Precise and ultrafast control over photo-induced charge currents across nanoscale interfaces could lead to important applications in energy harvesting, ultrafast electronics, and coherent terahertz sources. Recent studies have shown that several relativistic mechanisms, including inverse spin-Hall effect, inverse Rashba–Edelstein effect, and inverse spin-orbit-torque effect, can convert longitudinally injected spin-polarized currents from magnetic materials to transverse charge currents, thereby harnessing these currents for terahertz generation. However, these mechanisms typically require external magnetic fields and exhibit limitations in terms of spin-polarization rates and efficiencies of relativistic spin-to-charge conversion. We present a nonrelativistic and nonmagnetic mechanism that directly utilizes the photoexcited high-density charge currents across the interface. We demonstrate that the electrical anisotropy of conductive oxides RuO2 and IrO2 can effectively deflect injected charge currents to the transverse direction, resulting in efficient and broadband terahertz radiation. Importantly, this mechanism has the potential to offer much higher conversion efficiency compared to previous methods, as conductive materials with large electrical anisotropy are readily available, whereas further increasing the spin-Hall angle of heavy-metal materials would be challenging. Our findings offer exciting possibilities for directly utilizing these photoexcited high-density currents across metallic interfaces for ultrafast electronics and terahertz spectroscopy.
We experimentally demonstrate that temporally confined spatial solitons can be realized by space-time coupled propagation of strong femtosecond pulses in a nonlinear optical resonator, consisting of periodic layered Kerr media (PLKM). A universal relationship between the characteristic beam size and the critical nonlinear phase of the solitary modes is revealed, defining different regions of soliton stability. Taking advantage of the unique characters of these solitary modes, we demonstrate supercontinuum generation and pulse compression of initially 260 μJ, 170 fs pulses down to 22 fs in a single-stage PLKM resonator with an efficiency >90%.
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