An optical element has been invented to generate a zero-order quasi-Bessel beam with a certain distance to the element, which does not exist in the zero-order quasi-Bessel beam by using a traditional axicon. The cross section of designed element is an isosceles triangle whose equal sides are circumscribed by two semi-ellipses. Using a well-developed three-dimensional (3D)-printing technique, we have fabricated a series of elements working at terahertz (THz) frequency. Both simulated and experimental results clearly show that there is a certain distance between the generated quasi-Bessel beam and this element. A physical analysis based on geometric optics theory is performed to explain the obtained results. Because it is a refractive transmitted optical element, we propose that it can be also realized at another frequency band if the relevant processing techniques are available.
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