Efficient terahertz generation using Fe/Pt spintronic emitters pumped at different wavelengths

Abstract

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 effecta 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 μm MgO substrate is just as effective as a THz radiation source when excited either at λ = 800 nm or at λ = 1550 nm by ultrafast laser pulses from a fs fiber laser (pulse width ~100 fs, repetition rate ~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.

Ultrafast Demagnetization of Iron Induced by Optical versus Terahertz Pulses

“…Second, because ultrafast spin transport is driven by the same force as UDM [6,7], it should exhibit the same dynamics, independent of the photon energy of the pump pulse. Such behavior was indeed reported recently [10,11]. Setup details.…”

“…In terms of applications, UDM is an important process in all-optical magnetization switching [2]. It is driven by the same force as ultrafast spin transport [6,7] and, thus, of relevance for applications such as generation of spin torque [8] and terahertz electromagnetic pulses [9][10][11].…”

THz spintronic emitters: a review on achievements and future challenges

“…From both experiments, it seems that the crucial factor is the amount of energy that is deposited by the pump pulse in the electronic system and not the details of the involved optical transitions. By further probing the THz emission of Fe/Pt bilayers at λ = 400 nm [40], the spintronic THz emission efficiency of an optimized spintronic emitter was equal strong as with probing at 800 and 1550 nm. So it still remains independent of the optical pump wavelength.…”

“…So it still remains independent of the optical pump wavelength. In addition, the efficiency is highly tunable with optical pump power [40]. The reason behind the observed effect is a consequence of the fact that the out of equilibrium transport is done not only by the electrons directly excited by the laser, but also by all the electrons that are excited at intermediate energies due to the scattering of the first-generation electrons.…”

Biomedical optics applications of advanced lasers and nonlinear optics

“…By operating at 1550 nm, the system can be pumped using a cheaper and more compact fiber laser system. 51 Increasing the maximum power, while reducing the cost, complexity, and size of THz systems, is essential for future applications. Despite a relatively high cost and existing limitations, THz spectroscopy has already been explored in biomedical spectroscopy and imaging.…”