Compact metrology beamline for EUV optic and adaptive optic tests (Conference Presentation)

Abstract

With the progresses achieved on the development of high quality, highly coherent soft X-ray (or EUV) sources from synchrotrons, free-electrons laser, high harmonics and plasma based soft X-ray laser, as well as for the need of always better optics for imaging (EUV lithography, EUV spatial telescopes, EUV microscopes), the demand on metrology is increasing very fast. Nowadays, many synchrotrons have developed metrology beamlines but with the limit of being too expensive and too large for transposing them to university-scale laboratories or optical firms. At Laboratoire d'Optique Appliquee, we have developed a compact and versatile metrology beamline to test at-wavelength different EUV optics, from single component to full assembly and adaptive optics. The beamline is based on the use of high harmonics generated by the interaction of a 35 fs, 4 kHz, 3 mJ laser with neutral gases. The high harmonics span from 10 to 50 nm and are fully coherent, collimated and exhibit a good wavefront of about lambda/5 rms. The beamline covers a footprint of about 5*1.5 m2 while the driving laser occupies about 4 m2. Itis composed of an interaction chamber where high harmonics are generated, a spectrometer and the metrology chamber (1.5m*0.7m) . We have tested many optical components from flat or curved mirrors to toroidal mirror or Schwarzschild microscope. We will present in detail the beamline as well as results from optic metrology. The beamline is also used for calibration of wavefront sensors. This beamline is well suited for testing EUV adaptive optic in any configurations.