Fig. 8: The measured THz Bessel beams generated for different ΔLx: -6 μm (a1-d1) and -56 μm (a2-d2).

a1, a2 THz transverse spatial intensity distributions, b1, b2 THz 1D transverse intensity distributions along horizontal direction, c1, c2 1D axial THz intensity, d1, d2 the peak intensity of THz rings in (c1, c2) with different propagation distances.