Tunable ultrafast thermionic emission from femtosecond-laser hot spot on a metal surface: role of laser polarization and angle of incidence

TL;DR

This study explores how laser polarization and angle of incidence affect ultrafast thermionic emission from gold surfaces, revealing polarization-dependent behaviors and their implications for designing ultrafast electron emitters.

Contribution

It introduces an advanced 3D two-temperature model incorporating dynamic reflectivity and space charge effects to analyze thermionic emission under various laser conditions.

Findings

Peak electron temperature increases with angle of incidence for P polarization.

Thermionic emission duration depends strongly on angle and polarization.

Emission duration correlates with electron-lattice thermalization time.

Abstract

Ultrafast laser induced thermionic emission from metal surfaces has several applications. Here, we investigate the role of laser polarization and angle of incidence on the ultrafast thermionic emission process from laser driven gold coated glass surface. The spatio-temporal evolution of electron and lattice temperatures are obtained using an improved three-dimensional (3D) two-temperature model (TTM) which takes into account the 3D laser pulse profile focused obliquely onto the surface. The associated thermionic emission features are described through modified Richardson-Dushman equation, including dynamic space charge effects and are included self-consistently in our numerical approach. We show that temperature dependent reflectivity influences laser energy absorption. The resulting peak electron temperature on the metal surface monotonically increases with angle of incidence for P polarization, while for S polarization it shows opposite trend. We observe that thermionic emission duration shows strong dependence on angle of incidence and contrasting polarization dependent behaviour. The duration of thermionic current shows strong correlation to the intrinsic electron-lattice thermalization time, in a fluence regime well below the damage threshold of gold. The observations and insights have important consequences in designing ultrafast thermionic emitters based on a metal based architecture.