Towards High Resolution Cavity Enhanced Spectroscopy with Fast ion Beams Andrew Mills, Brian Siller,...
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Transcript of Towards High Resolution Cavity Enhanced Spectroscopy with Fast ion Beams Andrew Mills, Brian Siller,...
![Page 1: Towards High Resolution Cavity Enhanced Spectroscopy with Fast ion Beams Andrew Mills, Brian Siller, Manori Perera, Holger Kreckel, Ben McCall.](https://reader030.fdocuments.us/reader030/viewer/2022032804/56649e4f5503460f94b45dd6/html5/thumbnails/1.jpg)
Towards High Resolution Cavity Enhanced Spectroscopy with Fast ion Beams
Andrew Mills, Brian Siller, Manori Perera, Holger Kreckel, Ben McCall
![Page 2: Towards High Resolution Cavity Enhanced Spectroscopy with Fast ion Beams Andrew Mills, Brian Siller, Manori Perera, Holger Kreckel, Ben McCall.](https://reader030.fdocuments.us/reader030/viewer/2022032804/56649e4f5503460f94b45dd6/html5/thumbnails/2.jpg)
High-Resolution Techniques
Oka, Saykally Maier, Nesbitt
Ion-neutral discrimination
Low rotational temperature
Narrow linewidth
Compatible with cavity-enhanced spectroscopy
Mass spectrometry of laser-probed ions
Velocity
Modulation
Supersonic
ExpansionSCRIBES
Hollow
Cathode
Hirota, Amano
High ion column density
SensitiveCooledResolvedIonBEamSpectroscopy
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Fast Ion Beam Spectroscopy
• 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)
velocitymodulation
fast ionbeamHF+
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SCRIBES OSU 2009
Cold CathodeSource
CylindricalBender
Beam Modulated Time of FlightMass Spectrometer Not at Same Time
as Spectroscopy
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SCRIBES OSU 2009 differential pumping
movable apertures
beam modulatedtime of flight(removed forspectroscopy)
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924.410924.409924.408924.407924.406924.405
1.0
0.8
0.6
0.4
0.2
20
15
10
5
0
-5
-10
x10-9
min ~ 4.5 x 10-10 cm-1
Wavelength (nm)
Abs
orba
nce
(cm
-1)
x10-9
Cavity Ringdown Spectroscopy• “CW” cavity ringdown with Ti:Sapphire laser• Beam modulation (on/off) reduces long-term drift
frequencyvelocityVbeam
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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
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SCRIBES, OSU 2010
separate support structure on wheels
external cavity on floating optics bench
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Cavity-Enhanced Velocity Modulation
Lockbox
PZT
EOM
Ti:Sapph
Lock-in Amplifie
r
QWPAOM
fast
slow
PDH: Drever, Hall, Kowalski, Hough, Ford, Munley, Applied Physics B-31 (1983) 97–105.
Excursion to test Spectroscopy FD2
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Mass Spectrometry: Mass Distribution
N2+
N+•Mass Spectrometer calibrated with an air discharge.
•Nitrogen discharge shows mostly N2
+, some N+.
•Ion current should represent N2
+ current.
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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 MHzShort term (several minutes)
1 V, 46 MHzLong term (several hours)
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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
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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.
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Acknowledgments
Air Force Young Investigator AwardFA 9550-07-1-0128
Visit us at: http://bjm.scs.uiuc.edu
NASA LaboratoryAstrophysics
NSF Chemistry, Physics, Astronomy
Dreyfus New Faculty, Teacher-Scholar
Awards
Packard Fellowship
CottrellScholarship
SloanFellowship