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Femtosecond transient absorption

Femtosecond transient absorption. Pump and probe technique. Schematic layout of a typical femtosecond transient absorption apparatus. Main parts of the instrument. Excitation source Probe source Optical delay Detector. Pump. Probe. t=0. t<0. t>0. Pump and probe concept. t.

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Femtosecond transient absorption

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  1. Femtosecond transient absorption Pump and probe technique

  2. Schematic layout of a typical femtosecond transient absorption apparatus

  3. Main parts of the instrument • Excitation source • Probe source • Optical delay • Detector

  4. Pump Probe t=0 t<0 t>0 Pump and probe concept t

  5. Transient signal detection I0 I1

  6. Typical temporal characteristics • ~100 fs time resolution • Determined by the laser pulse duration • 1-6 ns time window • Determined by the optical delay length

  7. Excitation light sources • Direct Ti-Sapphire laser output • 800 nm • Harmonic generation • SHG 400 nm • THG 267 nm • Optical parametric amplification • 250-12000 nm

  8. Probe light sources • White light continuum generation • Advantage • Easy to use • All wavelengths are generated at once • Disadvantage • Somewhat limited spectral range 330-1000 nm

  9. Probe light sources • Optical parametric amplification • Advantage • Broad spectral range 250-12000 nm • Disadvantage • Requires more sophisticated equipment • Only narrow spectrum is generated at once, therefore – need to scan

  10. The method allows for: • Direct observation of a transient by monitoring a characteristic spectral signature • Observation of the electronic and vibrational energy redistribution • Probing broad spectral and temporal range in automated mode • Observation of stimulated emission

  11. The method does not allow for: • Direct observation of emission • Monitoring of structural changes

  12. Detectors (CCD)

  13. Detectors (CCD) • Advantages • Acquires the whole spectrum at once • Compact • Disadvantages • Reduced speed of data acquisition • More expensive

  14. Detectors (diodes)

  15. Detectors (diodes) • Advantages • Allows for faster data acquisition • Lower cost • Disadvantages • Limited to a single wavelength • Requires a monochromator • The setup with diodes is generally much more space consuming

  16. Typical data example

  17. Typical data example

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