O1.3 - Sensitive measurement of partial coherence using a pinhole array

SENSOR+TEST Conferences 2009
2009-05-26 - 2009-05-28
Congress Center Nürnberg
Proceedings OPTO 2009 & IRS² 2009
OPTO 1 - Interferometry
P. Petruck, R. Riesenberg - Institute of Photonic Technology, Jena, Germany, R. Kowarschik - Friedrich-Schiller-University Jena, Jena, Germany
35 - 40


For applications which require partially coherent light, e.g. in miniaturized interference setups like microimaging systems, the area of spatial coherence should fit to the optical design. For example, we apply partial coherence to lenseless inline holographic microscopy. Even if high coherent sources are suitable for the requirements of interference, a high degree of coherence is responsible for many disturbing effects within the optical system. Especially statistical interferences due to rough surfaces, so called speckles, are generated by coherent light. Unwanted reflections from optical surfaces and their interferences limit the quality of measurement.
An area of coherence can be defined as an area of featured interferences. The coherence volume can be defined as the product of the coherence length and the area of coherence. It is helpfull to use light sources with coherence volumes which correlate with the dimension of the setup itself. When only a small coherence volume is required, even partial coherent light sources, like halogen lamps or mercury lamps, are qualified to comply with the requirements of interference. Therefore it is necessary to determine the degree of coherence of those partially coherent light sources.
Spatial coherence is measured by Young’s double slit interferometer. The measurement range is given by the pinhole distance and the throughput is given by the pinhole diameters. In the case of small areas of spatial coherence this setup is limited in sensitivity. A sensitive measurement and management of partial spatial coherence is often necessary. The current task is to develop an interferometer for a much more sensitive measurement of partial spatial coherence with an extended measurement range for small areas of spatial coherence.