Plasma density determination by transmission of laser-generated surface harmonics

A diagnostic is proposed for determining the density of laser-generated plasmas. The scheme exploits surface harmonics generated by short, intense laser pulses reflected from an overdense plasma layer. At sufficiently high intensities (I${\lambda }^2$>${10}^{18}$ W ${\mathrm{cm}}^{\mathrm{-}2}$), the reflected spectrum contains harmonics well above the plasma frequency, corresponding to the maximum plasma density. The transmitted spectrum, on the other hand, exhibits a low-frequency cutoff for ω<${\mathrm{\omega }}_{\mathrm{p}}$, offering a simple means of deducing the plasma density.