Initial Development of High Precision, High Resolution Ion - PowerPoint Presentation

Slide1

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 2012Slide2

Outline

Introduction: Why a Fast Ion Beam?

Ion Beam Description

NIR Spectra

Summary and Future WorkSlide3

Molecular Ions

Important in many areas of nature and science

H

2

+

H

3

+

CH

+

CH2+

CH3+

CH5+

CH4

C2H3+

C2H2

C3H+

C3H3+

H

2

H

2

H

2

H

2

H

2

C

e

C

+

e

C

+

OH

+

H

2

O+

H3O+

H2O

OH

e

O

H

2

H

2

HCO

+

CO

HCN

CH

3

NH

2

CH

3

CN

C

2

H5CN

N, e

NH3, e

HCN, e

CH3CN, e

e

CO, e

H

2

O, e

CH

3

OH, e

CH

CH2CO

CH3OH

CH3OCH3

CH

3+

C2H5+

e

C

2H4

e

C

3H2

e

C

3H

e

C

2H

Astrochemistry

Atmospheric science

Fundamental physics and chemistry

CH

5+

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?Slide4

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–1990s

1-advances in technology open newopportunities

1Coe et al. J. Chem. Phys. 1989

, 90, 3893.Slide5

Sensitive, Cooled, Resolved Ion BEam Spectroscopy – SCRIBES

TOF mass

spectrometer

Source

chamber

Overlap

region

Laser in

cavity

Electrostatic Bender

2

Rigorous ion-neutral discrimination

Can perform low temperature spectroscopy with a supersonic discharge source

Low ion density

Make up for this with cavity-enhanced spectroscopy

2

Kreckel

et al.

Rev. Sci.

Instrum

.

2010

,

81,

063304.Slide6

Sensitive, Cooled, Resolved Ion BEam Spectroscopy – SCRIBESSlide7
Slide8

Spectroscopic Detection

N

oise

I

mmune

C

avity

E

nhanced

-

O

ptical

H

eterodyne

M

olecularSpectroscopy

Cavity enhancement for longer pathlength (× Finesse/

π)Slide9

Spectroscopic Detection

N

oise

I

mmune

C

avity

E

nhanced

-

O

ptical

H

eterodyne

M

olecular

SpectroscopyHeterodyne/Frequency Modulation Detection for Lower Noise

EOM

NICE-OHMS SignalSlide10

Spectroscopic Detection

EOM

Lock-In Amplifier

NICE-OHMS Signal

N

oise

I

mmune

C

avity

E

nhanced

-

O

ptical

H

eterodyne

M

olecular

S

pectroscopy

Also velocity modulate the ion beam and demodulate at this signal.Slide11

Ion Beam

Doppler Splitting

Ion Beam

n

red

n

blue

Mass information encoded in the optical spectrum!Slide12
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 coolingSlide13
Experimental N

2+ SignalFrequency (cm−1)

Fractional Absorption (

× 10

−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.Slide14

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. Slide15
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. Slide16

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.Slide17
Ultra-High Resolution Spectroscopy

Rough calibration with Bristol wavelength meter (~70 MHz precision)Precisely calibrate with MenloSystems optical frequency comb (

<1 MHz accuracy

)Slide18

Frequency Comb Calibrated Spectra

Only ~8 MHz from line center obtained in N

2

+

positive column work.

4

Confident in improvements in the mid-IR.

4

Siller, B. M. et al.

Opt. Express

2011, 19

, 24822.Average the line centers

Average the line centersSlide19

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 N

2

+

–

first direct spectroscopy of electronic transition in fast ion beam.

Accurate frequency calibration with optical frequency comb.Slide20

Present and Future Work

Ro-vibrational

spectroscopy in the

mid-IR

Integration of supersonic cooling

Stay tuned to MG05 for more information!Slide21
Acknowledgments

McCall Research Group Machine ShopElectronics ShopJim CoeRich SaykallySources of FundingAir Force NASA

Dreyfus

Packard

NSF

Sloan

Research Corp.

Springborn Endowment