  Recent studies in spintronics have highlighted ultrathin magnetic metallic
multilayers as a novel and very promising class of broadband terahertz
radiation sources. Such spintronic multilayers consist of ferromagnetic (FM)
and non-magnetic (NM) thin films. When triggered by ultrafast laser pulses,
they generate pulsed THz radiation due to the inverse spin-Hall effect, a
mechanism that converts optically driven spin currents from the magnetized FM
layer into transient transverse charge currents in the NM layer, resulting in
THz emission. As THz emitters, FM/NM multilayers have been intensively
investigated so far only at 800-nm excitation wavelength using femtosecond
Ti:sapphire lasers. In this work, we demonstrate that an optimized spintronic
bilayer structure of 2-nm Fe and 3-nm Pt grown on 500 {\mu}m MgO substrate is
just as effective as a THz radiation source when excited either at {\lambda} =
800 nm or at {\lambda} = 1550 nm by ultrafast laser pulses from a fs fiber
laser (pulse width close to 100 fs, repetition rate around 100 MHz). Even with
low incident power levels, the Fe/Pt spintronic emitter exhibits efficient
generation of THz radiation at both excitation wavelengths. The efficient THz
emitter operation at 1550 nm facilitates the integration of such spintronic
emitters in THz systems driven by relatively low cost and compact fs fiber
lasers without the need for frequency conversion.
