  THz pulses are generated from femtosecond pulse-excited
ferromagnetic/nonmagnetic spintronic heterostructures via inverse spin Hall
effect. The contribution from ultrafast demagnetization/remagnetization is
extremely weak, in the comparison. The highest possible THz signal strength
from spintronic THz emitters is limited by the optical damage threshold of the
corresponding heterostructures. The THz generation efficiency does not saturate
with the excitation fluence even up till the damage threshold. Bilayer (Fe,
CoFeB)/(Pt, Ta) based 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 on a
quartz substrate, having alpha-phase Ta as the nonmagnetic layer, show the
highest damage threshold as compared to those with Pt, irrespective of their
generation efficiency. The damage threshold of the Fe/Ta heterostructure on
quartz substrate is ~85 GW/cm2.
