Abstract
Aerosol nanoparticle injectors are fundamentally important for experiments where container-free sample handling is needed to study isolated nanoparticles. The injector consists of a nebuliser, a differential pumping unit, and an aerodynamic lens to create and deliver a focused particle beam to the interaction point inside a vacuum chamber. The tightest focus of the particle beam is close to the injector tip. The density of the focusing carrier gas is high at this point. We show here how this gas interacts with a near infrared laser pulse (800 nm wavelength, 120 fs pulse duration) at intensities approaching 1016 Wcm−2. We observe acceleration of gas ions to kinetic energies of 100s eV and study their energies as a function of the carrier gas density. Our results indicate that field ionisation by the intense near-infrared laser pulse opens up a plasma channel behind the laser pulse. The observations can be understood in terms of a Coulomb explosion of the created underdense plasma channel. The results can be used to estimate gas background in experiments with the injector and they open up opportunities for a new class of studies on electron and ion dynamics in nanoparticles surrounded by a low-density gas.
Highlights
We present a theoretical model showing that the electrons, which are field-ionised by the strong NIR laser field, are driven out of the focus by the laser ponderomotive forces and a channel of underdense plasma is formed behind the pulse
We calculate the explosion of the plasma channel in two steps: (i) We perform particle-in-cell (PIC) simulations of electrons driven by the laser field to show the channel formation and obtain parameters of the channel
We have performed an extensive study on ion emission from NIR laser-irradiated gases injected into a vacuum chamber through a gas dynamic virtual nozzle (GDVN) combined with an aerodynamic lens stack (ALS)
Summary
The development of laser light sources with high intensity ultrashort pulses has opened up new possibilities in science, from the study of structure and dynamics in structural and molecular biology[1,2,3,4,5,6,7] to detailed studies of ionization/excitation processes in atoms/molecules[8,9,10,11,12,13], to investigations of matter under extreme conditions[14,15,16,17]. We show that after irradiation with a strong NIR laser pulse a plasma channel is formed in the interaction region where ions (coming both from the injector carrier gas and from the background gas in the chamber) are accelerated by Coulomb forces.
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