Ultrafast laser-triggered emission from hafnium carbide tips

TL;DR

This study investigates ultrafast laser-induced electron emission from hafnium carbide tips, revealing two-photon emission at low power and thermally-enhanced field emission at higher powers, with thermal effects modeled and compared across materials.

Contribution

It provides the first detailed analysis of ultrafast laser-triggered emission mechanisms in HfC tips, including thermal modeling and comparison with other materials.

Findings

Two-photon emission observed at low laser power

Thermally-enhanced field emission dominates at higher power

Thermal transient effects are negligible compared to two-photon emission

Abstract

Electron emission from hafnium carbide (HfC) field emission tips induced by a sub-10 fs, 150 MHz repetition rate Ti:sapphire laser is studied. Two-photon emission is observed at low power with a moderate electric bias field applied to the tips. As the bias field and/or laser power is increased, the average current becomes dominated by thermally-enhanced field emission due to laser heating: both the low thermal conductivity of HfC and the laser's high repetition rate can lead to a temperature rise of several hundred Kelvin at the tip apex. The contribution of current from a thermal transient at times shorter than the electron-phonon coupling time is considered in the context of the two-temperature model. Under the conditions of this experiment, the integrated current from the thermal transient is shown to be negligible in comparison with the two-photon emission. A finite element model of the laser heating and thermal conduction supports these conclusions and is also used to compare the nature of thermal effects in HfC, tungsten, and gold tips.