A method of surface figure measurement is described based on the transmitted wavefront of an optical element obtained from a Mach-Zehnder interferometer. Given known values for the refractive index and center thickness, along with the sample's transmitted wavefront, the unknown surface profile is reconstructed in a deterministic way. The technique relies on knowledge of one of the surfaces of the element, such as an easy-to-measure plano or spherical surface, and is well suited for testing aspheric surfaces. Reverse raytracing is used to bring the transmitted wavefront from the detector to the unknown surface considering the refraction at the surfaces in the system. Reverse raytracing also removes the effects of transmission through a thick lens and the induced aberration associated with the interferometer. In the interferometer, the wavefront transmitted through the sample is tested against a plano reference. This method also has the ability to make measurements on multiplexed surfaces, such as a lenslet array, which traditionally cannot be measured without moving the sample. The surface profile of a plano-convex lens has been produced and verified against other metrology techniques for calibration purposes. Surface measurements on a cylindrical lens and a lenslet array are also presented.
A method of surface figure measurement is described based on the transmitted wavefront of an optical element
obtained from a Mach-Zehnder interferometer. Given known values for the refractive index and center thickness,
along with the samples transmitted wavefront, the unknown surface profile is reconstructed in a deterministic
way. The technique relies on knowledge of one of the surfaces of the element, such as an easy to measure plano or
spherical surface, and is well-suited for testing aspheric surfaces. Reverse raytracing is used to remove the effects
of transmission through a thick lens and to remove induced aberration associated with the interferometer. In
the interferometer, the wavefront transmitted through the sample is tested against a plano reference. In order to
reduce the high frequency fringe content of the interferogram, the sample can be tested in an immersion solution.
This method also has the ability to make measurements on multiplexed surfaces, such as a lenslet array, which
traditionally can not be measured without moving the sample. The surface profile of a plano-convex lens has
been produced and verified against other metrology techniques for calibration purposes. Surface measurements
on a lenslet array are also presented.
KEYWORDS: Birefringence, Optical discs, Digital video discs, Polymers, Digital video recorders, Data storage, Optical properties, Temperature metrology, Optical engineering, Diamond
It is necessary to improve optical, geometrical, and mechanical properties in the optical disk substrates as the information storage devices with high storage density using short wavelength lasers are being developed. However, the conventional injection molding process is no longer appropriate for producing the high-density information storage optical disk substrates with superb optical, geometrical, and mechanical properties. It is, therefore, inevitable to develop new concepts for the molding processes. In the present study, DVD-RAM substrates were fabricated by injection-compression molding, which is regarded as the most suitable process to manufacture optical disk substrates. The effects of various processing conditions on the birefringence distribution, the land-groove structure including the groove depth and the surface roughness of the land, and the radial tilt were examined experimentally. It was found that the birefringence, which is regarded as one of the most important optical properties for optical disk, was very sensitive to the mold wall temperature history. Also, the integrity of the replication, represented by the land-groove structure, and the radial tilt were influenced mostly by the mold temperature and the compression pressure.
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