ABSOLUTE INTERFEROMETRIC TEST FOR HIGH NUMERICAL-APERTURE SPHERICAL CONCAVES: GRAVITATIONAL EFFECT |
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| Kenichi Hibino, Ryohei Hanayama, Kim Yangjin |
- Abstract:
- Spherical concaves with high numerical apertures are required in industry for lithography optics in ultraviolet (UV) and X-ray wavelengths. Systematic error in the interferometric test of these surfaces are aberrations due to imperfect alignment, gravitational effect, geometrical effect of nonuniform phase shift, aberrations of converging optics, phase-shift nonlinearity, mechanical vibration, and so on. Gravitational deformation of a 4-inch spherical concave surface was measured in a vertical Fizeau interferometer. Aberrations caused by the deformation was separated and extracted from the total deviations of a sphericity measurement in an absolute test of two spherical comparisons. After subtracting the gravitation deformation from the shape of the spherical concave, we can define a neutral surface which is free from gravity. The gravitational sag in a horizontally placed spherical surface could be measured if we measure the difference of surface shape deviation from this neutral shape. Dominant alignment errors, coma and spherical aberrations were estimated numerically. Experimental results show that the aberrations caused by gravity amount to 7 nm peak-to-valley (PV).
- Keywords:
- spherical test, fizeau interferometer, phase measurement, gravitational deformation, phase shift
- Download:
- IMEKO-TC14-2014-10.pdf
- DOI:
- -
- Event details
- IMEKO TC:
- TC14
- Event name:
- TC14 LMPMI Symposium 2014
- Title:
11th Symposium on Laser Metrology for Precision Measurement and Inspection in Industry
- Place:
- Tsukuba, JAPAN
- Time:
- 03 September 2014 - 05 September 2014