Analytical Alignment Tolerances for Off-Plane Reflection Grating Spectroscopy

TL;DR

This paper develops an analytical framework for determining alignment tolerances of off-plane reflection gratings in X-ray spectrometers, crucial for maintaining spectral resolution and efficiency in future space telescopes.

Contribution

It introduces a comprehensive analytical formulation for all six degrees of freedom in grating alignment, validated by raytrace simulations, to optimize spectrometer performance.

Findings

Analytical tolerances accurately predict misalignment effects.

Misalignments significantly impact spectral resolution and efficiency.

Raytrace simulations confirm the analytical model's validity.

Abstract

Future NASA X-ray Observatories will shed light on a variety of high-energy astrophysical phenomena. Off-plane reflection gratings can be used to provide high throughput and spectral resolution in the 0.3--1.5 keV band, allowing for unprecedented diagnostics of energetic astrophysical processes. A grating spectrometer consists of multiple aligned gratings intersecting the converging beam of a Wolter-I telescope. Each grating will be aligned such that the diffracted spectra overlap at the focal plane. Misalignments will degrade both spectral resolution and effective area. In this paper we present an analytical formulation of alignment tolerances that define grating orientations in all six degrees of freedom. We verify our analytical results with raytrace simulations to fully explore the alignment parameter space. We also investigate the effect of misalignments on diffraction efficiency.