Molecular Spectroscopy of Rotational, Vibrational, and Electronic oscillations

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• Molecular Spectroscopy of Rotational,
  Vibrational, and Electronic oscillations
• Abram Young
• University of Arizona, Dept. of Physics

J2,0 ? 1,0 Transition
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Generation of THz waves by Optical Rectification
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Reference pulse
Pulse through sample
Discrete Fourier Transform to recover spectrum
and phase
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THz signal through NH3 cell

• 11 cm cell with thin Mylar windows
• Evacuated to lt50 mTorr before each scan
• Adjustable pressure 0.1 100 Torr

0.119 pSec shift from vacuum sample approximates
index of refraction
NH3 Rotational transitions
Noise floor
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Low Order Rotational Lines

• J1,0 ?0,0 0.572 THz (0.597 THz)
• J2,0 ?1,0 1.215THz (1.193 THz)
• J3,0 ?2,0 1.765THz (1.790 THz)

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Future Measurements

• Sub-Doppler Lamb dip spectroscopy

Greatly reduced from atomic spectra due to
greater reduced mass and lower oscillation
frequency
For room temperature Ammonia, 1.8 MHz for J1lt-0
(3.6 MHz, 5 MHz for J2lt-1 and J3lt-2)
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5 Bands from 140GHz-900GHz
Signal conditioning
DC supplies

• Microlambda 10-20 GHz multilock Synth
• Electronically Chopped Amplifier
• Varying multiplication bands

Tx
Rx
sample