Science and technology trends: circularly polarized laser controls graphene to generate reverse photocurrent

The State Key Laboratory of Intensive Field Laser Physics, Shanghai Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, has made progress in the control of single-layer graphene by circularly polarized laser to generate reverse photocurrent. Graphene has the properties of weak shielding, high damage threshold and ultra-fast optical response. It is a new material with application prospects to realize the control of electronic motion by femtosecond ultra-fast laser.

By solving the time-dependent Schrodinger equation and the semiconductor Bloch equation numerically, researchers studied the photocurrent generated by circularly polarized few-period laser driving single-layer graphene. The results show that for the two period circularly polarized laser, the optical current direction reversal can be achieved under a certain laser peak field strength by selecting the appropriate laser wavelength. The occurrence of direction reversal comes from the interference between optical periods, which can be verified by artificially shortening the pulse width to a single period.

The inversion threshold is proportional to the negative square of the laser wavelength in a wide range, and its slope is related to the ratio of the mass kinetic energy of the electron to the photon energy. This study reflects the nature of the motion of the electron in the two-dimensional inverted space, and has certain guiding significance for realizing the application of ultrafast optoelectronic integration.

Figure 1: Photocurrent changes with laser peak field intensity, incident wavelength 4 μ m. (a) pulse width 26fs, (b) pulse width 13fs.

Source: Shanghai Institute of Optics and Precision Machinery, Chinese Academy of Sciences