Making parabolic mirrors by electron-beam gun evaporation method with ion-assisted deposition

A spherical surface was modi®ed to form a parabolic surface by the evaporation of Al2O3 ®lms and an ion-assisted deposition process using a designed mask. The stress of the evaporated ®lms was measured by a phase shifting Twyman± Green interferometer. Ion beam bombardment was proven to reduce the stress of Al2O3 ®lms. The optimum ion beam voltage and ion beam current density for reducing the ®lm stress were 300 Vand 16 mA/cm2 for Al2O3 ®lms.#2001 Elsevier Science B.V. All rights reserved