Spatial frequency self-filtering and brightness adaption of incoherently illuminated objects

Ernst Ulrich Wagemann; Hans J. Tiziani

doi:10.1117/12.360982

9 September 1999 Spatial frequency self-filtering and brightness adaption of incoherently illuminated objects

Ernst Ulrich Wagemann, Hans J. Tiziani

Proceedings Volume 3823, Laser Metrology and Inspection; (1999) https://doi.org/10.1117/12.360982
Event: Industrial Lasers and Inspection (EUROPTO Series), 1999, Munich, Germany

Abstract

In this paper an all-optical combination of coherence conversion and spatial frequency self-filtering using two optically addressed liquid crystal (OALC) is presented. A periodic object to be inspected is illuminated by a white light source, imaged onto a OALC and modulates its polarization properties. The OALC then modulates a coherent read-out beam, which can be Fourier transformed to enable frequency self-filtering. Self-filtering uses an additional OALC and is able to detect defects in periodic images. It is independent of the position or rotational orientation of the object and therefore a promising approach for a real-time assembly line inspection. We present experimental results for this cameraless processor and compare it to an alternative approach using a CCD camera and a Matrix-LCD for coherence conversion. In addition adaptive brightness regulation by an OALC in an intermediate image plane is a promising tool for image pre-processing. This adaption process reduces shiny local spots and brightens dark areas. Theory on brightness adaption using an OALC is given and some experimental results are discussed.

Citation Download Citation

Ernst Ulrich Wagemann and Hans J. Tiziani "Spatial frequency self-filtering and brightness adaption of incoherently illuminated objects", Proc. SPIE 3823, Laser Metrology and Inspection, (9 September 1999); https://doi.org/10.1117/12.360982

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KEYWORDS

Inspection

LCDs

Spatial frequencies

Liquid crystals

Modulation

Coherence (optics)

Crystal optics

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