Abstract
We present a Mirau-type coherence scanning interferometer (CSI) with an oscillating reference mirror and an integrated interferometric distance sensor (IDS) sharing the optical path with the CSI. The IDS works simultaneously with the CSI and measures the distance changes during the depth scanning process with high temporal resolution. The additional information acquired by the IDS is used to correct the CSI data disturbed by unwanted distance changes due to environmental vibrations subsequent to the measurement. Due to the fixed reference mirror in commercial Mirau objectives, a Mirau attachment (MA) comprising an oscillating reference mirror is designed and built. Compared to our previous systems based on the Michelson and the Linnik interferometer, the MA represents a novel solution that completes the range of possible applications. Due to its advantages, the Mirau setup is the preferred and most frequently used interferometer type in industry. Therefore, the industrial use is ensured by this development. We investigate the functioning of the system and the capability of the vibration compensation by several measurements on various surface topographies.
Highlights
Optical topography sensors such as scanning confocal microscopes (SCM) [1] and coherence scanning interferometers (CSI) [2,3] are well-established measuring instruments in industry and research for the contactless inspection of surface topographies with height structures in the micro- and nanometer range
A CSI comprising a Mirau objective is introduced, where a custombuilt interference device is attached to a commercial microscope objective
The changed distance between CSI and surface under investigation including influences caused by external vibrations are measurable by the interferometric distance sensor (IDS)
Summary
Optical topography sensors such as scanning confocal microscopes (SCM) [1] and coherence scanning interferometers (CSI) [2,3] are well-established measuring instruments in industry and research for the contactless inspection of surface topographies with height structures in the micro- and nanometer range. As the depth of field is required to cover the whole height range of the specimen, the lateral resolution and axial accuracy are usually worse compared to CSI, e.g., in case of the approach presented in [5] the lateral resolution is specified by 30 μm for an NA of 0.28 and exceeds the Rayleigh resolution of the system Another approach is given by the usage of an additional laser interferometer besides the main measuring system, the output of which is used to actively compensate for deflections caused by environmental vibrations [7,8,9,10]. In order to reduce the effect of noise, Kiselev et al [12] correlate the measured interferogram with a nominal one Another promising approach for passive vibration compensation in CSI is the use of an interferometric distance sensor (IDS) integrated in the optical path of the CSI setup. A conclusion is drawn in Section 5 and an outlook to further investigations will be given
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