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FTIR Spectrometer

FTIR Spectrometer. F ourier T ransform I nfra R ed Measures IR spectrum using interference of light beam with itself Depending on configuration, may measure properties of material sample (absorption, transmission, reflectance) or spectral characteristics of external source (atmosphere).

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FTIR Spectrometer

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  1. FTIR Spectrometer • Fourier Transform InfraRed • Measures IR spectrum using interference of light beam with itself • Depending on configuration, may measure properties of material sample (absorption, transmission, reflectance) or spectral characteristics of external source (atmosphere)

  2. Simplified Schematic • Incoming light split by beamsplitter and sent to two mirrors • Movable mirror(s) create a path difference or retardation between two beams • Upon recombination, each wavelength experiences constructive or destructive interference

  3. Monochromatic Light Interferogram:

  4. Continuum Source

  5. Finite Spectral Resolution • One cycle of beat frequency • Best resolution

  6. FT of truncated interferogram gives spectrum convolved with

  7. Apodization • Problem: Spectrum is corrupted by convolution • Solution: Instead of rect function, use triangular or other window (apodization)

  8. Some Apodization Functions

  9. Tradeoffs • Max retardation - Spectral resolution • Interferogram sampling - Spectral range • Noise - Scan averaging (SNR  N1/2) • Narrow peak - sidelobes

  10. CSU FTIR Spectrometer • Max spectral resolution: 1 cm-1 • Current spectral range: 500-2000 cm-1 • Calibration targets: ambient and LN2 blackbodies

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