Photocurrent induced by nonlinear optical effects has innovated fundamental optic physics in optoelectronic devices, including nonlinear photodetectors, nonlinear optical absorbers, and solar cells. The cooperative interaction between different kinds of nonlinear photocurrents would be a complex yet interesting issue. Herein, we have prepared tellurium (Te) nanotube films to study the transient nonlinear photocurrent utilizing terahertz (THz) emission spectroscopy excited by a femtosecond pulse laser. The THz wave is generated from the interplay between the ultrafast shift current and ultrafast photon drag current, which are ascribed to the photogalvanic effect (PGE) and photon drag effect (PDE), respectively. According to the THz emission spectroscopy excited from opposite incident planes, the contribution ratio of the PDE and PGE is calculated as 1.2:1 for the THz parallel E THz-p component and 1:1 for the perpendicular E THz-s component under the p-polarized excitation. The different ratios between these two components are related to the different nonlinear susceptibility tensor elements. In particular, the contribution of the PDE and PGE can be dynamically modulated by the polarization angle of the incident laser, which further flexibly modulates both E THz-p and E THz-s . As such, the reconstructed THz wave is elliptically polarized with the fixed ellipticity, while the major axis of the ellipse rotates clockwise with different magnitudes. These results highlight the THz emission spectroscopy as an effective tool to clarify the interplay mechanism between different nonlinear photocurrents, which could open a new avenue for ultrafast photovoltaic applications.

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All-optical terahertz (THz) modulators have received tremendous attention due to their significant role in developing future sixth-generation technology and all-optical networks. Herein, the THz modulation performance of the Bi2Te3/Si heterostructure is investigated via THz time-domain spectroscopy under the control of continuous wave lasers at 532 nm and 405 nm. Broadband-sensitive modulation is observed at 532 nm and 405 nm within the experimental frequency range from 0.8 to 2.4 THz. The modulation depth reaches 80% under the 532 nm laser illumination with a maximum power of 250 mW and 96% under 405 nm illumination with a high power of 550 mW. The mechanism of the largely enhanced modulation depth is attributed to the construction of a type-II Bi2Te3/Si heterostructure, which could promote photogenerated electron and hole separation and increase carrier density dramatically. This work proves that a high photon energy laser can also achieve high-efficiency modulation based on the Bi2Te3/Si heterostructure, and the UV-Visible control laser may be more suitable for designing advanced all-optical THz modulators with micro-level sizes.