Cross-sectional view of the spatial profiles of the bias field E b for (a) large-aperture (∼1 cm) stripline antenna and (b) small-gap (∼10 μm) dipole antenna. The negative z values corresponding to positions inside the photoconductor. The nominal strength of E b is assumed to be about 2.0 kV cm−1. The arrows indicate the E b vectors, the (+) and (–) symbols denote positive and negative terminals located on the transmission line structures for the two types of antennas, respectively.
Time evolutions of (a) a pump pulse Ip , (b) carrier density n, and effective absorption coefficient α at four different times: t = 0.5 ps (brown), 1.1 ps (green), 1.63 ps (blue), and 1.8 ps (red). The horizontal z-axis indicates positions along the direction of propagation of the pump pulse. The solid purple line indicates the interface of air (white region) and antenna (yellow region) at z = 0.5 mm. As shown in Fig. 1 , the magnitude of the bias field Eb is significant only between the solid and dashed purple lines (∼7 μm) for small-gap antennas.
Radiated THz field from a large-aperture antenna. The vertical line at z = 0.5 mm indicates the interface of air and antenna. (a) Time evolution of the field E x at four different times t = 0.5, 1.1, 1.63, and 1.8 ps. (b) temporal waveforms of Near-field E x (blue line) and far-field E THz (red line) fields.
THz radiation generated from a small-gap antenna. (a) Time evolution of the field E x at four different times t = 0.5, 1.1, 1.63, and 1.8 ps. The yellow region denotes the antenna, the region of significant E b is located between the solid and dashed purple lines. (b) Temporal waveforms of the Near-field E x (blue line) and far-field E THz (red line). In the simulation, the depth of non-zero bias field, E b, Δz = 7 μm, the spatial extent of the pump pulse wp = 40 μm, the propagation speed of pump pulse in the photoconductor v p = 8.3 × 107 m s−1, thus τ b ≈ 0.08 ps and τ w ≈ 0.48 ps.
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