2005 Volume 71 Issue 8 Pages 1031-1035
The technological innovation using the extreme ultraviolet wavelength (EUV) with high brightness of synchrotron radiation is actively advanced. In order to effectively utilize such light, it is important to develop the technology that produces and evaluates the optical elements with very high surface accuracy. The point diffraction interferometer is an interferometer that has inherent high accuracy using a circular aperture with a radius comparable to the wavelength of light. We are constructing a point diffraction interferometer as a profile measurement sensor, which can be also utilized for alignment of the EUV optical system. The optical system is consisted of single-mode optical fiber and fringe scanning using the laser source of visible light. But, the extra interference and diffraction waves are included for original interference fringe. In this report, the effect of the temporal coherence length of light source on the measurement accuracy was investigated by experiments and simulation analyses. As the result, when adjusting optical path difference of the object and reference waves the optimal, it was shown clearly that high accuracy measurement is possible. Furthermore, if a light source of the shorter coherence length is used, the alignment will become easy and its accuracy will also improve more.
