TWYMAN-GREEN INTERFEROMETER FOR TESTING MICROSPHERES

Testing of spherical surfaces using the Twyman-Green interferometer wi th a laser source suffers from the presence of spurious interference f ringes and dust diffraction. By reducing the spatial coherence while m aintaining the temporal coherence a tremendous improvement of the frin ge quality can be obtained. To conserve sufficient contrast, the refer ence mirror must be positioned to suitable locations relative to the t est arm of the interferometer. These conditions are described and exam ples are presented.