Enhancement of photoelectric emission sensitivity of tungsten by potassium ion implantation

Abstract

Measurements of single-photon photoelectric emission sensitivity of ion implanted polycrystalline tungsten surface by 3×1016 K+ ions/cm2 are reported. They are compared to the data previously obtained for pure tungsten tested under the same conditions. The enhancement of the photoelectric sensitivity up to a factor of 50 was measured as a consequence of the change in the electronic properties of the tungsten surface, induced by the implanted alkali metal ions. Compared with other techniques used to reduce the work function of pure tungsten, the implanted surface exhibits a lower work function than the pure metal, and is capable of supporting high laser intensity for a long time. For these reasons it seems possible to consider the ion-implantation technique as a suitable new method to significantly improve the photoelectric performances of usual metals, under high laser intensity illuminations.

Electron relaxation phenomena on a copper surface via nonlinear ultrashort single-photon photoelectric emission

“…This is the main reason that we perform photoemission and especially single-photon experiments. Very recently, we evaluated the electron-phonon relaxation time of aluminum using the phenomenological theory of [16] and the experimental data related to the single-photon intensity dependent photocurrent measurements [17].…”

Influence of the implanted K-cluster size distribution on the shift of W work function

“…These boundaries are supported by experimental data. [1][2][3][4] The experiments suggest also that dimensions of K clusters in W matrix vary inside a range limited by the two extreme cluster radii observed with electronic spectroscopy, i.e., R min Ϸ5ϫ10 Ϫ10 and R min Ϸ5ϫ10 Ϫ9 m. However, among various cluster distributions versus R c which are more or less probable, we consider below only four typical distributions ͑Fig. 1͒:…”

“…The measurement of a net work function shift at the surface of implanted tungsten photocathodes [1][2][3][4] have proven the efficiency of alkali-atoms implantation in the lowering of the potential barrier at the surface of transition metals. Such a shift of potential barrier ͑up to 2 eV͒ of polycrystalline tungsten implanted by 30-110 keV K ϩ ions, cannot be explained by the assumption of single implanted atoms distributed in full statistical disorder in the tungsten matrix.…”

Ultrashort laser-induced electron photoemission: a method to characterize metallic photocathodes

“…It should be noted that a nonlinear enhancement of the single-photon photoelectron current density is observed when high-intensity, sub-picosecond laser pulses illuminate metallic surfaces. In our recent work [4,8] we have shown that electron relaxation phenomena are strongly connected with the electron photoemission process.…”

“…Such electron sources may find practical applications in accelerators, injectors for free-electron lasers, x-ray sources and TV tubes [1,2]. Most of the existing work on laser photocathodes focuses on metallic surfaces [3][4][5][6][7][8]. Such studies have shown that electron relaxation phenomena play a major role in the long, practically infinite, lifetime of metallic photocathodes and in their high laser damage threshold in the femtosecond regime (∼100 GW cm −2 ).…”