Exploiting the whole information content of the light field: Limitations and approaches
In the context of measurement technology, optical methods have a number of unique features. To them belong in particular the non-contact and high speed interaction with the object under test, the largely free scalability of the dimension of the probing tool, the high resolution of the data, the diversity of information channels in the light field, and the flexible adaptability of the comparative standard. On the other hand, the user is also confronted with a bunch of challenges. Here one should mention especially the indirect nature of the measurement. This fact is the origin of a number of serious consequences which make it often difficult for the practitioner to decide for optical metrology. However, the numerous information channels recommend optical principles for the solution of various inspection and measurement problems. A broad variety of techniques is sensitive for the measurement of a particular quantity such as the intensity, the frequency, the phase, the angular spectrum, the polarization state, the angular momentum, the degree of coherence and the time of flight. By applying these methods a wide spectra of quantities can be evaluated. To them belong dimensional, structural, geometrical, colorimetrical, chemical, and mechanical properties of the object under test. More modern principles such as hyper-spectral technologies are designed to measure various modalities with one system. Known under the name of multimodal measurement techniques, these systems are capable of elegantly solving complex medical, structural-mechanical or biological problems. However, the high information density in optical signals is often not only an advantage but a challenge with respect to the correct interpretation of the measured data. This talk starts with a brief summary of the advantages and disadvantages of optical metrology. Afterwards we discuss the various information channels and present examples for their exploitation. Special attention is directed to the correct interpretation of the data.