| 摘要 |
The present Fresnel zone plate (20) is comprised of a plate with alternating thin and thick transparent zones. The thin transparent zones (21) are of the same thickness, and the thick transparent zones (22) are of the same thickness. All zones have parallel opposite faces. The thick transparent zones are thicker than the thin transparent zones by a suitable amount to delay incoming destructive waves by an integer of at least zero plus half a wavelength, so that after the waves are passed through the zone plate, waves in all zones are in phase with each other when they reach a focal point (P). Thus, all the zones are transparent constructive zones for passing all incoming radiation to produce twice the amplitude or four times the intensity of a conventional Fresnel zone plate. |
