefficient can be controlled have been exploited for QPM generation of mid-IR radiation, ferroelectric oxides in which the periodic reversal of domains of spontaneous electric polarization is obtained through application of electric fields on lithographically-patterned electrodes, and orientation-patterned GaAs grown on “template” substrates. Another important tool for increasing the efficiency of these interactions are dielectric waveguides, formed for example by indiffusion of a dopant into a QPM substrate, in which tight optical confinement can be obtained over long interaction lengths.
Examples of the types of sources possible in these media include milliwatt-level sources in the 2 – 4 m spectral range by DFG in periodically-poled lithium niobate (PPLN) waveguides with spectral linewidths controlled by the near-IR pump lasers, and sources broadly tunable in the 8 – 10 m range in orientation-patterned GaAs. Examples of such sources and their application in spectroscopic measurements will be presented. Directory: 2003 2003 -> Tr-41. 4-03-05-024 Telecommunications 2003 -> Review of some tsunamis in canada 2003 -> The skill of multi-model seasonal forecasts of the wintertime North Atlantic Oscillation 2003 -> 2930 Kerry Forest Parkway 2003 -> Canadian Interuniversity Sport (cis) Athletes of the Week 2003 -> Senior Airman Jason Plite Hometown 2003 -> Technical announcements: My apologies for the comparison pages; they were 2003 -> Pool Play Round 1 9: 20: 00 am 2003 -> 2004 Division II men's Golf Championships Final Round Results deland, fla 2003 -> Go Figure Edited by Kostya Kennedy and Mark Bechtel 645 Passing yards, an ncaa division II record, by University of Indianapolis quarterback Matt Kohn, in a 59-52 victory over Michigan Tech Download 1.65 Mb. Share with your friends:
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