Characterization of an aerosolized nanoparticle beam beyond the diffraction limit through strong field ionization

TL;DR

This paper introduces a novel strong field ionization technique for characterizing nanoparticle beams beyond the diffraction limit, enabling direct density measurements and beam optimization.

Contribution

The study presents a new method using ultrafast laser ionization to analyze nanoparticle beams, overcoming limitations of light scattering detection for particles smaller than 10 nm.

Findings

Effective detection of 10 nm nanoparticles.

Ability to map 3D particle density distribution.

Beam density and width can be optimized via gas flow control.

Abstract

The study of nanomaterials is an active area of research for technological applications as well as fundamental science. A common method for studying properties of isolated nanoparticles is by an in-vacuum particle beam produced via an aerodynamic lens. Despite being common practice, characterization of such beams has proven difficult as light scattering detection techniques fail for particles with sizes beyond the diffraction limit. Here we present a new technique for characterizing such nanoparticle beams using strong field ionization. By focusing an ultrafast, mJ-level laser into the particle beam, a nanoparticle within the laser focus is ionized and easily detected by its ejected electrons. This method gives direct access to the nanoparticle density at the location of the focus and, by scanning the focus through the transverse and longitudinal profiles of the particle beam, the 3-dimensional particle density distribution can be attained. Further, we show that strong field ionization is effective in detecting spherical nanoparticles as small as 10 nm in diameter. Additionally, this technique is an effective tool in optimizing the particle beam for specific applications. As an example we show that the particle beam density and width can be manipulated by restricting the gas flow into the aerodynamic lens.