Facile time-of-flight methods for characterizing pulsed superfluid helium droplet beams

Area of Science:

• Atomic and Molecular Physics
• Physical Chemistry
• Materials Science

Background:

• Superfluid helium droplets are crucial for studying quantum phenomena and as nanoreactors.
• Characterizing droplet beams is essential for sensitive measurements like electron diffraction.
• Existing methods for droplet detection can be complex or lack sensitivity.

Purpose of the Study:

• To present two facile time-of-flight (TOF) methods for detecting superfluid helium droplets and dopants.
• To characterize the Even-Lavie cryogenic pulsed valve using these TOF methods.
• To analyze droplet properties, including size, speed, and dopant pickup efficiency.

Main Methods:

• Electron impact ionization time-of-flight mass spectrometry for helium cluster detection.
• Multiphoton non-resonant laser ionization for dopant fragment cluster detection.
• Utilizing a 266 nm laser for dopant ionization and a heated filament for electron impact ionization.

Main Results:

• Resolved ionized helium clusters (He2+, He4+) indicating superfluid droplets.
• Generated complex cluster ions of dopant fragments with helium atoms.
• Observed distinct primary (larger, slower) and rebound (smaller, faster) droplet pulses.
• Found higher dopant pickup efficiency for the primary pulse above 13 K nozzle temperature.
• Determined a total doped droplet pulse duration of approximately 20 μs.

Conclusions:

• The developed TOF methods provide facile and sensitive detection of superfluid helium droplets and doped clusters.
• Characterization of the Even-Lavie valve revealed distinct droplet pulse characteristics.
• The findings highlight the importance of rapid droplet beam characterization for advanced experimental techniques.