P. Hegeman et al., Experimental study of a shearing interferometer concept for at-wavelength characterization of extreme-ultraviolet optics, APPL OPTICS, 40(25), 2001, pp. 4526-4533
We describe the experimental evaluation of a shearing interferometer concep
t for at-wavelength testing of extreme-ultraviolet optics. The concept is b
ased on the Ronchi test, which has been modified by a new design for entran
ce and exit gratings to suppress disturbing higher-order interference patte
rns. The interferometer concept has been tested on an experimental setup, o
f which all relevant parameters have been scaled from extreme-ultraviolet t
o visible-light wavelengths. A Twyman-Green interferometer has been integra
ted into the setup for comparison with the improved Ronchi test. A systemat
ic difference of 7-12 m lambda rms has been found between wave fronts measu
red with the improved Ronchi test and with the Twyman-Green interferometer.
Possible error sources have been analyzed. The accuracy of the interferome
ter is estimated to be 10 m lambda rms. (C) 2001 Optical Society of America
.