Controlling X-ray emission with optical nanostructures

TL;DR

This paper demonstrates how optical nanostructures can be used to manipulate and enhance X-ray/optical nonlinear processes, enabling new control over X-ray emission for advanced imaging and spectroscopy applications.

Contribution

It introduces a quantum theoretical framework for controlling X-ray nonlinear interactions using optical nanostructures, specifically photonic crystals, to shape X-ray emission.

Findings

Achieved a 2.2-fold rate enhancement in X-ray emission using photonic crystals.

Controlled the spectral and spatial characteristics of X-ray emission.

Proposed applications include monochromatic X-ray sources and enhanced imaging techniques.

Abstract

Nonlinear processes lie at the heart of many technologies such as frequency converters and entangled photon sources. Historically, observation and manipulation of these processes, for instance through nanostructures, has been limited to optical and lower frequencies. Recently, however, second-order nonlinear processes which couple X-ray and optical photons have been observed and used to probe the electronic structure and optical response of materials. Observing and controlling these processes remains challenging due to their low efficiency and the difficulty of fabricating devices with spatial features on the scale of X-ray wavelengths. Here, we show how optical nanostructures can be used to manipulate X-ray/optical nonlinear processes, using a quantum theory which describes these second-order nonlinear interactions. As an example, we show how photonic crystals shape both the spectral and spatial characteristics of X-rays emitted through X-ray to optical parametric down-conversion, leading to a fill-factor-normalized rate enhancement of 2.2 over an unstructured medium, in addition to control over the directionality of X-ray emission. The ability to control X-ray nonlinear processes may lead to more monochromatic, heralded X-ray sources, enhanced ghost imaging of lattice and electronic dynamics, and imaging and spectroscopy beyond the standard quantum limit. Our framework illuminates a path towards controlling quantum optical effects at X-ray frequencies.