Fabrication of a three-dimensional optical vortices phase mask for astronomy by means of electron-beam lithography

In this work, a novel three-dimensional (3D) fabrication process was used to create a series of particular phase masks for astronomical applications. These phase masks, also known as spiral phase plates (SPP), find their application in astronomy for optical vortex coronagraphy in the search of extra solar planets. The 3D profile was directly written on 2.7 mm thick polymethylmethacrylate (PMMA) slide by electron beam lithography (EBL). The effect of electron scattering on topography profile was investigated and the relationship among spatial distribution of electron beam irradiation, spot size and dosage level of irradiation were experimentally characterized. The quality of the fabricated profiles was evaluated using atomic force microscopy (AFM) technique. SPPs were then optically tested by injecting a Gaussian beam and an airy diffraction pattern obtained from a laser source comparing the optical vortices so far obtained with those drawn with numerical simulations. © 2008 Elsevier B.V. All rights reserved.