Optical surface metrology with spatially and temporally partially coherent light wave fields, Application transfer (OPaL:Transfer)

• Applicants: Professor Dr. Ralf Bernhard Bergmann; Dr.-Ing. Gerd Ehret
• Subject Area: Measurement Systems
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 460789164

The areal optical shape detection of freeform optics is an essential prerequisite for quality assurance in the optical industry. In particular, the cost-effective, precise and flexible measurement of aspheres still represents an unsolved challenge. Within the scope of the research project OPAL funded by the DFG and its continuation OPAL II, methods based on shear interferometry were investigated in relation to the detection of freeform surfaces. With the Multiple Aperture Shear Interferometry (MArS), a method was developed which allows the simultaneous use of several independent light sources. This makes it possible, despite a restricted acceptance angle of the imaging optics, with a corresponding distribution of the light sources, to completely capture not only spherical but also aspherical test objects with a relatively large diameter. In this way, the approach combines the large illumination aperture and flexibility of geometrical-optical methods such as deflectometry with the high precision of interferometric methods. Measurements in transmission and reflection showed the potential of MArS.The approach is now to be further developed into a prototype within the framework of this transfer project by the partners of the OPAL predecessor projects together with the Mahr GmbH company. The overall goal of the project is to test the approach described above in a practice-oriented environment and to further develop it into a corresponding measurement system in the context of an exemplary application. For the implementation in an application, it is of particular interest which test object types can be measured, how far the measuring time can be reduced and how complex the setup process and handling are.In order to achieve the project goal, it is necessary to determine the limits of the adaptability of the MArS measuring arrangement to relevant applications. Important practice-oriented guidelines are the recording of as different types of test objects as possible, the achievement of short measurement times, ease of operation and cost aspects. This results in the following sub-goals for the project: The experience from the previous projects must be used to adapt measurement arrangements to relevant application scenarios and to implement corresponding demonstrators, whereby measurements should be made on aspherical test objects with diameters of up to 76 mm (3 "). For this purpose, an efficient measurement and evaluation process with a measurement time of less than 5 minutes and a set-up process that uses as few reference objects as possible must allow measurements on as different types of test objects as possible. The calibration process to be implemented should enable the measurement uncertainty to be reduced to below 50 nm using standard optics in the imaging system.

• DFG Programme: Research Grants (Transfer Project)
• Application Partner: Mahr GmbH