Patent ID: 7050175

Claim:
A method for calibrating an interferometer optics for measuring optical surfaces, said method comprising: arranging a first substrate having a first surface and a second surface opposite said first surface in a beam path of a first incident beam provided by said interferometer optics with said first surface facing towards said first incident beam, and interferometrically taking a first measurement of first wave fronts generated by reflecting said first incident beam from said second surface of said first substrate; arranging said first substrate in said beam path of said first incident beam with said second surface facing towards said first incident beam, and interferometrically taking a second measurement of second wave fronts generated by reflecting said first incident beam from said second surface of said first substrate; arranging a third surface of a second substrate in a beam path of a second incident beam, and interferometrically taking a third measurement of third wave fronts generated by reflecting said second incident beam from said third surface of said second substrate, while said first substrate is not arranged in said beam path of said second incident beam; arranging said third surface of said second substrate and said first substrate in said beam path of said second incident beam, and interferometrically taking a fourth measurement of fourth wave fronts generated by reflecting said second incident beam from said third surface and through said first substrate; and determining optical properties of said interferometer optics in dependence of said first, second, third and fourth measurements.