Robust One-shot Short Coherence Interferometry ROSI

The 'robust one-shot interferometry' (ROSI)  has been optimized in several aspects and now offers a miniaturized, robust and long-term stable as well as high-precision point and line profile measurement at very high measurement and evaluation speeds.

• Very high measuring and evaluation speed
• Long-term stability, fast & highly accurate point and line profile measurement, the latter in perspective
• Inexpensive, compact and very robust design
• Evaluation of the phase information provides resolution in the nm range for profile measurement

Researchers at the Institute for Technical Optics, Univer­sity of Stuttgart, succeeded in developing a sensor design and method for extremely robust one-shot interferometry (‘ROSI’), which is currently being further optimized. It is now possible to achieve higher measurement speeds, while ensuring a high level of robustness. As a result, the ROSI approach now offers a decisive advantage, espe­cially for demanding applications such as inline inspection under production conditions.

Optical metrology allows for contactless and non-destruc­tive analysis of an object’s metric and spectral properties, covering a broad range of sizes. For example, intensity, contrast, polarization or wavelength can be measured at as many points of an object as required. However, in order to be able to reliably determine the actual target size, a robust and powerful system is needed in addition to efficient algo­rithms.

Interferometry has become an established optical profile measurement method. Chromatic-confocal spectral inter­ferometry (CCSI), for example, provides a very good basis for single-shot applications by combining interferometry with confocal microscopy. However, this approach requires a spectrometer and sophisticated data evaluation, which, in turn, can have a limiting effect on the measurement speed.

Compared to CCSI, ‘ROSI’ allows for the generation of robust one-shot data sets in the form of spatial interfero­grams. For this purpose, it uses a two-beam interferometer with special components, such as a novel three-plane mir­ror reference end reflector, which can be produced by ultra-precision diamond machining. The well-known and well proven algorithms of white light interferometry can be used for data evaluation. Precise high-resolution profile data can thus be captured at high speed down to the nanometer range using phase information.
The system has been extended by a new application of retroreflection. Thanks to the ‘interferometric gain’, it en­ables users to measure less cooperative or non-coopera­tive surfaces at the lowest level of reflection. In addition, absolute measurement of a 3D object space would be pos­sible by combining the system with 3D coordinate measur­ing technology.

https://iopscience.iop.org/article/10.1088/1361-6501/aa52f1