Optical damage limit of efficient spintronic THz emitters

Sandeep Kumar,Anand Nivedan,Arvind Singh,Yogesh Kumar,Purnima Malhotra,Marc Tondusson,Eric Freysz,Sunil Kumar

doi:10.1016/j.isci.2021.103152

Abstract

SummaryTHz pulses are generated from femtosecond pulse-excited ferromagnetic/nonmagnetic spintronic heterostructures via inverse spin Hall effect. The highest possible THz signal strength from spintronic THz emitters is limited by the optical damage threshold of the corresponding heterostructures at the excitation wavelength. For the thickness-optimized spintronic heterostructure, the THz generation efficiency does not saturate with the excitation fluence even up till the damage threshold. Bilayer (Fe, CoFeB)/(Pt, Ta)-based ferromagnetic/nonmagnetic (FM/NM) spintronic heterostructures have been studied for an optimized performance for THz generation when pumped by sub-50 fs amplified laser pulses at 800 nm. Among them, CoFeB/Pt is the best combination for an efficient THz source. The optimized FM/NM spintronic heterostructure having α-phase Ta as the nonmagnetic layer shows the highest damage threshold as compared to those with Pt, irrespective of their generation efficiency. The damage threshold of the Fe/Ta heterostructure on a quartz substrate is ∼85 GW/cm2.

Highlights

In conclusion, optical damage threshold of various spintronic heterostructures as efficient THz emitters has been evaluated in this paper
The inverse spin-Hall effect is the main origin for high power THz generation from the bi- and tri-layer FM/NM-type spintronic THz emitters
Detailed experiments were performed to obtain the optimized thicknesses of the individual FM and NM layers in their bilayer combinations, on which further experiments were conducted for the determination of optical damage threshold

Summary

Introduction

When ferromagnetic/nonmagnetic (FM/NM) metallic thin film heterostructures are irradiated with optical femtosecond laser pulses, emission of THz pulses takes place (Li et al, 2019; Wu et al, 2017; Seifert et al, 2016, 2017a, 2017b; Yang et al, 2016; Kampfrath et al, 2013a) Such emitters are unique in the sense that they combine the excitements from the three most active research fields, currently, the ultrafast lasers, spintronics, and THz radiation. The bandwidth of the THz radiation generated from these sources is limited by the duration of the excitation pulse only (Seifert et al, 2016)

Methods

Results

Conclusion