An Online Dynamic Amplitude-Correcting Gradient Estimation Technique to Align X-ray Focusing Optics

TL;DR

This paper introduces an online, adaptive gradient estimation method to precisely align X-ray focusing optics in fluctuating XFEL beamlines, improving automation over traditional stochastic approaches.

Contribution

The paper proposes a novel dynamic amplitude-correcting gradient estimation technique combining finite difference stencils and time-dependent sampling for optical alignment.

Findings

Effective lateral alignment demonstrated in simulation

Error expectation analysis confirms robustness

Method outperforms classic stochastic approaches

Abstract

High-brightness X-ray pulses, as generated at synchrotrons and X-ray free electron lasers (XFEL), are used in a variety of scientific experiments. Many experimental testbeds require optical equipment, e.g Compound Refractive Lenses (CRLs), to be precisely aligned and focused. The lateral alignment of CRLs to a beamline requires precise positioning along four axes: two translational, and the two rotational. At a synchrotron, alignment is often accomplished manually. However, XFEL beamlines present a beam brightness that fluctuates in time, making manual alignment a time-consuming endeavor. Automation using classic stochastic methods often fail, given the errant gradient estimates. We present an online correction based on the combination of a generalized finite difference stencil and a time-dependent sampling pattern. Error expectation is analyzed, and efficacy is demonstrated. We provide a proof of concept by laterally aligning optics on a simulated XFEL beamline.