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

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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  1. Optical and NIRPhotodetachment Spectroscopy inExternal FieldsCharlotte Chapter of the OSAMarch 15, 2001 John Yukich Davidson College Department of Physics

  2. - - - + - - - - - + - - 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

  3. - - - - + - - Photodetachment - - + - - • X- + photon  X + e- • ½ of electron-atom collision • minimum photon energy necessary is known • as the “electron affinity” • Why study photodetachment in fields?

  4. 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

  5. Detachment cross section in B field

  6. 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

  7. Detachment scan in 1.0 Tesla

  8. 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

  9. Ramsey interferometry

  10. 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?

  11. Photodetachment with E-Fields

  12. Ion creation

  13. Energy levels of O-

  14. Detachment cross section, field-free

  15. Ion trap

  16. Ion trap detection electronics

  17. Half of the wavemeter

  18. Ultrafastapparatus

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