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

High-Resolution Techniques Oka, SaykallyMaier, Nesbitt    Ion-neutral discrimination Low rotational temperature Narrow linewidth Compatible with cavity-enhanced spectroscopy Mass spectrometry of laser-probed ions Velocity Modulation Supersonic Expansion SCRIBES  Hollow Cathode Hirota, Amano High ion column density  S ensitive C ooled R esolved I on BE am S pectroscopy 

Fast Ion Beam Spectroscopy Pioneered by Saykally group, late 1980s Five (known) ions studied – HF +, HN 2 +, HCO +, H 3 O +, NH 4 + 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) velocity modulation fast ion beam HF +

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

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

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

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

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

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

Mass Spectrometry: Mass Distribution N2+N2+ N+N+ Mass Spectrometer calibrated with an air discharge. Nitrogen discharge shows mostly N 2 +, some N +. Ion current should represent N 2 + current.

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) 3.4 V, 77 MHz Short term (several minutes) 1 V, 46 MHz Long term (several hours)

June 18, 2010 Scans Measured float voltage with fast high voltage probe 3900 Beam energy measured MS 3900 V Laser scanned over V beam energy for the Q 11 (14) N 2 + blue shifted line, modulated at ± 10 Volts. Expected S/N ~(9-22). Still troubleshooting this very recent addition of spectroscopy to the ion beam S/N 1.33E E-05Signal 5.06E+06 Ion Density 3900 Float Voltage Ion Current 6.02E E-06Noise Fraction of band

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

Acknowledgments Air Force Young Investigator Award FA Visit us at: NASA Laboratory Astrophysics NSF Chemistry, Physics, Astronomy Dreyfus New Faculty, Teacher-Scholar Awards Packard Fellowship Cottrell Scholarship Sloan Fellowship