External-Magnetic-Field-Free Spintronic Terahertz Strong-Field Emitter

Intense terahertz (THz) radiation in free space has immense potential for regulating material state, accelerating electrons, producing biological effects, and so on. However, the high cost and challenges involved in constructing strong-field THz sources have limited their developments, making it difficult for the potential applications of strong-field THz radiation to be widely adopted. Spintronic THz emitters (STEs) with numerous merits such as high efficiency, ultrabroadband, ease of integration, and low cost have become ubiquitous, but the majority of these emitters require stable operation in the presence of external magnets, limiting their applications, particularly in generating strong fields that necessitate large-sized samples. Here, we demonstrate the feasibility of generating strong-field THz radiation in 4-inch antiferromagnetic material–ferromagnetic metal (IrMn₃ [2 nm]/Co₂₀Fe₆₀B₂₀ [2 nm]/W [2 nm]) without external magnetic field driving. Under the excitation of a Ti:sapphire femtosecond laser amplifier with a 35-fs pulse duration and a 1-kHz repetition rate, we obtain strong-field THz radiation from our STEs with a pulse duration of ~110 fs, and a spectrum covering up to ~10 THz. Further scaling up the pump laser energy up to 55 mJ with a pulse duration of ~20 fs and a repetition rate of 100 Hz provided by the Synergetic Extreme Condition User Facility, the radiated THz electric field strength from the external-magnetic-free 4-inch STEs can exceed 242 kV/cm with a pulse duration of ~230 fs, a spectrum covering up to ~14 THz, and a single pulse energy of 8.6 nJ measured by a calibrated pyroelectric detector. Our demonstrated external-magnetic-field-free high-field STEs have some unique applications such as producing sub-cycle ultrashort strong THz fields in huge size emitters under the excitation of high-energy light sources, accelerating the development of THz science and applications.