1. Feature Of The Week 5/25/14: Exploiting Advanced Low Coherence Interferometric Imaging Techniques for Material Research Applications

    Feature Of The Week 5/25/14: Exploiting Advanced Low Coherence Interferometric Imaging Techniques for Material Research Applications

    Researchers of CDL MS-MACH, Johannes Kepler University Linz, Austria, have recently demonstrated time domain polarization-sensitive full-field optical coherence microscopy (PS-FF-OCM) and low coherence interferometric second harmonic generation microscopy (iSHGM-OCM), as two current modifications of FF-OCM and scanning OCM, for extending the application range of FF-OCM and SHG microscopy adapted for use in material sciences [1].

    The first technique, PS-FF-OCM, can simultaneously deliver reflectivity, retardation and (in-plane) optical axis information of birefringent materials as depth-resolved en-face information. Both amplitude and phase information in full field configuration are exploited by the applied demodulation scheme.

    In particular, this PS-FF-OCM technique has been developed for various polymer material testing tasks. The FF-imaging procedure was used for the investigation of lateral distribution of the birefringence and optical axis orientation in materials, such as a micro-structured photo-resist component which exhibits curing-induced internal stress-strain fields. Optical anisotropies and inhomogeneities can be determined hereby. Also the comparison to raster-scanning PS-OCT measurements for similar structures should be mentioned [2]. Furthermore, the formation/ extraction of spherolitic, birefringent micro-crystallites in extruded polypropylene sheets has been visualized in high resolution and represents an interesting extension to conventional PS-OCT schemes [3].

    The second technique, iSHGM-OCM, represents a raster-scanning probing method. It exploits – additional to the structural information obtained by conventional linear OCM – the harmonic signal caused by non-linear optical effects for providing specific contrast at distinguished SHG active sites. The system operates at 1550 nm using a compact fs-fiber laser for testing. The setup can be used in two configurations, as interferometric SHG microscope and as OCM, enabling multi-modal imaging. Due to coherent detection scheme parasitic effects, like multiphoton fluorescence, can be suppressed.

    In the field of material sciences, the applications for iSHGM are mainly related to the detection and characterization of corrosion products in the micron-scale range, such as representatively occurring at polymer-coated metallic surfaces. Here, in a non-destructive way, SHG active structures at interfaces can be extracted beneath the polymer coating layer. In the future such data can be helpful to directly monitor and better understand the progress of special corrosion processes, like filiform corrosion.

    For more information see [4,5]. Courtesy Bettina Heise from the Johannes Kepler University of Linz.

    [1] Heise, B. et al., Full Field Optical Coherence Microscopy: Imaging and Image Processing for Micro-Material Research Applications, in M. Kawasaki (ed.), Optical Coherence Tomography (InTech), 139-162, 2013.

    [2] Wiesauer, K. et al., Transversal ultrahigh-resolution polarization-sensitive optical coherence tomography for strain mapping in materials, Opt. Express 14, 5945-5953, 2006.

    [3] Hierzenberger, P. et al., In-situ OCT for Time - Resolved Investigation of Crystallization Processes in Polymers, Macromolecules 57(6), 2072-2079, 2014.

    [4] B. Heise et al., Simultaneous detection of optical retardation and axis orientation by polarization-sensitive full field optical coherence microscopy for material testing, Laser Phys. Lett. 11, 2014.

    [5] A. Prylepa et al., Low coherence interferometric second harmonic generation microscopy for non-destructive material testing using a broadband 1550nm fs-fiber laserr, Laser Phys. 24, 2014.

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