Optical surface of a high-precision metal mirror with very low roughness and shape defect

A manufacturing method comprising the following steps:

• determining a reference shape defect and a reference surface roughness of an optical surface of an optical part, wherein the optical part comprises a substrate and a coating, the coating being applied onto a surface of the substrate and being configured to form the optical surface of the optical part, the substrate being made of a first aluminium alloy and the coating being made of a second aluminium alloy having lesser porosity than a porosity of the first aluminium alloy;
• determining an initial shape defect and initial surface roughness of the coating of the optical part;
• using the initial surface roughness, to determine polishing parameters required to obtain the determined reference surface roughness;
• using the polishing parameters to machine the coating and obtain a machined coating having a machined shape defect;
• and
• using the determined polishing parameters to polish the machined coating by smoothening in order to modify the surface roughness and machined shape defect of the machined coating and obtain modified surface roughness and modified shape defect that correspond to the determined reference roughness and reference shape defect.