A two-crystal x-ray monochromator was built at LNLS. It is based on the Golovchenko [J. A. Golovchenko, R. A. Levesque, and P. L. Cowan, Rev. Sci. Instrum. 52, 51 (1981)] geometry with one rotation and two translations in order to tune the wavelength and keep constant the position of the monochromatic beam, respectively. The Bragg angle can vary from 10° to 80° using a standard high precision external goniometer whose minimum step is 0.001°. The two translations are based on a leaf spring device, with a maximum wobbling of ±2 arcsec along 50 mm. Fine tuning between the two crystals and detuning for harmonic rejection are produced by elastic devices using the magnetic force between a permanent magnet and a solenoid acting on a weak link of the second crystal. The monochromator housing is vacuum compatible. The equipment was tested using a conventional x-ray source and a standard control system. It will be used associated with classical extended x-ray absorption fine structure (EXAFS) and the high precision x-ray optics experimental station.
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Corrêa et al. (1992) studied this question.
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