Initial Development of High Precision, High Resolution Ion Beam Spectrometer in the Near-Infrared
21
Initial Development of High Precision, High Resolution Ion Beam Spectrometer in the Near-Infrared Michael Porambo , Brian Siller, Andrew Mills, Manori Perera, Holger Kreckel, Benjamin J. McCall International Symposium on Molecular Spectroscopy The Ohio State University 18 June 2012
description
Initial Development of High Precision, High Resolution Ion Beam Spectrometer in the Near-Infrared. Michael Porambo , Brian Siller, Andrew Mills, Manori Perera, Holger Kreckel, Benjamin J. McCall International Symposium on Molecular Spectroscopy The Ohio State University 18 June 2012. - PowerPoint PPT Presentation
Transcript of Initial Development of High Precision, High Resolution Ion Beam Spectrometer in the Near-Infrared
Initial Development of High Precision, High Resolution Ion
Beam Spectrometer in the Near-Infrared
Michael Porambo, Brian Siller, Andrew Mills, Manori Perera, Holger Kreckel, Benjamin J. McCall
International Symposium on Molecular SpectroscopyThe Ohio State University
18 June 2012
Outline
• Introduction: Why a Fast Ion Beam?• Ion Beam Description• NIR Spectra• Summary and Future Work
Molecular IonsImportant in many areas of nature and science
H2+
H3+
CH+
CH2+
CH3+
CH5+
CH4
C2H3+
C2H2
C3H+
C3H3+
H2
H2
H2
H2
H2
C
e
C+
e
C+
OH+
H2O+
H3O+
H2O
OHe
O
H2
H2
HCO+
CO
HCNCH3NH2
CH3CN
C2H5CN
N, e
NH3, e
HCN, eCH3CN, e
eCO, e
H2O, e
CH3OH, e
CHCH2CO
CH3OH
CH3OCH3
CH3+
C2H5+e
C2H4
e
C3H2
e
C3H
e
C2H
AstrochemistryAtmospheric science
Fundamental physics and chemistry
CH5+
From White et al. Science, 1999, 284, 135–137.From B. J. McCall, Ph.D. Thesis, Univ. of Chicago, 2001.
NASA Picture of the Day, Expedition 13 Crew, International Space Station, NASA
Challenge: How to produce ions in the laboratory effectively to study them?
Ion Production MethodsHollow Cathode
Supersonic Expansion
Positive Column
Way to bring low rotational temperature and ion-neutral discrimination together?
No ion-neutral discrimination
Low rotational temperature
No ion-neutral discrimination
Ion-neutral discrimination with velocity modulation
No low rotational temperature
Ion Beam Spectroscopy-last attempted in 1980s–1990s1
-advances in technology open newopportunities
1Coe et al. J. Chem. Phys. 1989, 90, 3893.
Sensitive, Cooled, Resolved Ion BEam Spectroscopy – SCRIBES
TOF massspectrometer
Sourcechamber
Overlapregion
Laser incavity
Electrostatic Bender2
Rigorous ion-neutral discrimination
Can perform low temperature spectroscopy with a supersonic discharge source
Low ion densityMake up for this with cavity-enhanced spectroscopy2Kreckel et al. Rev. Sci. Instrum. 2010, 81, 063304.
Sensitive, Cooled, Resolved Ion BEam Spectroscopy – SCRIBES
Spectroscopic Detection
Noise ImmuneCavityEnhanced-OpticalHeterodyneMolecularSpectroscopy
Cavity enhancement for longer pathlength (× Finesse/π)
Spectroscopic Detection
Noise ImmuneCavityEnhanced-OpticalHeterodyneMolecularSpectroscopy
Heterodyne/Frequency Modulation Detection for Lower Noise
EOM
NICE-OHMS Signal
Spectroscopic DetectionEOM
Lock-In Amplifier
NICE-OHMS Signal
Noise ImmuneCavityEnhanced-OpticalHeterodyneMolecularSpectroscopy
Also velocity modulate the ion beam and demodulate at this signal.
Ion Beam
Doppler Splitting
nred nblue
Mass information encoded in the optical
spectrum!
First Spectroscopic Target• Obtain rovibronic spectral transitions of Meinel band
of N2+
• Near-infrared transitions probed with commercial tunable titanium–sapphire laser (700–980 nm)
• N2+ formed in cold cathode ion source; no rotational
cooling
Experimental N2+ Signal
Frequency (cm−1)
Frac
tiona
l Abs
orpt
ion
(× 1
0−7)
No absorption observed!
Absorption
Dispersion
• Absorption signal strongly attenuated by saturation.3 Not observable!• Saturation parameters: 30,000 carrier, 6300 sidebands.• Dispersion signal attenuated by a factor of 2 due to saturation.3Ma et al. J. Opt. Soc. Am. B 2008, 25, 1144–1155.
Spectral Signals
• Obtain line centers, linewidths, and amplitudes from fits• FWHM ≈ 120 MHz (at 4 kV)
From Mills et al. J. Chem. Phys. 2011, 135, 224201.
TOF MS
Mass spectrum of nitrogenic ion beam. Energy spread in inset corresponds to an expected linewidth of 120 MHz.
From Mills et al. J. Chem. Phys. 2011, 135, 224201.
Spectral Signals
• Obtain line centers, linewidths, and amplitudes from fits• FWHM ≈ 120 MHz (at 4 kV)• Noise equivalent absorption ~ 2 × 10−11 cm−1 Hz−1/2 (50× lower than last ion
beam instrument)1
• Within ~1.5 times the shot noise limit!
From Mills et al. J. Chem. Phys. 2011, 135, 224201.
1Coe et al. J. Chem. Phys. 1989, 90, 3893.
Ultra-High Resolution Spectroscopy
• Rough calibration with Bristol wavelength meter (~70 MHz precision)
• Precisely calibrate with MenloSystems optical frequency comb (<1 MHz accuracy)
Frequency Comb Calibrated Spectra
Only ~8 MHz from line center obtained in N2+ positive column work.4
Confident in improvements in the mid-IR.4Siller, B. M. et al. Opt. Express 2011, 19, 24822.
Average the line centers
Average the line centers
Summary and Conclusions• Ion Beam Spectroscopy – effective in studying
molecular ions.• High sensitivity spectroscopy used to study ion
beam – high S/N, Doppler splitting.
• Spectroscopy on rovibronic transitions of N2+ –
first direct spectroscopy of electronic transition in fast ion beam.
• Accurate frequency calibration with optical frequency comb.
Present and Future Work• Ro-vibrational spectroscopy in the mid-
IR• Integration of supersonic cooling
Stay tuned to MG05 for more information!
AcknowledgmentsMcCall Research Group Machine ShopElectronics ShopJim CoeRich SaykallySources of Funding
– Air Force – NASA– Dreyfus– Packard– NSF
– Sloan–Research Corp.– Springborn Endowment
