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Fourier Transform Spectroscopy (FTS)

Fourier Transform Spectroscopy (FTS). Yousaf Iqbal PEP Uni-Bremen. Outlines. Introduction to FT – IR Why Infrared spectroscopy FT – IR is preferred over dispersive IR spectropscopy Working Principle of FT – IR Michelson Interferometer Interferrogram & Fourier transformation

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Fourier Transform Spectroscopy (FTS)

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  1. Fourier Transform Spectroscopy (FTS) Yousaf Iqbal PEP Uni-Bremen

  2. Outlines • Introduction to FT – IR • Why Infrared spectroscopy • FT – IR is preferred over dispersive IR spectropscopy • Working Principle of FT – IR • Michelson Interferometer • Interferrogram & Fourier transformation • Advantages of FT – IR • Instrument in Bremen • How to get Transmission spectrum • Summary • Acknowledgement

  3. Introduction to FT – IR • FT – IR stands for Fourier Transform Infrared. Informations provided by FT – IR • Identify unknown material. • Determine the amount of component in a mixture. • Determine the quality of a sample. www.thermonicolt.com

  4. Why Infrared Spectropcopy • In infrared spectrum, apsorption peaks represent a fingerprint of a sample. • Absorption peaks --- frequencies of vibrations between bonds of atoms. • Different sample --- unique combinations of atoms. • No two compounds produces same spectrum. • Qualitative analysis of the sample. • Size of peaks ---- amount of material present.

  5. FTS is preferred over dispersive IR spectropscopy • Non-despersive technique • Provides presise measurement method without external calibration. • Greater optical throughput. • Mechanically simple (only one moving part)

  6. Working Principle of FT – IR • Infrared light emitted from the source. • Emitted light is directed into the interferrometer. • After interferrometer, light passes through the sample compartmet. • At the end focused on the detector. • The signal measured by the detector is called interferrogram. General FT-IR Spectrometer layout Bruker Optics http://www.brukeroptics.com/

  7. Bruker Optics http://www.brukeroptics.com/

  8. Michelson interferrometer Bruker Optics http://www.brukeroptics.com/

  9. high low high S D S S Intensity dOOOOOOPD Signal position Signal Measured d dOPD at detector (time average) Interference pattern Dr. Justus Notholt Institute for Environmetal Physics University of Bremen

  10. http://www.wooster.edu/chemistry/is/brubaker/ir/ir_works_modern.htmlhttp://www.wooster.edu/chemistry/is/brubaker/ir/ir_works_modern.html

  11. Interferogram & Fourier transformation • Interference ---- Resulting singnal is called Interferogram. • Make up the signal having information about every IR frequency which comes from source. • For identification, frequency spectrum is requried. • Means of decording frequency via Fourier transformation. Bruker Optics http://www.brukeroptics.com/

  12. Advantages of FT – IR • Light throughput advantage (Jaquinot advantage) • Multiplex principle (Fellget advantage) • Wavelength accuracy (Connes advantage) • Mechanical Simplicity

  13. Grating FTS Grating Circular aperture  more light Light throughput advantage (Jacquinot Advantage) Dr. Justus Notholt Institute for Environmetal Physics University of Bremen

  14. Multiplex principle (Fellget advantage) • All wavelengths at once. • More light (for single detectors)

  15. FTS Grating He-Ne laser 632.8 nm Wavelength accuracy (Connes Advantage) sin a ~ l Intensity dx 632.8 nm

  16. Mechanical Simplicity • Only moving mirror in FTS • Little possibility of mechanical breakdown.

  17. Instrument in Bremen

  18. Observations onboard of polarstern Cruise Dr. Justus Notholt Institute for Environmetal Physics University of Bremen

  19. How to obtained Transmission spectram Bruker Optics http://www.brukeroptics.com/

  20. The final Tramission Spectrum Bruker Optics http://www.brukeroptics.com/

  21. Comparison between the emission line (TB,a) and absorption lines of gases from the database TB,a H2O CO2 Intensity CH4 Wavenumber cm-1 Yousaf Iqbal and Irshad Ahmad University of Bremen

  22. Summary • FTS was developed in order to overcome the limitations of despersive instruments. • Fts measures all frequencies of IR simultaneously. • Interferometer ---- interferogram------ Fourier transformation of interferogram ---- spectrum

  23. Acknowledgements • http://www.thermonicolt.com • Bruker Optics http://www.brukeroptics.com/ • Dr. Justus Notholt Institute for Environmetal Physics University of Bremen • http://www.wooster.edu/chemistry/is/brubaker/ir/ir_works_modern.html

  24. Thanking you • Any questions Please

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