Fig. 1. Schematic diagrams of single-shot optical pump-terahertz detection system. (a) A schematic illustration of the setup (KDP: KH₂PO₄; DM: dichroic mirror; BS: beam splitter; LN: lithium niobate wafer; OAP: off-axis parabolic mirror; MM: metal mirror; TD1, TD2: terahertz detection delay line and pump delay line; RE: reflective echelon; W1, W2: wire grid polarizers; ITO: indium tin oxide thin film; ZnTe: zinc telluride detector crystal; QWP: 1/4 wave plate); (b)(c) reflection and transmission imaging results of free-standing gold foils with the diameter of 2 mm and the thickness of 30 nm, respectively; (d) spatial arrangement of optical pump and terahertz probe; (e) schematic diagram of the surface structure of the reflective echelon

Fig. 2. Comparison of terahertz waveform between single-shot detection and traditional multi-shot scanning detection. (a) Single-shot signal with THz on; (b) single-shot background signal with THz off; (c) single-shot terahertz modulation signal,ΔI/I0=ITHzon-ITHzoff/ITHzoff; (d) comparison between the single-shot waveform (solid line, ΔI/I0) obtained by vertical integration of Fig. 2 (c) and the multi-shot waveform obtained by traditional multi-shot scanning (dot dash line)

Fig. 3. Terahertz energy characterization. (a) The dependence of laser pulse duration on the grating position, and the variation of terahertz pulse energy with grating position for different pump laser energies (from top to bottom: 1, 0.8, 0.7, 0.6, and 0.4 J); (b) at a pulse duration of 126 fs, the terahertz energy fluence and conversion efficiency as a function of pump laser intensity

Fig. 4. Transmitted terahertz signal of the free-standing gold foil and the hole at the pump delay of 3 ps. (a)(b) Changes in probe optical intensity (ΔI=ITHzon-ITHzoff) with and without THz radiation for the gold foil and the hole, respectively; (c)(d) THz time-domain waveforms obtained from ΔI/I0 for the gold foil and the hole, respectively; (e)(f) the corresponding frequency spectra of Figs.4(c) and (d)

Fig. 5. Variations in the electrical conductivity σ0 and THz transmittance of the free-standing gold foil as a function of pump-probe delay (negative delay indicates that the terahertz wave arrives at the free-standing gold foil before the pump laser), where the solid line represents the time-resolved electrical conductivity at different pump-probe delay obtained from a double exponential function fit and the DC electrical conductivity of bulk pure gold at room temperature (300 K) is shown with five-pointed star symbols^[49], σ_{dc bulk}=4.403×10⁷ S/m