Meaning
Optimization of optical alignment ensures that the interference patterns generated by radiation passing through a sample accurately represent the density variations of the material. Phase contrast calibration involves adjusting the relative positions of the source and detector to optimize the visibility of phase shifted signals. This step is essential when imaging low density materials like battery polymers that do not absorb radiation strongly.
Correct alignment prevents the introduction of artificial halos that could obscure the true microstructural features.
Wavefront Alignment
Coherence of the radiation source defines the quality of the phase information that can be recovered. The phase contrast calibration process checks the spatial and temporal coherence to ensure that the wavefront remains stable during the entire exposure. Misalignment leads to a loss of resolution and a reduction in the signal to noise ratio.
Detector Response
Sensitivity of the imaging sensor must be mapped to account for variations in pixel performance across the array. Phase contrast calibration includes the collection of flat field and dark field images to normalize the detector output. This normalization removes artifacts caused by dust on the optics or inherent manufacturing differences in the sensor pixels.
Fringe Optimization
Geometric parameters of the experimental setup dictate the width and intensity of the edge enhancement effects. By varying the propagation distance between the sample and the detector, the phase contrast calibration identifies the setting that provides the sharpest contrast without excessive distortion. This balanced setting allows for the clear identification of interfaces between different chemical phases within a battery cell.
Regular execution of this procedure is required to maintain the quantitative accuracy of the reconstructed density maps.
