Fig. 1. THz time-domain spectroscopy system driven by direct diode pumped Ti∶sapphire laser oscillator and experimental results of nano-metasurface. (a) Internal lightpath of Ti∶sapphire laser oscillator and lightpath diagram of THz time-domain spectroscopy system; (b)(c) reference signal generated and detected by the photoconductive antenna as well as THz waveforms from metasurface under TE and TM conditions and corresponding spectra; (d) relative transmission spectra under different incident conditions

Fig. 2. Spintronic THz emission experiment driven by femtosecond laser without external magnetic field. (a) Lightpath diagram of THz emission spectroscopy system; (b) sketch of THz radiation from IrMn₃|Co₂₀Fe₆₀B₂₀|W pumped by femtosecond laser and the sample structure diagram; (c)(d) THz time-domain signal and corresponding spectrum of IrMn₃|Co₂₀Fe₆₀B₂₀|W

Fig. 3. Ultrabroadband THz emission signal generated from spintronic THz emitters. (a)(b) THz radiation wave from a spintronic THz emitter pumped by 30 fs femtosecond laser and its spectrum exceeding 5 THz; (c)(d) THz radiation wave from a spintronic THz emitter pumped by 20 fs femtosecond laser and its spectrum exceeding 10 THz

Fig. 4. Dependence of THz emission signals on sample azimuth angle. (a) Waveforms of THz emission signals at different azimuth angles, waveforms are shifted by time to express clearly; (b) dependence curve between THz peak-to-peak value and sample azimuth angle

Fig. 5. Effect of flipping sample on THz emission signals. (a)(b) Schematics of left-right flipping and up-down flipping; (c) THz time-domain signals of IrMn₃|Co₂₀Fe₆₀B₂₀|W; (d) THz emission signals after left-right flipping and up-down flipping

Fig. 6. Effect of applying in-plane magnetic field on THz radiation. (a)(c) Schematic of applying in-plane magnetic field and THz emission signals; (b)(d) principle and waveforms of THz emission signal variation induced by external opposite magnetic fields

Fig. 7. Relationship between THz emission signals and pump power. (a) THz time-domain waveforms obtained from high to low pump power; (b) dependence of THz peak-to-peak value on pump power

Fig. 8. Defocused enhanced spintronic THz emission phenomenon based on the Ti∶sapphire oscillator pumped by semiconductor. (a) THz emission signals obtained before and after the focusing lens focus, with the left side of the zero point being before the focus and the right side being after the focus; (b) variation of THz peak-to-peak value with defocus position