Efficient X-ray generation from gold colloidal solutions

TL;DR

This study systematically investigates hard X-ray generation from gold nanoparticle solutions, revealing a scaling law, optimal particle size, and laser conditions that maximize X-ray emission efficiency.

Contribution

It introduces a detailed analysis of X-ray generation mechanisms in gold colloidal solutions, highlighting the role of nanoparticle size and laser pulse chirp in optimizing emission.

Findings

X-ray generation scales with a 6-photon process before saturation.

Optimal X-ray emission occurs with 40 nm diameter nanoparticles.

Pre-chirped 370 fs laser pulses enhance X-ray intensity.

Abstract

Hard X-ray generation for Au nanoparticle dispersion was systematically investigated for different particle diameters ranging from 10 to 100 nm with a narrow size distribution of +/- 2%. Scaling law of X-ray generation is close to a 6-photon process before the onset of saturation for excitation by 45 fs laser pulses with central wavelength of 800 nm. This is consistent with bulk plasmon excitation at wavelength ~ 138 nm. The longitudinal E-field component due to nanoparticle focusing is responsible for the excitation of the longitudinal bulk plasmon. The proposed analysis also explains X-ray emission from water breakdown via an electron solvation mechanism at ~6.2 eV. The most efficient emission of X-rays was observed for 40 +/- 10 nm diameter nanoparticles which also had the strongest UV extinction. X-ray emission was the most efficient when induced by pre-chirped 370 +/- 20 fs laser pulses and exhibited the highest intensity at a negative chirp.