A novel beam width doubling double crystal monochromator -some preliminary findings

The maximum useable beam width at the Biomedical Imaging and Therapy (BMIT) beamline at the Canadian Light Source (CLS) is suitable for most imaging applications. But access to a wider beam would benefit many programs especially computed tomography where the beam width defines the largest sample that can be imaged. A double crystal bent Laue monochromator capable of doubling the width of the incident beam is proposed; this is possible by taking advantage of symmetric off-axis, or skew reflections in the crystals. A preliminary experiment to establish proof of concept for this design has been completed using a double crystal unbent Laue system. Results are presented showing the beam width doubling from 28.3mm to 56.6mm and the effect of the skew reflections on the monochromaticity of the exit beam. Further work on this monochromator will include an investigation into the choice of reflections, a study of the effect on the change in energy across the exit beam, the development of strategies to minimize the effect of the beam overlap region downstream from the monochromator and the development of an alignment process for the double crystal bent Laue system.