Optical and photoelectric properties of alkali metals

The paper gives, in the form of tables and graphs, the optical constants and photoelectric emisssion for the four alkali metals Cs, Rb, K, and Na in the spectral range 250-630 nm inside which the volume-plasmon wavelengths ${\lambda }_p$ and the surface-plasmon wavelength ${\lambda }_s$ are situated. The metals are prepared in the form of optically thick layers condensed in ultrahigh vacuum (${10}^{-11\mathrm{}}$ torr) on targets cooled at 77 °K. When maintained at 77 °K, the layers show a spectral selectivity independent of the state of polarization of the exciting monochromatic radiation. Upon reheating at 195 °K or higher, a very pronounced vectorial selectivity appears, accompanied by diminution of the photoemission. Values given in the tables and graphs are reproducible within a fair approximation, stated in each case. From the "optical" conductivity curves $\sigma =f\left(\hslash \omega \right)$, it is not possible to identify an absorption process due to interband transitions (Wilson-Butcher theory). The plot of the real part of the dielectric constant against the square of the exciting radiation wavelength ${\epsilon }_1=f\left({\lambda }^2\right)$ is perfectly linear for all reheated layers, thus allowing use of the Cohen and the Fowler formulas in the calculation of $\sigma$, ${\lambda }_p$, the "optical" mass, the polarizability, and the work function for several temperatures. The normal reflectivity curves for the reheated layers show a point of inflection for $\lambda ={\lambda }_P$. For the same layers, the quantum efficiency of the photoemission shows a minimum for $\lambda ={\lambda }_p$, particularly well marked for the lighter metals. Finally, the work-function values at 0 °K extrapolated from our experimental results by the Fowler process, are shown to have two values $W_{\parallel }$ and $W_{\perp }$ whenever the layer investigated exhibits vectorial selectivity; the difference $W_{\parallel }-W_{\perp }$ is only a few hundredths of an electron volt but is quite reproducible.