Laser absorption in short-lived metal and nanoplasmas

We have studied the absorption of 100 fs, 806 nm laser pulses in both bulk and nanoparticulate forms of copper as a function of the electric field intensity as well as polarization. In particular, we have investigated the changes in absorption over a wide range of intensity (over four orders of magnitude) which enables us to study the transition of a metal to plasma. We have found that, even in its nanoparticulate form, the onset of plasma formation occurs in copper when the incident light field intensity is about 10 W. The values of the dielectric permittivities, calculated using the Drude theory, deviate from the room temperature values beyond the onset of plasma formation.