Visualization of terahertz surface waves propagation on metal foils

Abstract

Exploitation of surface plasmonic devices (SPDs) in the terahertz (THz) band is always beneficial for broadening the application potential of THz technologies. To clarify features of SPDs, a practical characterization means is essential for accurately observing the complex field distribution of a THz surface wave (TSW). Here, a THz digital holographic imaging system is employed to coherently exhibit temporal variations and spectral properties of TSWs activated by a rectangular or semicircular slit structure on metal foils. Advantages of the imaging system are comprehensively elucidated, including the exclusive measurement of TSWs and fall-off of the time consumption. Numerical simulations of experimental procedures further verify the imaging measurement accuracy. It can be anticipated that this imaging system will provide a versatile tool for analyzing the performance and principle of SPDs.

Figure 1. THz digital holographic imaging system.

(a) Optical configuration of the imaging system. (b) Two-dimensional pattern of a TSW excited by the sub-wavelength scale structure of a metal foil. (c) Orientation of the ZnTe crystal. The < 100 > direction of the ZnTe crystal is parallel to the z axis. The angle α between the < 010 > direction of the ZnTe crystal and the x axis is 45 degree.

Figure 2. Imaging the linear TSW generated by a rectangular slit structure.

(a) Schematic of the slit sample. (b–d) Time sequences of the TSW distribution on the exit facet of the slit sample at 0.67 ps, 1.60 ps and 3.60 ps. (e–g) Amplitude, wrapped phase and real part images of the TSW for the 0.44 THz component. (h) Corresponding simulated real part pattern acquired by using the FDTD algorithm.

Figure 3. Frequency-dependent characteristics of the linear TSW.

(a–c) Amplitude profiles of the linear TSW along the line x = 0.0 mm for 0.44 THz, 0.62 THz and 0.91 THz. (d–f) Corresponding wrapped phase plots for different frequencies.

Figure 4. Influence of the orientation of the rectangular slit to the excited TSW.

(a,c) Peak amplitude images of emerging transverse THz components from the rectangular slit aligned perpendicular and parallel to the incident THz polarization. (b,d) Corresponding amplitude images of the transient TSWs at 0.67 ps time delay.

Figure 5. Measurement of the converged TSW excited by a semicircular slit structure.

(a) Schematic of the slit sample. (b–d) Transient patterns of the TSW at selected three times of 1.07 ps, 4.27 ps and 14.13 ps. (e–g), Reconstructed amplitude, wrapped phase and real part distributions of the TSW at 0.44 THz. (h) Corresponding numerical simulation of the real part pattern.