Investigation on diffraction characteristics of continuous terahertz beam limited by hard-edge apertures

Hard-edge apertures are common devices in optical systems. The light beam would be diffracted while transmitting through an aperture. The diffraction characteristics of terahertz (THz) beam passing through two hard-edge apertures have been simulated based on the Fresnel diffraction integral function, and an approximate parallel beam has been obtained. The effect on the diffraction spot has been compared and analyzed by changing the aperture diameter and distance between the two apertures and the diffraction plane. Then the experimental results were presented, which basically accorded with the numerical results. It can be inferred that the diameter of THz beam diminishes and the divergence angle can be neglected after the restriction of two apertures. The method is preferably available in some experiments which require small beam diameter and divergence angle.