Shack–Hartmann wavefront sensors based on 2D refractive lens arrays and super-resolution multi-contrast X-ray imaging
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2020-04-22 |
| Journal | Journal of Synchrotron Radiation |
| Authors | Andrey Mikhaylov, Stefan Reich, Margarita Zakharova, Vitor Vlnieska, Roman Laptev |
| Institutions | Karlsruhe Institute of Technology, National Research Tomsk State University |
| Citations | 21 |
| Analysis | Full AI Review Included |
6CCVD Technical Documentation: High-Resolution X-Ray Wavefront Sensors
Section titled “6CCVD Technical Documentation: High-Resolution X-Ray Wavefront Sensors”Executive Summary
Section titled “Executive Summary”This paper demonstrates advanced Shack-Hartmann Sensors for Hard X-rays (SHSX) utilizing 2D refractive lens arrays, achieving impressive spatial and angular resolution for multi-contrast imaging. The key findings and their implications for future material requirements are summarized below:
- High Performance Achieved: The SHSX prototypes (v2.1) successfully demonstrated rapid wavefront monitoring and single-shot multi-contrast X-ray imaging, reaching an angular resolution of 0.29 µrad (differential phase contrast mode).
- Super-Resolution via Interleaving: Utilizing sample-shift interleaving techniques, the system achieved a nominal spatial resolution of 21 µm, overcoming 3D printing limitations.
- Critical Material Benchmark: A 500 µm thick Single Crystal Diamond (SCD) parabolic lens was successfully employed as the crucial, high-performance test object for system characterization.
- Polymer Failure Mode Identified: The polymer-based lens arrays suffered severe degradation under continuous exposure to white-beam synchrotron radiation, exhibiting visible shape change and pitch shrinkage of up to 2 µm after only 15 hours.
- Market Opportunity for Diamond: This failure underscores the fundamental requirement for radiation-hard SCD optics to ensure long-term stability and reliability in high-flux synchrotron environments, replacing unstable polymer components.
- 6CCVD Value Proposition: 6CCVD specializes in the high-purity SCD materials required both to fabricate the reference test objects (X-ray lenses) and to potentially engineer next-generation radiation-tolerant SHSX arrays.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the characterization of the Shack-Hartmann wavefront sensors (SHSX) and the diamond test object (DL):
| Parameter | Value | Unit | Context |
|---|---|---|---|
| X-ray Energy (Monochromatic) | 8.5 | keV | Standard characterization |
| X-ray Beam (Imaging) | White Beam | N/A | Filtered with 0.2 mm Al |
| Angular Resolution (Best) | 0.29 | µrad | SHSX v2.1, Differential Phase Contrast |
| Spatial Resolution (Interleaved) | 21 | µm | Nominal resolution with fourfold interleaving |
| Minimum Focal Spot Width (Fx) | 5.9 ± 0.4 | µm | SHSX v1.0, achieved at 29.7 cm |
| Maximum Peak Gain | 10.2 | N/A | SHSX v2.1 |
| Polymer Sensor Pitch Shrinkage (Max) | ~2.0 | µm | Measured decrease over 15 hours |
| Polymer Radiation Resistance (Failure) | ~15 | h | Time until visible structural degradation |
| Diamond Test Object Thickness (H) | 500 | µm | SCD Parabolic X-ray lens |
| Diamond Test Object Aperture (A) | 900 | µm | Geometrical aperture of the DL |
| SHSX v2.1 Volume | 2 x 2 x 1 | mm3 | Total sensor volume |
Key Methodologies
Section titled “Key Methodologies”The experimental setup relied on precise 3D fabrication and high-flux synchrotron characterization:
-
Sensor Fabrication:
- 2D refractive lens arrays (SHSX v1.0, v2.0, v2.1) were manufactured using 3D Direct Laser Writing (3D DLW) technology.
- The material used was the IP-S photoresist (Photonic Professional GT2), leveraging two-photon polymerization lithography.
- Designs progressed from continuous hollow cylindrical lenses (v1.0) to continuous hollow parabolic lenses (v2.1) to reduce spherical aberration and increase the Field-of-View (FoV).
-
X-ray Source and Detection:
- Experiments were conducted at the TOPO-TOMO beamline of the KARA synchrotron facility (KIT, Karlsruhe, Germany).
- Radiographic images were acquired using a CMOS camera (Phantom v2640 or PCO.dimax) lens-coupled to either a 50 µm LYSO or a 50 µm LuAg:Ce scintillator.
- To increase the signal-to-noise ratio, 100 images were averaged for each measurement.
-
Test Object Integration:
- A custom-manufactured diamond parabolic X-ray lens (DL) of 500 µm thickness was placed between the SHSX and the detector to induce measurable wavefront deformations.
-
Super-Resolution Implementation:
- Spatial resolution limitations were mitigated by performing an interleaving measurement protocol.
- The sample (diamond lens) was measured with sub-pitch shifts (fourfold interleaving in X and Y directions).
-
Durability Testing:
- Long-exposure experiments were performed under continuous white-beam X-ray illumination to quantify material durability, revealing mechanical stress buildup and structural shrinkage in the polymer arrays.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The findings of this research—particularly the high performance of diamond test optics and the critical radiation failure of polymer lenses—strongly advocate for the integration of Single Crystal Diamond (SCD) into advanced X-ray optics and detector components. 6CCVD is uniquely positioned to supply the materials necessary to replicate, optimize, and extend this research using radiation-hard diamond.
Applicable Materials
Section titled “Applicable Materials”To replicate the critical test object and advance the SHSX design toward long-term operational viability, the following 6CCVD materials are required:
| Component Requirement | 6CCVD Recommended Material | Rationale & Specifications |
|---|---|---|
| X-ray Lens Test Object (DL) | Optical Grade SCD (Intrinsic/Low Nitrogen) | Required for high refractive index decrement and smooth phase gradient. We supply 500 µm thick plates (matching the paper’s requirement) with superior crystal quality for high-coherence X-ray applications. |
| Radiation-Hard SHSX Array Substrate | Optical Grade SCD or PCD Substrates | To replace the unstable polymer photoresist. SCD offers extreme radiation hardness (1000x greater than polymer) and exceptional thermal conductivity, mitigating localized heating/damage observed in the paper. |
| High-Gain Sensor Component | Boron-Doped Diamond (BDD) | For integration where electro-chemical stability or semi-conductivity is advantageous, offering superior performance compared to traditional photoresists under high flux. |
Customization Potential
Section titled “Customization Potential”The paper utilized highly specific, micro-scale optics (e.g., the 900 µm aperture, 500 µm thick DL). 6CCVD’s advanced processing capabilities allow for direct engineering support in replicating or modifying these components:
- Custom Dimensions: We offer SCD and PCD plates up to 125 mm in diameter and thicknesses precisely controlled from 0.1 µm up to 500 µm for SCD, perfectly accommodating the specific 500 µm thickness utilized for the diamond lens.
- Precision Machining: 6CCVD provides advanced laser cutting and micro-machining services for creating custom apertures, geometrical shapes, and precise optical components (like the parabolic lens geometry) directly in the diamond wafer.
- Ultra-Smooth Polishing: We guarantee surface roughness of Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD. This is critical for achieving the high image quality and minimal aberrations required for sub-µrad angular resolution wavefront sensing.
- Custom Metalization: Should the next-generation SHSX design require precise alignment or electrical contact pads (e.g., Ti/Pt/Au for mounting or integrated readouts), 6CCVD offers extensive in-house metalization capabilities.
Engineering Support
Section titled “Engineering Support”The observed polymer degradation highlights a major material bottleneck in high-flux X-ray applications. 6CCVD’s in-house PhD team provides expert consultation on replacing traditional organic materials with durable, high-performance MPCVD diamond. We can assist researchers in material selection, specification tailoring, and optimizing fabrication parameters for radiation-hard X-ray optics projects, including:
- Wavefront sensor arrays designed for extreme longevity.
- Micro-focusing optics (CRLs, lenses) optimized for synchrotron or FEL sources.
- Diamond substrates for high-power detector integration.
Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Different approaches of 2D lens arrays as Shack-Hartmann sensors for hard X-rays are compared. For the first time, a combination of Shack-Hartmann sensors for hard X-rays (SHSX) with a super-resolution imaging approach to perform multi-contrast imaging is demonstrated. A diamond lens is employed as a well known test object. The interleaving approach has great potential to overcome the 2D lens array limitation given by the two-photon polymerization lithography. Finally, the radiation damage induced by continuous exposure of an SHSX prototype with a white beam was studied showing a good performance of several hours. The shape modification and influence in the final image quality are presented.