Emission of charged particles from laser-induced germanium ecton, vacuum spark and vacuum arc

TL;DR

This study investigates the temporal evolution and mechanisms of charged particle emission from laser-induced germanium micro-explosions, revealing distinct behaviors depending on breakdown conditions and demonstrating efficient ion cluster emission.

Contribution

It provides detailed insights into the emission dynamics and mechanisms during laser-induced germanium explosions, including breakdown effects and plasma oscillations, which were not previously characterized.

Findings

Electron emission occurs with a 30° opening angle.

Electron bunches of several nanocoulombs are emitted without breakdown.

Breakdown causes a change in arc behavior and indicates different evaporation mechanisms.

Abstract

The highly resolved temporal evolution of laser-induced micro-explosions on a germanium surface is studied in a triode configuration for various gate charge levels and cathode currents. Electron emission from individual spots is directly imaged with a luminescence screen, showing that the opening angle of the source is about 30$^\circ$. Electron bunches of several nanocoulombs per pulse in a time interval of about 150 ns are directly extracted to the anode without vacuum breakdown in the cathodic gap. When breakdown occurs, a remarkable change in the arc behavior of a threshold gap potential of around 1 kV is observed, which hints at two different evaporation mechanisms that depend on the cathodic fall of an individual spot. Therefore, for voltages well above the threshold, a fast gate discharge is observed within the first 100-200 ns, followed by fundamental plasma oscillations and an electron emission of several $\mu$C per pulse from the plasma boundary. Additionally, highly efficient emission of germanium ion clusters occurs, evidencing a stable two-fold electron multiplication in the plasma, with a charge of several $\mu$C per pulse below the threshold.