Stability evaluation of a double crystal monochromator using an optical linear encoder

A dedicated jig with an optical linear encoder was developed to evaluate the pitching stability between the first and second crystals of a double crystal monochromator in a standalone configuration. This method does not require synchrotron radiation, enabling direct assessment of the monochromator's intrinsic stability. Unlike beamline-based measurements influenced by upstream optics, this approach isolates the monochromator's performance. Designed and implemented by Kohzu Precision, the system is currently applied to a symmetrical layout monochromator to assess angular stability in mechanically decoupled configurations. The encoder counter supports readout rates up to 12 MHz; however, considering the latch interval of the system, the effective sampling rate is about 5 kHz. Measurements were conducted at approximately 2 kHz. At a Bragg angle of 10 degrees, the angular stability (RMS) in the pitching direction was better than 20 nrad, and a dominant vibration peak was observed near 180 Hz. These results demonstrate the system's effectiveness in characterizing the stability of high-performance monochromator configurations.