1 09:05-09:55 am, wednesday, september 22, 2010 chem 8152: analytical spectroscopy smith 1111,...
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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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