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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 NIRPhotodetachment Spectroscopy inExternal FieldsCharlotte Chapter of the OSAMarch 15, 2001

John Yukich

Davidson College

Department of Physics


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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


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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

  • 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


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


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


  • 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


Ion creation


Energy levels of O-


Detachment cross section, field-free


Ion trap


Ion trap detection electronics


Half of the wavemeter


Ultrafastapparatus


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