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Atlas Technologies Soft X-Ray Modular X-Ray Spectrometer

Lawrence Berkeley Laboratory has licensed Atlas Technologies to provide the mechanical and UHV experience to fabricate devices.

The modular mechanical design of MXS allows it to be reconfigured to operate in high-resolution and/or high-throughput mode for different applications it is designed to address these issues by modularizing the key components while maintaining the ability to achieve high resolving power and high detection efficiency.

Using resonant inelastic x-ray scattering spectroscopy (RIXS), and the capability to vary the momentum transfer (q) as-well-as to analyze the energy loss (ΔE) in the process, the momentum-resolved RIXS (or qRIXS) has been used to measure the dispersion relations of low energy collective modes, such as phonons, magnons and orbitons, that are critically linked to the emergent material properties such as, high temperature superconductivity, and colossal magnetoresistance and multiferroicity

Atlas recently supplied spectrometer to SLAC and PAL Korea. Atlas’ goal is to offer the spectrometer to end-stations in labs around the world and conceivably to be used with lab based soft x-ray sources that have modest focusing capability.

Basic Design

Based upon experience from several years of use with similar designs at the ALS, the design is based on the Hettrick-Underwood design two optical elements used in the X-ray emission spectrograph a spherical mirror for focusing the X-rays onto an in-vacuum CCD detector and a variable line spacing (VLS) plane grating for energy monochromatization. The grating is operated in the constant incident angle mode, thus variation in the detection photon energy is accomplished by moving the detector along the focal plane.

MXS-qRIX has two main components, optics chamber and a cantilevered swing arm detector assembly.

The optics chamber, The mirror and grating are mounted inside their own carriages that are driven by motorized feedthrough and stage through wire linkage. The relative position of mirror and grating poles can be adjusted by turning the fine-pitch screws on the back side of the substrates The ease of ex-situ adjustment allows the setting of mirror and grating angles and their positions using the high precision coordinate measuring machine (CMM) to stay within the installation tolerance. The mirror and grating carriages are mounted on a common U-shape aluminum backbone via flexures. Their angles can be changed dynamically by motorized feedthrough and stage. These motorized degrees of freedom will be extremely useful in the initial alignment phase and during the normal operation. The entire optics assembly is attached to a stainless steel top flange and is sealed inside the UHV aluminum chamber. A set of apertures in front of the mirror can be adjusted to block out the scattered x-rays from entering the spectrometer.

The detector assembly, Held inside a light-weight aluminum swing arm, a fly tube holds the 2D imaging detector mounted at the tube that is connected to the optics chamber by a big bellow. The bellows allows the detector angle and position to be changed while maintaining ultra-high vacuum (UHV). The swing arm fly tube assembly is supported by the brackets mounted on top of two translation stages that are driven by a motorized jack to change the detector angle relative to the horizon and move the detector along the optical path. This degree of freedom changes the distance between grating and detector, which is needed to correct the defocusing when MXS is recording photon energies far away from the nominal photon energy.

During the measurements, to detect x-rays with different photon energy, one only needs to change the detector angle and the distance between grating and detector to correct the defocusing.

Comparing Scientia model XES-350 to the Atlas MXS-qRIX-1000 Soft X-Ray Grating Based Spectrometer has resolving power of 1,000~5,000 (0.05eV ~ 0.2eV) The MXS can use all types of gratings, whether constant line spacing or varied line spacing, with different surface figures such as planar, spherical or even elliptical. Different types of gratings can have their respective strength and limitation, and being able to choose gratings freely with MXS will offer the optical designers the freedom to select the optical parameters.

On the other hand, XES 350 can only use fixed radius, constant line spacing spherical gratings. Although such gratings were easier and less expensive to produce decades ago, they cost almost the same as other types of gratings these days thanks to the advanced grating fabrication technology. MXS is a far more advanced design that takes full advantage of the grating fabrication technology.

XES 350 has a fixed optomechanical design with very little room for modification: the constant line spacing gratings have a fixed incidence angle and radius, and the optical parameters like source-to-grating and grating-to-detector distances cannot be easily changed. Even with small source beam (nominal 10 microns in the grating dispersive direction), the best resolving power (photon energy divided by the energy resolution) is only around 2,000.

MXS uses a high quantum efficiency CCD detector while XES 350 can only use a micro-channel plate coated with fluorescence coating at grazing incidence angle. There is almost an order of magnitude difference in the detection efficiency just from the detector. That is one reason why MXS is more efficient than XES 350

Reference: Lawrence Berkeley National Laboratory, R&D 100 entry information

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