holger kreckel, andrew mills, manori perera, brian siller, kyle crabtree, carrie kauffman, benjamin...

Holger Kreckel, Andrew Mills, Manori Perera, Brian Siller, Kyle Crabtree, Carrie Kauffman,

Benjamin J. McCall

University of Illinois at Urbana-Champaign

SCRIBES

High Resolution Spectroscopy of Molecular Ion Beams

High Resolution Spectroscopy of Molecular Ion BeamsACS San Francisco, Mar 22nd 2010Holger Kreckel / UIUC

Herschel Space Observatory

SOFIAStratospheric Observatory for Infrared Astronomy

Upcoming observatories exploring the molecular universe


temperatures: 10-100 Kdensity: 102 - 108 cm-3

• no three-body collisions • no endothermic reactions• no reactions with barriers

Molecular clouds:places of stellar birth

Interstellar Medium: density and temperature


Ions are key!

- the UMIST database lists 4572 binary reactions, 2386 ion-neutral reactions, 552 charge exchange reactions,

- 2/3 of the reactions are ion-neutral processes, - 30% of these reactions have been measured.


Oka, Saykally Maier, Nesbitt

Ion-neutral discrimination

Low rotational temperature

Narrow linewidth

Compatible with cavity-enhanced spectroscopy

Mass spectrometry of laser-probed ions

Spectral identification of ion mass

Velocity

Modulation

Supersonic

ExpansionSCRIBES

Hollow

Cathode

Hirota, Amano

High ion column density

SensitiveCooledResolvedIonBEamSpectroscopy

Ion SpectroscopyTechniques

)(


Why Ion Beam Spectroscopy?

kinematic compressionof the linewidth

Δω ~ 1/√ Ebeam


SCRIBES setup

Overlap region

TOF mass spectrometer

particledetector

supersonic expansion source

detector

cavitymirrors

laser light

ion beam

beam modulation plates

20 cm


Ion sources

Cathode3.5 kV

Anode7.5 kV

Extraction plateGround

N2 plasma

Cold cathode discharge

Continuous Supersonic Expansion

• simple• high ion density• rotationally hot

• new development• requires heavy pumping• rotationally cold


Continuous supersonic expansion source(K Crabtree, C Kauffman)

Gas flow

O-Rings

Pinhole

Anode

Macor SpacerCathode

<100 mtorr

3 atm


Ion opticsGoal: optimize ion density in the overlap region

Overlap region

ion source

ion beam

20 cm


Output Input

Collimated beam

-V

+V

+V

-V

Diverging beam

Quadrupole vs. asymmetric cylindrical deflector

Electrostatic quadrupoles are often used as 90o deflectors


zy

zy

z

x

z xy

R2=178 mmV2=+740 V

R1=140 mmV1=-740 V

vacuum chamber

3 keV ion beam

Asymmetric cylindrical deflector


Asymmetric cylindrical deflector

xxxxxxxxxx


Ion opticsGoal: optimize ion density in the overlap region

Overlap region / 30 cm

ion source

ion beam

20 cm

ISource = 30 µA

IBeam = 10 µA

IOverlap = 2 µA

(confined by 4mm apertures,13 cm apart)

Performance with the cold cathode source:


Time of Flight Mass Spectrometer(M Perera)

Goal: characterize ion beam: composition, energy, energy spread

Overlap region

TOF mass spectrometer

ion source

ion beam

20 cm

beam modulation plates


Time of Flight measurements

N2+

N+

width ~2ns

energyspread ~ 2V

Beam energy

Voltage 3510VTOF 3560V


TOF Mass spectrometer

Source chamber

Overlap region

SCRIBES setup


Source chamber

apertures

Ti:Sa @ 925 nm

Optical Isolator

AOM

Mode Matching

Optics

FPI

-meter

EtalonFinder

detector

Spectroscopy: first tests with N2+

cw cavity ringdown spectroscopy (cw-CRDS)


•99.99% RD Mirrors

33 s time constant

min =4x10-9 cm-1

•Concentration Modulation

Beam on/ Beam off

min =5x10-10 cm-1

Reduces long term Drift

Concentration Modulation CRDS


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

CRDS / representative scans N2+


Source chamber

apertures

• Use lower finesse cavity

• Modulate the velocity of the ion beam by applying field to drift region

• Use lock in detection to further reduce noise and increase signal

PLL

pzt

detector

Next step: velocity modulation(A Mills, B Siller)


Cavity enhanced velocity modulation


Cavity enhanced velocity modulation

Siller, B, Mills, A, and McCall B.J., Optics Letters, accepted

SCRIBES / Spectroscopy with Molecular Ion Beams

Future: high resolution infrared spectroscopydifference frequency generation laser (DFG) 2.8- 4.8 µm

Ti:Sapph700 – 990 nm

532 nmpump laser

reference cavity

/2

Nd:YAG1064 nm

AOM

PPLN

/2/4

detector 2.8 – 4.8 2.8 – 4.8 μμmm

ortho-H3+ para-H3

+

ACS San Francisco, Mar 22nd 2010Holger Kreckel / UIUC

SCRIBES / Spectroscopy with Molecular Ion Beams

Source: NIST Source: Menlo Systems

Future: high resolution infrared spectroscopyMenlo Systems frequency comb

ACS San Francisco, Mar 22nd 2010Holger Kreckel / UIUC


6.6

6.4

6.2

6.0

5.8

5.6

5.4

5.2

10859.3500010859.3450010859.34000

4

3

2

1

0

Q22(14)

CEVMSFerguson 85

MHz

cm-1

0.001 cm-1

Lock

-in-s

igna

lPrecision Cavity Enhanced Velocity

Modulation of N2+ in a AC Discharge Plasma


SCRIBES

High resolution Spectroscopy with SCRIBES

Almost all the individual parts are working,Now we have to bring them all together!

DFG Laser

Expansion sourceHNN+, HCS+,HOC+,

HCO+, CO+,CH+, HCNH+, CH5

+, C3H3

+, C6H7+

etc, etc ....

Frequencycomb

Velocity modulation


NASA LaboratoryAstrophysics

NSF Divisions of Chemistry & Astronomy

Dreyfus New Faculty Award

Packard Fellowship

Air Force Young Investigator Award

Cottrell Scholarship

NSF Division of AMO Physics

Holger Kreckel, Andrew Mills, Manori Perera, Brian Siller,

Kyle Crabtree, Carrie Kauffman, Benjamin J. McCall

University of Illinois at Urbana-Champaign

Acknowledgements


Action spectroscopy of H3+ in a cryogenic ion trap

detector

ArH+H3+

He, Ar

H3+

ArH++H2 - 0.57 eV

H3+ (v=0) +Ar

H3+ (v>1) + Ar

ArH+ + H2 + X eV

E [

cm-1]

Ti:Sa Laser

α [rad]

Kreckel et al, JCP 129, 164312 (2008)


Oka, Saykally Maier, Nesbitt

Ion-neutral discrimination

Low rotational temperature

Narrow linewidth

Compatible with cavity-enhanced spectroscopy

Mass spectrometry of laser-probed ions

Spectral identification of ion mass

Velocity

Modulation

Supersonic

ExpansionSCRIBES

Hollow

Cathode

Hirota, Amano

High ion column density

SensitiveCooledResolvedIonBEamSpectroscopy

Ion SpectroscopyTechniques

)(

holger kreckel, andrew mills, manori perera, brian siller, kyle crabtree, carrie kauffman, benjamin...

Documents

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