Fig. 1. (a) Setup 1: Experimental setup for coherent photocurrent control by the THz time-domain emission spectroscopy under 400 + 800 nm excitation. BS: beam splitter. M: mirror. OW: optical wedge. OAP: off-axis parabolic mirror. QWP: quarter-wave plate. WP: Wollaston prism. (b) Schematic diagram of the spatial overlap of the 800 nm (ω) and 400 nm (2ω) pulses. (c) Setup 2: (I) Schematic diagram of only 800 nm laser excitation without any additional optical components. (II) Inserting the α-BBO crystal based on (I). (III) Inserting the OW based on (II). (d) Setup 3: (i) Schematic diagram of only 400 nm laser excitation. (ii) Inserting the α-BBO crystal based on (i). (iii) Inserting the OW based on (ii).

Fig. 2. (a) Normalized THz time-domain signals of GaAs excited by both ω (800 nm, red) and 2ω (400 nm, blue) pulses. (b) Normalized THz time-domain signals of GaAs excited by both ω and 2ω pulses after adding the α-BBO crystal. (c) Normalized THz time-domain signals of GaAs excited by both ω and 2ω pulses after passing through both OW and α-BBO crystal. (d) Dispersion curves of OW (purple line) and α-BBO crystal (red dashed line: ordinary wave; blue dashed line: extraordinary wave). (e) Theoretical calculation of the time delay between ω and 2ω pulses as a function of the α-BBO crystal thickness. (f) Theoretical calculation of the time delay between ω and 2ω pulses as a function of the OW thickness.

Fig. 3. (a) Contour mapping of the THz time-domain waveforms with the relative phase between ω and 2ω pulses. The black lines represent the THz time-domain waveforms when Δφ = −π/2 (bottom line) and Δφ = π/2 (upper line). (b) The relative phase dependences of the THz peak-to-valley amplitude values after removing the background effect. Inset: the relative phase difference by moving the optical wedge.