High-order harmonic generation in a plasma plume of in situ laser-produced silver nanoparticles

The results of the experimental study of high-order harmonic generation (HHG) from the interaction of 45-fs Ti:sapphire laser pulses with plasma plumes of Ag nanoparticles produced in situ are presented in this article. The nanoparticles were generated by the interaction of 300-ps, 20-mJ laser pulses with bulk silver targets at an intensity of $~1\times {10}^{13}\hspace{0.5em}\mathrm{W}/{\mathrm{cm}}^2$. The spectral characteristics of the HHG from nanoparticles produced in situ are compared with the HHG from monoparticle plasma plumes and with the HHG from preformed nanoparticle-containing plasma plumes. The cutoff harmonic order generated using the in situ silver nanoparticles is at the 21st harmonic order.

Figure 1

Experimental setup for producing harmonics from nanoparticles produced in situ.

Figure 2

AFM images of the silver deposition in the case of (a) weak ($I~{10}^{10}$ W/cm${}^2$) excitation and (b) strong ($I~{10}^{13}$ W/cm${}^2$) excitation of targets. The horizontal and vertical axes show the scan sizes of the two images, whereas the vertical bar at right shows the color coding for different sized nanoparticles.

Figure 3

Comparison of the HHG spectra from (a) silver monoparticles, (b) silver nanoparticles produced in situ, and (c) from coated silver nanoparticles. The intensity of the HHG emission is normalized for better comparison. The curves (b) and (c) are shifted vertically for visual clarity.