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Towards High Resolution Cavity Enhanced Spectroscopy with Fast ion Beams

Towards High Resolution Cavity Enhanced Spectroscopy with Fast ion Beams. Andrew Mills, Brian Siller, Manori Perera, Holger Kreckel, Ben McCall. High-Resolution Techniques. S ensitive C ooled R esolved I on BE am S pectroscopy. Hirota, Amano. Oka, Saykally. Maier, Nesbitt. Supersonic

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Towards High Resolution Cavity Enhanced Spectroscopy with Fast ion Beams

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  1. Towards High Resolution Cavity Enhanced Spectroscopy with Fast ion Beams Andrew Mills, Brian Siller, Manori Perera, Holger Kreckel, Ben McCall

  2. High-Resolution Techniques Sensitive Cooled Resolved Ion BEam Spectroscopy Hirota, Amano Oka, Saykally Maier, Nesbitt Supersonic Expansion Velocity Modulation Hollow Cathode SCRIBES     High ion column density     Ion-neutral discrimination       Low rotational temperature       Narrow linewidth    Compatible with cavity-enhanced spectroscopy   Mass spectrometry of laser-probed ions

  3. Fast Ion Beam Spectroscopy velocity modulation fast ion beam HF+ • Pioneered by Saykally group, late 1980s • Five (known) ions studied • HF+, HN2+, HCO+, H3O+, NH4+ • Abandoned in early 1990s • Struggles: • ions still at high temperature • low ion column density • problems with infrared laser • New approaches: • supersonic ion source • high-sensitivity spectroscopy • difference frequency laser Coe et al., JCP 90, 3893 (1989)

  4. SCRIBES OSU 2009 Cylindrical Bender Cold Cathode Source Beam Modulated Time of Flight Mass Spectrometer Not at Same Time as Spectroscopy

  5. SCRIBES OSU 2009 differential pumping beam modulated time of flight (removed for spectroscopy) movable apertures

  6. Cavity Ringdown Spectroscopy • “CW” cavity ringdown with Ti:Sapphire laser • Beam modulation (on/off) reduces long-term drift x10-9 Absorbance (cm-1) amin ~ 4.5 x 10-10 cm-1 Wavelength (nm)

  7. SCRIBES @ OSU 2010 • Removed ion beam machine from laser table • reduce vibration from pumps • Higher sensitivity spectroscopy • separate cavity from ion beam machine • cavity-locked spectroscopy • Simultaneous laser and mass spectroscopy • verify mass distribution • verify absolute beam energy (Doppler shift) • fast high voltage probe

  8. SCRIBES, OSU 2010 external cavity on floating optics bench separate support structure on wheels

  9. Cavity-Enhanced Velocity Modulation Excursion to test Spectroscopy FD2 PZT Lock-in Amplifier Ti:Sapph slow Lockbox fast EOM QWP AOM PDH: Drever, Hall, Kowalski, Hough, Ford, Munley, Applied Physics B-31 (1983) 97–105.

  10. Mass Spectrometry: Mass Distribution • Mass Spectrometer calibrated with an air discharge. • Nitrogen discharge shows mostly N2+, some N+. • Ion current should represent N2+ current. N+ N2+

  11. Mass Spectrometry: Energy Shift • Measured time over many measurements • Day to day variation • Does not match the output of the power supply • (3900 vs 3817) Long term (several hours) Short term (several minutes) 1 V, 46 MHz 3.4 V, 77 MHz

  12. June 18, 2010 Scans • Measured float voltage with fast high voltage probe 3900 • Beam energy measured MS 3900 V • Laser scanned over 3880-3960V beam energy for the Q11(14) N2+ blue shifted line, modulated at ± 10 Volts. • Expected S/N ~(9-22). • Still troubleshooting this very recent addition of spectroscopy to the ion beam 16 17

  13. Conclusions • A laser-table independent ion beam instrument has been constructed with well collimated ion beam collinear to a laser beam. • The ion beam allows for simultaneous monitoring of the beam energy prior to spectroscopy. • The output of the power supply monitor voltage is not accurate enough and the mass spectrometer must be used to determine the beam energy. • Preliminary scans have been performed, and we are continuing to search for a signal. 16 17

  14. Acknowledgments Dreyfus New Faculty, Teacher-Scholar Awards NASA Laboratory Astrophysics NSF Chemistry, Physics, Astronomy Packard Fellowship Cottrell Scholarship Sloan Fellowship Air Force Young Investigator Award FA 9550-07-1-0128 Visit us at: http://bjm.scs.uiuc.edu

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