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Optical and NIR Photodetachment Spectroscopy in External Fields Charlotte Chapter of the OSA March 15, 2001 PowerPoint PPT Presentation


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Optical and NIR Photodetachment Spectroscopy in External Fields Charlotte Chapter of the OSA March 15, 2001. John Yukich Davidson College Department of Physics. -. -. -. +. -. -. -. -. -. +. -. -. Negative Ion Formation. Short-range attractive potential ( ~ 2 eV by a few Å )

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Optical and NIR Photodetachment Spectroscopy in External Fields Charlotte Chapter of the OSA March 15, 2001

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Optical and nir photodetachment spectroscopy in external fields charlotte chapter of the osa march 15 2001

Optical and NIRPhotodetachment Spectroscopy inExternal FieldsCharlotte Chapter of the OSAMarch 15, 2001

John Yukich

Davidson College

Department of Physics


Negative ion formation

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Negative Ion Formation

  • Short-range attractive potential ( ~ 2 eV by a few Å )

  • Electron correlation effects – responsible for covalent bonds

  • Only one or two stable, boundstates of the ion


Photodetachment

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Photodetachment

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  • X- + photon  X + e-

  • ½ of electron-atom collision

  • minimum photon energy necessary is known

  • as the “electron affinity”

  • Why study photodetachment in fields?


Photodetachment with b fields

Photodetachment with B-Fields

  • departing electron executes cyclotron motion in field

  • motion in plane perpendicular to B is quantized to cyclotron or Landau levels separated by the cyclotron frequency ω = eB/me

  • motion along axis of field is continuous, non-quantized

  • for typical B = 1.0 Tesla, ω ≈ 30 GHz, period = 36 ps

  • quantized Landau levels add structure to detachment cross section


Detachment cross section in b field

Detachment cross section in B field


Optical apparatus

Optical Apparatus

Diode seed

Diode amplifier

MOPA: 250 mW single-mode tunable

Wavemeter

to 0.02 cm-1

Spectrum

Analyzer

8 GHz FSR

Ion

trap


Detachment scan in 1 0 tesla

Detachment scan in 1.0 Tesla


Time domain spectroscopy

Time-domain spectroscopy

  • Short pulse excites multiple cyclotron levels simultaneously.

  • Wave packet of cyclotron states orbits atomic core with uniform cyclotron frequency.

  • Subsequent short pulse probes the detached portion of the electron wave function

  • Alternately: second pulse creates additional wave packet


Ramsey interferometry

Ramsey interferometry


Optical and nir photodetachment spectroscopy in external fields charlotte chapter of the osa march 15 2001

  • Multiple path interferometry

  • Phase information of first pulse is stored in the ions

  • Phase information of second pulse is then compared with that of first pulse

  • Optical memory!

What about electric fields?


Photodetachment with e fields

Photodetachment with E-Fields


Ion creation

Ion creation


Energy levels of o

Energy levels of O-


Detachment cross section field free

Detachment cross section, field-free


Ion trap

Ion trap


Ion trap detection electronics

Ion trap detection electronics


Half of the wavemeter

Half of the wavemeter


Ultrafast apparatus

Ultrafastapparatus


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