Correction of the X-ray wavefront from compound refractive lenses using 3D printed refractive structures
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-10-19 |
| Journal | Journal of Synchrotron Radiation |
| Authors | Vishal Dhamgaye, David Laundy, Sara J. Baldock, Thomas Moxham, Kawal Sawhney |
| Institutions | Raja Ramanna Centre for Advanced Technology, Science Oxford |
| Citations | 16 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: X-ray Wavefront Correction using MPCVD Diamond
Section titled âTechnical Documentation & Analysis: X-ray Wavefront Correction using MPCVD DiamondâExecutive Summary
Section titled âExecutive SummaryâThis analysis focuses on the research demonstrating X-ray wavefront correction using 3D printed refractive structures, highlighting the critical material limitations and positioning 6CCVDâs MPCVD diamond solutions as the necessary upgrade for high-flux applications.
- Core Achievement: A 3D printed polymer corrector plate successfully reduced the r.m.s. wavefront error of Beryllium (Be) Compound Refractive Lenses (CRLs) by a factor of six (from 14.4 pm to 2.4 pm).
- Methodology: The technique employed knife-edge imaging for at-wavelength wavefront sensing and Zernike polynomial expansion to quantify aberrations (e.g., spherical aberration, astigmatism).
- Material Limitation: The polymer (IP-S) corrector plate, while effective, degrades quickly under the high-intensity beams typical of Undulator or X-ray Free-Electron Laser (XFEL) sources.
- Critical Need: The research explicitly calls for a robust material to deploy rotationally invariant/variant corrector plates at diffraction-limited storage rings and XFELs.
- 6CCVD Value Proposition: MPCVD Diamond (SCD/PCD) offers superior radiation hardness, thermal stability, and the required low-Z composition, making it the ideal material to replicate and extend this high-precision X-ray optics correction technology into high-flux environments.
- Future Direction: The proposed rotationally variant corrector plates (required to correct non-spherical aberrations like astigmatism) necessitate advanced 2D fabrication techniques, a capability 6CCVD supports through high-precision polishing and laser processing of diamond.
Technical Specifications
Section titled âTechnical SpecificationsâData extracted from the analysis of Be CRLs and the IP-S polymer corrector plate.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Initial r.m.s. Wavefront Error (CRL1) | 14.4 | pm | Before correction (Eq. 2) |
| Corrected r.m.s. Wavefront Error (CRL1) | 2.4 | pm | After correction (Measured) |
| Wavefront Error Reduction Factor | 6 | N/A | Improvement achieved by corrector |
| X-ray Energy (E) | 15 | keV | Characterization setup |
| CRL1 Lens Count (N) | 98 | N/A | Be bi-concave parabolic lenses |
| CRL Radius of Curvature (RL) | 200 | ”m | At the apex |
| Corrector Plate Transmission | ~99 | % | Measured using PIPS diode |
| Required Thickness Difference ($\Delta t$) | 10 | ”m | To produce 2$\pi\delta t/\lambda$ phase advance |
| Corrected Vertical Focus Size (FWHM) | 0.9 | ”m | After correction |
| Corrected Horizontal Focus Size (FWHM) | 2.48 | ”m | After correction |
| Corrector Material Density (IP-S) | 1.2 | g cm-3 | Polymer used for 3D printing |
| Target r.m.s. Wavefront Error | < 0.07$\lambda$ | N/A | Goal for complete compensation |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized a combination of advanced X-ray optics, wavefront sensing, and additive manufacturing techniques:
- X-ray Source & Optics: Monochromatic beam generated by a Si(111) double-crystal monochromator, focused by Be Compound Refractive Lenses (CRLs).
- Wavefront Sensing: Knife-edge imaging technique adapted to measure full 2D rotationally variant wavefront errors by rotating the knife-edge at various polar angles (e.g., 45°, 90°, 180°, 270°).
- Aberration Quantification: Wavefront error maps were quantified using Zernike polynomial expansion (up to order n = 16) to diagnose specific aberrations (e.g., spherical aberration, astigmatism, coma).
- Corrector Design: The average wavefront error profile was converted into a required optical path length difference ($\Delta w = \delta t$), which dictates the thickness profile of the corrector plate.
- Corrector Fabrication: A rotationally invariant corrector plate was manufactured in IP-S polymer using two-photon polymerization (3D printing) with a femtosecond Ti-sapphire laser (800 nm, 50 fs).
- Correction & Evaluation: The corrector plate was placed upstream of the Be CRLs. Compensation was evaluated by minimizing the r.m.s. wavefront error through lateral stepping (5 ”m and 1 ”m steps) and measuring the resulting focus profiles.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research identifies a critical need for robust, radiation-hard materials to enable high-performance wavefront correction at next-generation synchrotron and XFEL facilities. 6CCVDâs MPCVD diamond materials are perfectly suited to meet these demanding specifications.
Applicable Materials for Robust Wavefront Correction
Section titled âApplicable Materials for Robust Wavefront CorrectionâThe polymer IP-S degrades rapidly under high flux. Diamond, with its low atomic number (Z=6), high thermal conductivity, and extreme radiation hardness, is the superior choice for X-ray refractive optics operating at high-intensity beamlines.
| Application Requirement | 6CCVD Material Recommendation | Key Capability Match |
|---|---|---|
| High-Flux/XFEL Robustness | Optical Grade Single Crystal Diamond (SCD) | SCD offers the highest purity and lowest absorption, crucial for maintaining high transmission (~99% achieved in the paper) while surviving high-power beams. |
| Large-Area Correctors | Optical Grade Polycrystalline Diamond (PCD) | If the required aperture exceeds standard SCD sizes, 6CCVD offers PCD plates up to 125mm diameter, suitable for inch-size optics. |
| Astigmatism Correction | Boron-Doped Diamond (BDD) | While not the primary material for the corrector plate itself, BDD can be utilized for integrated components (e.g., conductive alignment features or integrated detectors) due to its metallic properties. |
Customization Potential
Section titled âCustomization PotentialâThe paper proposes complex, rotationally variant corrector plates (Case 1 and Case 2, Figs. 8a, 8b) which require precise 2D thickness profiling. 6CCVD offers the necessary fabrication and finishing services to realize these complex diamond optics.
- Custom Dimensions: 6CCVD can supply SCD plates up to 500 ”m thick, or PCD substrates up to 10mm thick, cut to custom dimensions required for specific CRL apertures (e.g., the $\pm$186 ”m and $\pm$305 ”m radii used in the study).
- Ultra-Precision Polishing: Achieving the required thickness profile for wavefront correction demands exceptional surface quality. 6CCVD guarantees:
- SCD Polishing: Surface roughness Ra < 1 nm.
- PCD Polishing: Surface roughness Ra < 5 nm (for inch-size wafers).
- Metalization Services: Although the corrector plate itself is dielectric, 6CCVD offers in-house metalization (Au, Pt, Pd, Ti, W, Cu) for integrating alignment marks, electrodes, or contact layers onto the diamond substrate, crucial for precise alignment of the corrector to the CRL optical axis.
- Laser Cutting and Shaping: We provide high-precision laser cutting services to achieve the exact external geometry and internal features required for mounting and alignment of the diamond corrector plate.
Engineering Support
Section titled âEngineering SupportâThe transition from polymer to diamond for X-ray refractive optics requires specialized expertise in material selection, doping, and surface finishing.
- 6CCVDâs in-house PhD team specializes in MPCVD diamond growth and processing for X-ray applications. We can assist researchers in determining the optimal diamond grade (SCD vs. PCD) and thickness required to achieve the necessary refractive decrement ($\delta$) and phase advance ($\Delta w$) for similar X-ray Wavefront Correction projects.
- We provide consultation on minimizing absorption ($\beta$) while maximizing refraction ($\delta$) for diamond optics, ensuring the highest possible transmission and performance in high-flux environments.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
A refractive phase corrector optics is proposed for the compensation of fabrication error of X-ray optical elements. Here, at-wavelength wavefront measurements of the focused X-ray beam by knife-edge imaging technique, the design of a three-dimensional corrector plate, its fabrication by 3D printing, and use of a corrector to compensate for X-ray lens figure errors are presented. A rotationally invariant corrector was manufactured in the polymer IP-S TM using additive manufacturing based on the two-photon polymerization technique. The fabricated corrector was characterized at the B16 Test beamline, Diamond Light Source, UK, showing a reduction in r.m.s. wavefront error of a Be compound refractive Lens (CRL) by a factor of six. The r.m.s. wavefront error is a figure of merit for the wavefront quality but, for X-ray lenses, with significant X-ray absorption, a form of the r.m.s. error with weighting proportional to the transmitted X-ray intensity has been proposed. The knife-edge imaging wavefront-sensing technique was adapted to measure rotationally variant wavefront errors from two different sets of Be CRL consisting of 98 and 24 lenses. The optical aberrations were then quantified using a Zernike polynomial expansion of the 2D wavefront error. The compensation by a rotationally invariant corrector plate was partial as the Be CRL wavefront error distribution was found to vary with polar angle indicating the presence of non-spherical aberration terms. A wavefront correction plate with rotationally anisotropic thickness is proposed to compensate for anisotropy in order to achieve good focusing by CRLs at beamlines operating at diffraction-limited storage rings.