Performance Testing of a Large-Format Reflection Grating Prototype for a Suborbital Rocket Payload

TL;DR

This paper reports on the testing of a large-format reflection grating prototype for a soft X-ray spectrometer on a suborbital rocket, demonstrating it meets resolution requirements and discussing measurement limitations.

Contribution

It presents the fabrication and performance testing of a novel reflection grating prototype using Bayesian analysis, highlighting the potential for higher resolution than measured.

Findings

Achieved the required spectral resolution with >94% confidence

Bayesian modeling suggests the actual resolution may exceed measured limits

Test setup limitations may have constrained the measurement of the grating's true performance

Abstract

The soft X-ray grating spectrometer on board the Off-plane Grating Rocket Experiment (OGRE) hopes to achieve the highest resolution soft X-ray spectrum of an astrophysical object when it is launched via suborbital rocket. Paramount to the success of the spectrometer are the performance of the $>250$ reflection gratings populating its reflection grating assembly. To test current grating fabrication capabilities, a grating prototype for the payload was fabricated via electron-beam lithography at The Pennsylvania State University's Materials Research Institute and was subsequently tested for performance at Max Planck Institute for Extraterrestrial Physics' PANTER X-ray Test Facility. Bayesian modeling of the resulting data via Markov chain Monte Carlo (MCMC) sampling indicated that the grating achieved the OGRE single-grating resolution requirement of $R_{g}(\lambda/\Delta\lambda)>4500$ at the 94% confidence level. The resulting $R_g$ posterior probability distribution suggests that this confidence level is likely a conservative estimate though, since only a finite $R_g$ parameter space was sampled and the model could not constrain the upper bound of $R_g$ to less than infinity. Raytrace simulations of the system found that the observed data can be reproduced with a grating performing at $R_g=\infty$. It is therefore postulated that the behavior of the obtained $R_g$ posterior probability distribution can be explained by a finite measurement limit of the system and not a finite limit on $R_g$. Implications of these results and improvements to the test setup are discussed.