Modular Soft X-Ray Emission Spectrograph

Abstract

We have been developing the Hettrick-Underwood type soft x-ray spectrograph for over a decade. This optical design uses one spherical mirror for focusing x-rays onto the CCD detector and a set of variable line-spacing gratings for energy analysis. Unlike the previous effort carried out at the ALS, what we have achieved in the current design is to incorporate the concept of modularity. The model of spectrograph is shown below. It contains three major components: the optics chamber and downstream section (detector plus driving mechanism using a swing arm pivoted at the grating location, see figure) for inside and outside order (translation stage without swing arm, not shown here). Inside order design is often used when source size is larger than the detector pixel resolution, while the outside order is used when source size is smaller than the detector pixel resolution. Irrespective to which order is selected, there is no change in the mechanism of optics chamber. The location of optics chamber relative to the source and detector can also be changed to optimize the energy resolution at target photon energy. The incident angles on mirror and gratings can be varied, in conjunction with the grating line densities, to balance the resolution and throughput. The internal components of optics chamber are also modular and changing the dimension of optics can be done by using different holders. The modularity not only greatly reduces the design and assembling effort, but also offers the cost benefit. Although the cost of this type of spectrograph is expected to be higher than XES350, it is still significant lower than the one-of-the-kind design used at every synchrotron facilities. The unique flexibility and modularity not only allows the users to tailor the design of spectrograph for the characteristic of their sources, but also to have cost down in standardizing the fabrication parts.