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09:05-09:55 am, Wednesday, September 22, 2010

CHEM 8152: Analytical SpectroscopySmith 1111, University of Minnesota

Resonant cavities

Gain

Threshold population to achieve oscillation

Achieving resonance

Longitudinal modes

Coherence

Pulse length / resolution tradeoff

Laser pulse characteristics

2T. Ditmire, American Scientist, 98, 394-401 (2010)

50th Anniversary: Discovery of the Laser

3T. Ditmire, American Scientist, 98, 394-401 (2010)

Pumping (Absorption) & Stimulated Emission

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Stimulated Emission

2 1E -E /kT2 1N -N = e

5T. Ditmire, American Scientist, 98, 394-401 (2010)

CW vs. Mode-Locked Laser

Mode-Locked = fixed phase

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Mode-Locked Laser Characteristics

8 1

8 1

L = = resonant cavity condition/ 2

c/2L

c = 3 x 10 m s

L 1.5 m

10 s = 100 MHz

q

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• Uncertainty principle lower limit: ΔtΔν ~ 5000 fs cm-1

Pulse Length / Resolution Limits

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1

1

1000 fs 5 cm

100 fs = 50 cm

10 fs = 500 cm

8T. Ditmire, American Scientist, 98, 394-401 (2010)

Chirped Pulse Amplification

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Femtosecond Stimulated Raman Spectroscopy

Kukura, P.; McCamant, D. W.; Mathies, R. A., Annu. Rev. Phys. Chem., 2007, 58, 461-488.

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• Uncertainty principle lower limit: ΔtΔν ~ 5000 fs cm-1

• FSRS is capable of attaining ΔtΔν ~ 500 fs cm-1

• Possible because observed variables are decoupled

Kukura, P., D.W. McCamant, and R.A. Mathies, Femtosecond stimulated Raman spectroscopy. Annu. Rev. Phys. Chem., 2007. 58: p. 461-488.

Pulse Length / Resolution Limits

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Kukura, P., D.W. McCamant, and R.A. Mathies, Femtosecond stimulated Raman spectroscopy. Annu. Rev. Phys. Chem., 2007. 58: p. 461-488.

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Kukura, P., D.W. McCamant, and R.A. Mathies, Femtosecond stimulated Raman spectroscopy. Annu. Rev. Phys. Chem., 2007. 58: p. 461-488.

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Pulse Characteristics

0 i ti tE t I t e e

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s

Pump Laser

Probe Laser Is(0)

Gain MediumIp Is> Is(0)

<Ip

Femtosecond Stimulated Raman Spectroscopy

Kukura, P.; McCamant, D. W.; Mathies, R. A., Annu. Rev. Phys. Chem., 2007, 58, 461-488.

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FSRS Apparatus

35 fs, 800 nm, 10 J, 250 KHz

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Accessible Spectral Window, Time Resolution, and Molecular Modes Probed by Vibrational Spectroscopic Techniques Used

To Monitor Structural Dynamics

Kukura, P., D.W. McCamant, and R.A. Mathies, Femtosecond stimulated Raman spectroscopy. Annu. Rev. Phys. Chem., 2007. 58: p. 461-488.

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