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Charles R. Markus, Adam J. Perry, James N. Hodges, Benjamin J. McCall
Improved Spectroscopy of Molecular Ions in the Mid-Infrared with Up-Conversion Detection Charles R. Markus, Adam J. Perry, James N. Hodges, Benjamin J. McCall 71st International Symposium on Molecular Spectroscopy University of Illinois at Urbana-Champaign 21 June, 2016 TC07
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Overview NICE-OHVMS technique Removing parasitic etalons
Description Limitations Removing parasitic etalons Mechanism of detection Brewster-Spoiler plate Up-conversion detection Design Results Future directions
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Molecular Ions H Over 190 molecules identified in the interstellar medium (ISM) Reactions must overcome cold and diffuse environment Ion-neutral reactions dominate chemistry of ISM Aleman, et al., A&A,2014, 566, A79. πm πm
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Molecular Ions H Many of the simplest molecules are molecular ions Accurate ab initio calculations must go beyond Born-Oppenheimer approximation Laboratory spectra act as benchmarks for state-of-the-art methods H He H
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Ion Spectroscopy Ion are orders of magnitude less abundant than neutral species
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NICE-OHVMS Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy
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Increased Signal and Precision
NICE-OHVMS Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy Increased Signal and Precision K. N. Crabtree, et al., Chem. Phys. Lett., 2012, 551, 1-6.
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Increased Signal and Precision
NICE-OHVMS Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy Increased Signal and Precision Improved Sensitivity K. N. Crabtree, et al., Chem. Phys. Lett., 2012, 551, 1-6.
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Increased Signal and Precision Ion-Neutral Discrimination
NICE-OHVMS Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy Increased Signal and Precision Ion-Neutral Discrimination Improved Sensitivity K. N. Crabtree, et al., Chem. Phys. Lett., 2012, 551, 1-6.
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Velocity Modulation Velocity
C. S. Gudeman, et al., J. Chem. Phys., 1983, 78, 5873.
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- - + + Velocity Modulation Velocity Lock-in Amplifier
C. S. Gudeman, et al., J. Chem. Phys., 1983, 78, 5873.
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- - + + Velocity Modulation Velocity Lock-in Amplifier
B. M. Siller, et al., Opt. Lett., 2010, 35, 1266.
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- - + + Velocity Modulation π Lock-in Amplifier Lock-in Amplifier
Referenced at 2Γπ π B. M. Siller, et al., Opt. Lett., 2010, 35, 1266
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Cavity Enhancement Signal increase of 2F/π FSR =π/2ππ πΌ π‘ππππ π
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Heterodyne Detection
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NICE-OHMS πΌ π‘ππππ π Fheterodyne = nΓFSR
J.Ye, et al., J. Opt. Soc. Am. B, 1998, 15, 6.
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Saturation Spectroscopy
πβ π πππ π‘ (MHz) Velocity (m/s)
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Saturation Spectroscopy
πβ π πππ π‘ (MHz) Velocity (m/s)
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Saturation Spectroscopy
πβ π πππ π‘ (MHz) Velocity (m/s)
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Saturation Spectroscopy
πβ π πππ π‘ (MHz) Velocity (m/s)
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Saturation Spectroscopy
πβ π πππ π‘ (MHz) Velocity (m/s)
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Saturation Spectroscopy
πβ π πππ π‘ (MHz) Velocity (m/s)
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NICE-OHVMS Spectrometer
Frequency Calibration 40 kHz to PZT OPO PZT nidler = npump - nsignal ~3 MHz EOM Lock-In Amplifier Lock-In Amplifier Ξ½ 2xf = 80 kHz 80 MHz YDFL X & Y Channels X & Y Channels 90o Phase Shift Fast Lock Box Slow B. M. Siller, et al., Opt. Express,2011, 19,
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NICE-OHVMS Results H3+ R(1,0), 2725.898 cm-1 80 MHz Mixer 1 Mixer 2
2Γ40 kHz Lock-in 1 Lock-in 2 0o 90o Mixer 1 Output Mixer 2 Output H3+ R(1,0), cm-1
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Parasitic Etalons π πΌ π πΌ π πΌ FSR = π 2ππ π π‘ =πΌΓsinβ‘(2 π π£ππ π‘)
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Spoiling Parasitic Etalons
π πΌ
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Spoiling Parasitic Etalons
π πΌ C. Webster, et al., J. Opt. Soc. Am., 1985, 2, 1464.
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Spoiling Parasitic Etalons
Mixer 1 Output H3+ R(1,0), cm-1 Mixer 2 Output Galvo S/N (best channel) Off 25 On 763 Galvo S/N (best channel) Off 25
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Heterodyne Detection π π»ππ‘ = 20% FWHM Overlapping sub-Doppler features
Optimized signal Resolved Lamb dips Improved fits Improved Ξπ
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Difference Frequency Generation
π π·πΉπΊ = 0.5% /W532 APD V10 Vigo PVM-10.6 Menlo APD 220 Ξπ 150 (MHz) 1000 MHz NEP 4800 (pW/Hz1/2) 0.4 (pW/Hz1/2) Vigo PVM-10.6 Ξπ 150 (MHz) NEP 4800 (pW/Hz1/2) Vigo PVM-10.6 Menlo APD 220 Ξπ 150 (MHz) 1000 MHz NEP 4800 (pW/Hz1/2) 0.4 (pW/Hz1/2) NEP/( π π·πΉπΊ Γ π ππ’ππ ) 10 (pW/Hz1/2)
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Up-conversion Results
H3+ R(1,0), cm-1 Mixer 1 Output Mixer 2 Output Detection Method S/N (Best Channel) 78 MHz mid-IR 337 78 MHz up-conversion 2029 390 MHz up-conversion 1211 Detection Method S/N (Best Channel) 78 MHz mid-IR 337 Detection Method S/N (Best Channel) 78 MHz mid-IR 337 78 MHz up-conversion 2029
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Up-conversion Results
4.2Γ 10 β9 cm-1 3.5Γ 10 β10 cm-1 Detection Method 78 MHz mid-IR 78 MHz up-conversion 390 MHz up-conversion 1.6Γ 10 β10 cm-1
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Future Directions H Apply up-conversion to survey of H3+
Measure fundamental band (3 β 4.5 πm) Hotband transitions Extend to measure overtone transitions (1.9 β 2.1 πm) Observe resolved Lamb dips Increase intracavity power Lock sidebands using DeVoe-Brewer locking H Ξ½ (c m β1 )
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Conclusions Removed parasitic etalons in NICE-OHVMS experiment with Brewster-spoiler plate Improved sensitivity by an order of magnitude with DFG up-conversion of mid-IR beam
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Acknowledgments Advisor: Ben McCall Special thanks to: James Hodges
Adam Perry G. Stephen Kocheril
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