Fig. 1. Diagram of chiral THz generation and modulation. (a) fs laser along the z axis is vertically incident on the patterned emitter surface with the external magnetic field along the y axis. Elliptically or circularly polarized THz waves can be obtained when selecting an appropriate device and rotating it in the x−y plane by φ. The inset illustrates that it will shunt along the edges of the pattern once the charge current appears. With electrons gathering at the edge, the built-in electric fields are built to lead the amplitude and phase difference between the orthogonal current direction. (b) The main structure is Pt(2 nm)/CoFeB(2 nm)/W(5 nm), which can radiate THz waves relying on ISHE. (c) The schematic diagram is the built-in electric field distributing in the stripes array when φ is 0, where the red balls represent positive charges and the blue balls are electrons at the edge of patterns. (d)–(f) The control effect of devices in this experiment on THz polarization: we can achieve linear polarization, right- or left-handed elliptically or circularly polarized THz waves. The color bar represents the distribution range of the signal in the time domain.

Fig. 2. Analysis of the effect of the built-in electric field on THz measurement. (a)–(c) Investigation of THz emission efficiency, frequency domain, and pump dependence in different samples when φ is 0 deg. (d)–(f) Investigation of THz emission efficiency, frequency domain, and pump dependence in different samples when φ is 90 deg.

Fig. 3. THz chirality modulation performance based on the built-in electric field. (a) Schematic diagram of forces on electrons accumulating at edges and current distribution in samples when rotating to φ (0deg<φ<90deg). (b) Extracted backflow ja and jb from D1, D4, and D7 at 20 and 60 deg. (c), (d) Comparison of broadband amplitude and phase with and without ji. (e) Polarization modulation effects (the phase difference distribution in the full frequency domain) of D4 to D7 at 20, 45, and 60 deg, respectively. (f) Phase differences in the time domain of D1 to D7 at 20, 45, and 60 deg. (g) Ellipticity in the time domain of D1 to D7 at 20, 45, and 60 deg. (h) THz amplitude peaks with the increase of l/w at 20 deg. (i) Lissajous curves of all devices at 20 deg.

Fig. 4. Left- and right-handed THz wave modulation performance based on the built-in electric field and the azimuth. (a) Manipulation of the THz chirality by rotating azimuth angles of devices. (b)–(d) 3D time-domain waveforms describing the polarization states of D1, D4, and D7 at 20 and 160 deg. (e) Fourier transformed spectra of D4 and their corresponding phase in the x and y directions. (f) Fourier transformed spectra of D7 and their corresponding phase in the x and y directions.

Fig. 5. Broadband manipulation for THz polarization states by changing azimuth angles. (a) Schematic diagram of rotating sample with the fixed magnets. (b) THz time-domain waveforms in the x and y directions. (c) Distributions of the phase difference (frequency domain) of D7 for all angles in the full-frequency band. (d) jy/jx is used to visually illustrate the modulation effect of THz amplitude in different aspect ratios during azimuth rotation. (e) Calculation and measurement of the phase difference (time domain) in D7 at different azimuth angles. (f) Lissajous curves describing the polarization states of D7 during azimuth rotation. (g) Different ellipticity distributions in broadband THz frequency bandwidth at different azimuth angles. (h) Poincaré sphere in the range of ∼0.74 to 1.66 THz at seven different azimuth angles.

Fig. 6. Various chiral THz beam generation over broadband frequency domain. (a) The 3D polarization spectrum of a polarized THz wave. (b)–(d) Polarization states of THz waves under different azimuth angles at 0.7, 1.1, and 1.5 THz.