• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.40-45
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• 2004

Recently, aspheric optical lenses and mirrors, which are harder to manufacture and measure than the conventional spherical ones, are widely used, particularly in electronic fabrication process. Generally, interferometric optical method is used for the measurement of spherical optical surface. However, the interferometric method for aspheric surface measurement is difficult because it needs a precise null corrector and strict environmental conditions such as constant temperature, humidity and vibrations. We have been studied on the manufacturing of aspheric optics to improve the surface profile accuracy and productivity using a corrective polishing process. For the corrective polishing, a practical method of On-Machine Measurement (OMM) is required. For this purpose, an optical OMM system has been studied using the Shach-Hartmann test, which is very robust to the practical polishing environment. The wavefront has been reconstructed from the measured data using the primary aberration polynomial function by the least squares fitting. The measured result of the OMM system shows that the maximum deviation is less than 200 nm for the one of commercial Fizeau interferometer Wyko 6000.

• Korean Journal of Optics and Photonics
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• v.15 no.3
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• pp.241-247
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• 2004

The collimator is necessary for the assembly and evaluation of high resolution satellite telescope. Traditionally, the off-axis paraboloid has been used as a collimator. However, it has some disadvantages in that it can suffer from air turbulence when the focal length of a collimator is long, which may result in some error in the measurement. In contrast, since the Cassegrain type collimator folds the beam, it occupies smaller space compared to the off-axis paraboloid for the same focal length. This can reduce the air turbulence, which can improve the measurement accuracy. In this paper, we explain the process of design and manufacturing of a diameter 450 mm Cassegrain type collimator, to evaluate the diameter 300 mm satellite telescope. After assembly of primary and secondary mirrors, the final wavefront error of the collimator was 0.07λ(λ=633 nm), which is the diffraction limit.

• Korean Journal of Optics and Photonics
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• v.24 no.6
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• pp.318-323
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• 2013

Digital holographic microscopy allows optical path difference measurement. Optical path difference depends on both the refractive index and the morphology of the sample. When interference fringes are very closely spaced, the phase data contain high frequencies where $2{\pi}$ ambiguities cannot be resolved. The immersion testing method, which is a transmission test while the sample is immersed in liquid, is very effective in reducing high frequency fringes in transmission measurements so that large dynamic range testing is possible for a non-null configuration. We developed a digital holographic microscope using liquid that can measure the high numerical aperture aspheric morphology of a sample. This system provides highly precise three-dimensional information on the sample. By improving the experimental method, choosing liquids which have similar refractive index to the sample, we can measure more accurate three-dimensional information on the samples.