High Precision Mid-IR Spectroscopy of 12C16O2
[1001,0201]I ← 0000 Band Near 2.7 µm
Jow-Tsong Shy
Department of Physics, National Tsing Hua
University, Hsinchu, Taiwan
Motivation and Goal
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[1001,0201]I ← 0000 and [1001,0201]II ← 0000 bands near
2.7 µm are two important absorption bands in atmosphere
Urban’s group has made heterodyne frequency
measurements for 9 transitions with an accuracy of 600
kHz in 1991.
Our goal is to provide more accurate measurements
Experimental Set-up
Experimental Scheme
Ti:sapphire Laser Side Fringe
Locking to a Stable Cavity
Frequency stability: 10 kHz; Frequency drift <100 kHz/hr
Offset Locking of Nd:YAG Laser
U. Shunemann et al., Rev. Sci. Instrum. 70, 242 (1999)
Saturated 4.3 μm Fluorescence
Longitudinal Fluorescence Cell
Used in frequency stabilization of CO2 laser previously
Direct Detection vs.
Fluorescence Detection
Direct Detection
Fluorescence Detection
Advantages of Saturated
Fluorescence Detection
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Zero background
Higher S/N
No interference fringes
Second Harmonic Demodulated
Spectrum
P = 20 mTorr
FWHM = 1.5 MHz
Urban’s Spectrum
Uncertainty
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OFC
Iodine stabilized of Nd:YAG laser
Nd:YAG laser offset locking
Ti:sapphire laser locking
Fitting error
Uncertainty 40 kHz
5 kHz
10 kHz
10kHz
10 kHz
5 kHz
Observed Transitions – P lines
Observed Transitions – R lines
19 transitions measured to 40 kHz accuracy
Molecular Constants
Molecular Constants Comparison
Comparison between observed
and calculated frequencies
Standard deviation = 46 kHz
Summary
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19 transitions have been measured to an
accuracy of 40 kHz
Accurate molecular constants of the
[1001,0201]I vibrational level have been
determined
Future Works
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Improve the collection efficiency of the
longitudinal florescence cell (X 10)
More measurements on [1001,0201]I ← 0000
band
New measurements on [1001,0201]II ← 0000
band
Acknowledgement
DFG and OFC systems
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Chun-Chieh Liao
Kuo-Yu Wu
Yu-Hung Lien
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Che-Chung Chou
Molecular constants fitting
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Carry out all measurements
$$ NSC & MOE of Taiwan