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Mid-Infrared NICE-OHMS Spectrometer for the Study of Cold Molecular Ions

Mid-Infrared NICE-OHMS Spectrometer for the Study of Cold Molecular Ions. . Michael Porambo , Jessica Pearson, Courtney Talicska , Benjamin J. McCall ISMS June 18, 2014 WG12. Outline. Background and Motivation Spectrometer/Instrumentation Present and Future Work.

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Mid-Infrared NICE-OHMS Spectrometer for the Study of Cold Molecular Ions

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  1. Mid-Infrared NICE-OHMS Spectrometer for the Study of Cold Molecular Ions . Michael Porambo, Jessica Pearson, Courtney Talicska, Benjamin J. McCall ISMS June 18, 2014 WG12

  2. Outline • Background and Motivation • Spectrometer/Instrumentation • Present and Future Work

  3. Why molecular ions?Why spectroscopy?

  4. Combustion Efficiency of engines† JanneKaraste, http://commons.wikimedia.org/wiki/File:Midsummer_bonfire_closeup.jpg http://www.navy.mil/view_single.asp?id=40674 †Thomas, Mass Spec. Rev., 2008, 27, 485–530.

  5. Interstellar Reactions Atmospheric Chemistry • Resolved, high precision spectroscopy to study these fields All molecular models drawn in Avogado (http://avogadro.cc/wiki/Main_Page) http://earthobservatory.nasa.gov/IOTD/view.php?id=7373

  6. Laboratory Astrochemistry ESO/C. Malin, http://www.eso.org/public/images/ann13016a/ Complex, congested spectra from interstellar medium Better understanding of the ISM (e.g., detection of more molecules) Simpler, standard spectra from lab of hypothesized molecules

  7. Challenges • Low number density • Small fraction of ions compared to neutrals • High rotational temperature

  8. Overcoming Low Number Density • Cavity enhancement to increase signal • Heterodyne/frequency modulation spectroscopy to decrease noise EOM

  9. Heterodyne/Frequency Modulation

  10. Heterodyne/Frequency Modulation EOM 113 MHz FMS Signal 113 MHz EOM Relative Frequency (MHz) Relative Frequency (MHz)

  11. NICE-OHMS Cavity Enhancement Noise Immune Cavity-Enhanced Optical Heterodyne Molecular Spectroscopy (NICE-OHMS)† Heterodyne/Frequency Modulation EOM †Ye et al., JOSA B, 1998, 15, 6–15.

  12. Sideband Spacing Cavity Longitudinal Modes Laser Spectrum Spectroscopy sidebands must couple into longitudinal modes

  13. NICE-OHMS/NICE-OHVMS Projects Plasma discharge Other talks: MK06 FA01 Supersonic expansion Overcoming high rotational temperature

  14. Continuous Supersonic Expansion Discharge Source 100 mTorr chamber pressure High pressure in line (≈2 atm) Low temperature ions Tiny pinhole (0.5 mm diameter) Source running with nitrogen (N2+discharge) H3+ temperature: 80–110 K† Spectroscopy of this “zone of silence” †Crabtree et al., Rev. Sci. Instrum., 2010, 81, 086103.

  15. Difference Frequency Generation 2.8–4.8 µm PPLN Ti:Sapph (700–1100 nm) EOM Nd:YAG (1064 nm)

  16. Mid-IR NICE-OHMS Spectrometer One of the first broadly tunable mid-IR NICE-OHMS spectrometers† NICE-OHMS Signal Difference Frequency Generation setup To EOM RF Generator (113 MHz) †Porambo et al., Opt. Lett., 2012, 37, 4422–4424.

  17. Mid-IR NICE-OHMS Spectrometer IGBT Switching Circuit Lock-In Amplifier Function Generator (1–10 kHz) Difference Frequency Generation setup To EOM RF Generator (113 MHz)

  18. 1-10 kHz Source Opto-Isolator V+ 15 V Power Supply V- V2 V1 IGBT Driver IGBT GND2 GND1 Out In V Out In GND DC/DC Isolator +Vout +Vin -Vout -Vin Insulated-Gate Bipolar Transistor (IGBT) Switching Circuit -1 kV Adapted from diagram by Thomas Houlahan, Jr.

  19. 13000 m3/hr Roots blower system

  20. Temperature Determination with Methane ln (I/S) Lower State Energy (cm-1) Estimated methane rotational temperature of 300±28 K

  21. Present and Future Work • H3+ spectroscopy to test temperature of ion • HN2+ spectroscopy to test efficient cooling • High precision spectroscopy of ions of astrochemical/fundamental interest

  22. High Precision Spectroscopy Difference Frequency Generation setup (2.8–4.8 µm) Optical Frequency Comb H2CO+ C3H3+

  23. Summary • Molecular ions key in combustion, atmospheric, interstellar reactions • Challenging to study, but overcome with NICE-OHMS on supersonic expansion discharge source • Preliminary temperature determinations promising; ultimate goal is precision spectroscopy of cooled ions

  24. Acknowledgments Thomas Houlahan, Jr. Springborn Endowment, UIUC NASA Earth and Space Science Fellowship

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