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Digital Holography and Its Application in MEMS/MOEMS Inspection
Published in Wolfgang Osten, Optical Inspection of Microsystems, 2019
Wolfgang Osten, Pietro Ferraro
In interference microscopy, this problem is solved experimentally by inserting into the setup the same microscope objective (MO) in the reference arm, at an equal distance from the exit of the interferometer. This arrangement, called a Linnik interferometer, requires that if any change has to be made in the object arm, then the same change must be precisely reproduced in the reference arm in such a way that the interference occurs between similarly deformed wavefronts. As a consequence, the experimental configuration requires a very high degree of precision. Another option is the Mirau interferometer; however, it is difficult to achieve high-resolution imaging with this technique, because a miniaturized interferometer must be inserted between the sample and the MO. It is important to point out that, in contrast to conventional approaches, DH allows the direct calculation of the complex wavefront, in phase and intensity, by the numerical solution of the diffraction problem in the computer.
Thickness Measurement
Published in Rajpal S. Sirohi, Introduction to OPTICAL METROLOGY, 2017
There could be several other types of interferometers that could be used for low coherence interferometry. In the Linnik interferometer, two matched microscope objectives are used. While one objective focuses the laser beam on the sample, the other focuses the laser beam on a reference mirror. An elegant method is to use a Mirau objective, which in itself is an equal path interferometer, and hence, white- light fringes are easily obtained. The objective can be focused on the upper and lower interfaces and the displacement of the objective, when multiplied by the refractive index of the film, gives its optical thickness.
Two-dimensional modelling of systematic surface height deviations in optical interference microscopy based on rigorous near field calculation
Published in Journal of Modern Optics, 2020
Tobias Pahl, Sebastian Hagemeier, Lucie Hüser, Weichang Xie, Peter Lehmann
In principle, the model consists of two parts, the FEM simulation of the scattered near field and the subsequent modelling of the measurement instrument and process. In the first part of this section, the FEM model is presented assuming the measurement object to be a grating. The second part includes the Fourier optics approach describing the measurement instrument, which in our case is a Linnik interferometer [6,44] as depicted in Figure 1(a). The light source is assumed to be spatially incoherent, due to the Köhler illumination used in the interferometer [45]. The system is supposed to be ideal and aberrations are not taken into account. Aberrations could be included analogous to Section 4 in [6].