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Fast Beams of Neutral Molecules: The Next Generation of Laser-Induced Molecular Dissociation Imaging

Explore the cutting-edge research on laser-induced molecular dissociation imaging using fast beams of neutral molecules. Learn about the motivations, theories, and practical applications involved in this innovative field. Discover the process of neutralizing fast ions to create fast neutrals for imaging purposes. Gain insights into target selection, cross-section measurements, and the use of microchannel plates in the experimental setup. Follow the next steps in testing and optimizing the process for efficient molecular dissociation imaging. Acknowledgments to KSU, Dr. Itzik Ben-Itzhak, IBI Group, and the National Science Foundation.

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Fast Beams of Neutral Molecules: The Next Generation of Laser-Induced Molecular Dissociation Imaging

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  1. Fast beams of neutral molecules –the next generation of laser induced molecular dissociation imaging Drew Rotunno Mentor: Dr. Itzik Ben-Itzhak, Bethany Joachim

  2. Motivations • AMO – Atomic and Molecular Collisions DETECTOR

  3. Motivations • AMO – Femtosecond laser pulses • Laser-induced molecular dissociation imaging DETECTOR

  4. Motivations • Laser + Target Neutrals • Not enough energy to detect DETECTOR DETECTOR E

  5. Motivations • Laser + Fast Neutrals DETECTOR

  6. Motivations • Q: How do we get fast neutrals? • A: Neutralize fast ions

  7. How do we neutralize? • Remove an electron from a negatively charged ion • Add an electron to a positively charged ion e

  8. Target Choice Noble Gasses • Argon (jet, cell) • Ionization energy • ~15eV / atom • vs. Alkali ~5eV • Very cheap • and available • and safe

  9. The Theory H+ H2+ Ar H2+ H2 (H2*)

  10. Cross sections • Collision probability, reinterpreted as area • Depends on species, both target and projectile • Depends on Beam energy

  11. Measurements of Cross sections H2+ + Ar, separated by product Charge transfer from Cs, by projectile A.V. Phelps (1992) F.W. Meyer et al. (1977)

  12. Conversion rates Yield (H2) Cross Section Number of incoming particles (H2+) Target particles per unit volume Length

  13. Conversion rates Want 10% for few keV H2+ on Ar ~ 3 cm ? Solving for target density shows we need about At STP, this means we need 1 mTorr= .001 mmHg of pressure

  14. The Theory H+ H2+ Ar H2+ H2 (H2*)

  15. The Piece diameter ~ 2 inches

  16. The Cut-away MicroChannel Plate Argon gas in

  17. The Microchannel Plate

  18. The Cut-away “Gas Mask” MicroChannel Plate Argon gas in

  19. Fluid Flow Through Tubes • Higher length/radius ratio leads to more directed flow • Preserves vacuum • Ours: L/R ~ 80 W. Steckelmacher et al. (1978)

  20. Test Beamline

  21. Next Step - Testing • Measuring conversion factor • How much H2 do we get? ( H fragments too) • Maximize • Fast feedback to optimize pressure • Too high – double collisions, more H fragments • States of molecules • Populations of ground vs. excited states • Hard to determine, but interesting to study

  22. End Thanks KSU, Dr. Itzik Ben-Itzhak, IBI Group, National Science Foundation

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