Injection and All‐Optical Coherent Control of Ultrafast Photocurrent in 2D SnSe₂ Film Excited by Dual‐Color Laser Fields

Abstract The 2D material tin diselenide (SnSe 2 ) exhibits remarkable potential within the optoelectronics domain, attributed to its distinctive electronic structure and optical characteristics. Under dual‐color laser field excitation at 800 and 400 nm, the injection and coherent control of ultrafast photocurrent in SnSe 2 are complex owning to its direct and indirect bandgap energies being below the fundamental photon energy. The photocurrent injection in SnSe 2 is studied via measuring its emitted terahertz wave. There are two quantum interference channels: one between single‐ and two‐photon absorptions, and the other between stimulated electronic Raman scattering and single‐photon absorption. Both induce asymmetric carrier distribution in momentum space, leading to coherent photocurrent injection. Moreover, under the collinearly polarized dual‐color laser field excitation, the amplitude and polarity of THz radiation (photocurrent) can be coherently controlled by altering the relative phase of the laser fields. When the fields are co‐circularly polarized, the polarization direction of emitted THz radiation can be coherently controlled by relative phase, and its rotation direction depends on the helicity of the circularly polarized fields. This work improves the understanding of electron transitions and ultrafast photocurrent injection in narrow‐bandgap SnSe 2 and offers an all‐optical method for the coherent control of ultrafast photocurrent.