Femtosecond Laser-Induced X-Ray Emission from Gold Nano-Colloidal Solutions

摘要

By irradiating droplets of chloroauric acid aqueous solution (~10~(-3)mol/l) and those of gold nano-colloidal solution with near-IR (～800 nm) femtosecond (35 fs) laser light, the X-ray intensity and the X-ray emission spectra were recorded. The laser pulses were focused onto the surface of droplets (～90μm in diameter) ejected from an ink-jet nozzle by an off-axis parabolic mirror. The X-ray intensity was about 660 times higher with the gold nano-colloidal solution than with the chloroauric acid aqueous solution. Electron temperatures calculated from the X-ray emission spectra on the basis of the assumption of the Boltzmann distribution were 0.074 keV for the chloroauric acid aqueous solution and 2.9 keV for the gold nano-colloidal solution. The significantly high X-ray intensity and electron temperature obtained with the gold nano-colloidal solution can be ascribed to the enhancement of the laser field intensity by surface plasmon resonance at the gold nano-particles.