Laboratório Nacional
de Luz Síncrotron

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TÉCNICAS

VOLTAR

TÉCNICAS DISPONÍVEIS


As técnicas e configurações experimentais a seguir estão disponíveis nesta linha de luz. Para saber mais sobre as limitações e requerimentos das técnicas, contate o coordenador da linha de luz antes de submeter sua proposta.

TOMOGRAPHY


Tomography is a non-invasive imaging technique that allows to examine slices of a sample without damaging it. While radiography provides an image from a single orientation of the sample, tomography provides many images of the sample from different orientations, resulting in a set of projections or sinograms.  Essentially, each sinogram column corresponds to the X-ray projection at one angle. This data can then be reconstructed by basically solving the inverse Radon transformation.

In our case, filtered back projection is used to reconstruct 3D images from a series of 2D projections. The projection values are smeared back across the 2D projections and integrated across all angles. To reduce blurring effects, the images are filtered in Fourier space before being back projected.

 

PHASE CONTRAST - PROPAGATION


Similar to tomography, this method involves placing the detector some distance from the sample, so that the radiation refracted from the sample can interfere with the unchanged beam. Given the high degree of coherence available in synchrotron radiation, interference patterns or Fresnel fringes can be observed some distance away from the sample. Using this technique allows us to enhance the contrast observed in absorption images or separate entirely the phase (phase retrieval) and attenuation components. This method is particularly useful when investigating light materials or biological samples or even composites made from similar materials.

 

PHASE CONTRAST - GRATING BASED


This technique is based on the Talbot effect, which is a Fresnel diffraction effect and leads to repetition of a periodic wavefront after a certain propagation distance, called the Talbot length. By placing a phase grating behind the sample, the interference pattern of the Talbot effect is modified by absorption, refraction and scattering in the sample. This interference pattern can then be analysed using a second absorption grating, which transforms the local fringe position into signal intensity variation on the detector. Along with the conventional transmission image of a sample, it provides both a differential phase contrast and a dark field image of the sample, by stepping the phase grating over a single period. Applications range from medical imaging of soft tissues, to food screening and measuring short range order in mesoscale systems.