Electron densities, temperatures, and the dielectric function of femtosecond-laser-produced plasmas

The optical properties of dense plasmas in the extreme ultraviolet spectral range are investigated experimentally and theoretically. A method is presented that enables measurement of electron densities in excess of ${10}^{24}\hspace{0.5em}{\mathrm{cm}}^{-3}.$ High-order harmonics are transmitted through a femtosecond-laser-produced plasma probing the optical density at several wavelengths. This technique has the advantage of providing direct access to ultrahigh electron densities, and achieves a precision of about 20% at zero time delay. The dielectric function of a dense carbon plasma was calculated including effects of higher density and the contribution of bound electrons.