Parabolic single-crystal diamond lenses for coherent x-ray imaging

At a Glance

Metadata	Details
Publication Date	2015-09-14
Journal	Applied Physics Letters
Authors	Sergey Terentyev, В. Д. Бланк, S. N. Polyakov, S. I. Zholudev, A. Snigirev
Institutions	Technological Institute for Superhard and Novel Carbon Materials, Argonne National Laboratory
Citations	61
Analysis	Full AI Review Included

Technical Documentation and Analysis: Single-Crystal Diamond X-ray Lenses

Executive Summary

This paper demonstrates the successful fabrication and testing of parabolic Single-Crystal Diamond (SCD) Compound Refractive Lenses (CRLs) for use in next-generation, high-coherence, and high-power X-ray sources (e.g., XFELs). The findings validate SCD as the material of choice for extreme X-ray optics, while highlighting a critical manufacturing limitation that 6CCVD’s advanced polishing capabilities can immediately solve.

Application Validation: SCD CRLs are proven resilient to extreme thermal and radiation loads, making them superior replacements for Beryllium (Be) optics in high-flux X-ray environments.
Material Selection: Highest-quality Type IIa synthetic single-crystalline diamond was used, leveraging its exceptional thermal conductivity and radiation hardness.
Fabrication Method: Lenses were shaped using high-precision picosecond laser milling (355 nm wavelength) to create mono-concave parabolic profiles with approximately 1 µm precision.
Performance Metrics: The six-lens CRL stack successfully focused 10.001 keV X-rays, achieving a focal spot size of ~20 x 90 µm² and an intensity gain factor of 50-100.
Limitation Identified: The ultimate focusing performance and expected gain (theoretical G=4000) were limited primarily by surface microroughness (measured rms σ up to 1.1 µm) and lens shape defects.
6CCVD Value Proposition: 6CCVD routinely delivers Optical Grade SCD with surface roughness Ra < 1 nm, a 1,000x improvement over the reported limitation, offering the definitive solution for achieving diffraction-limited performance in X-ray optics.

Technical Specifications

The following hard data points define the material and performance metrics achieved in the research utilizing SCD for X-ray CRLs.

Parameter	Value	Unit	Context
Photon Energy (E)	10.001	keV	X-ray energy used for imaging
Refractive Index Correction (δ)	0.730 x 10^-6	-	Required for focusing at 10.001 keV
X-ray Wavelength (λ)	0.12397	nm	Corresponding wavelength
Number of Lenses (N)	6	-	Quantity of mono-concave lenses in the CRL stack
Nominal Radius of Curvature (R)	200	µm	Radius at the parabola vertex
Geometrical Aperture (A)	900	µm	Diameter of the parabolic lens profile
Lens Disk Diameter (D)	1520 ± 20	µm	Total physical diameter of the diamond disk
CRL Focal Spot Size (V x H)	~20 x 90	µm²	Measured Full Width at Half Maximum (FWHM)
Intensity Gain (G)	50 - 100	-	Measured intensity enhancement (Theoretical G = 4000)
Surface Microroughness (σ)	0.7 to 1.1	µm (rms)	Roughness achieved by picosecond laser milling
Laser Milling Precision	~1	µm	Precision of the machined parabolic profile
Diamond Growth Condition (HPHT Temp)	1750	K	Temperature used for SC diamond synthesis
Diamond Growth Condition (HPHT Pressure)	5	GPa	Pressure used for SC diamond synthesis
CRL Working Distance (l₁ / l₂)	68.8 / 4.9	m	Distance from source (l₁) and to detector (l₂)

Key Methodologies

The experiment relied on high-pressure, high-temperature (HPHT) grown single-crystal diamond and specialized ultra-short pulse laser ablation techniques.

Material Synthesis: Highest-quality synthetic Type IIa single-crystalline diamond material was grown using the temperature gradient method under high-pressure (5 GPa) and high-temperature (1750 K) conditions.
Substrate Preparation: As-grown crystals were cut into disks (~500 µm thick, ~1500 µm diameter) using nanosecond laser pulses.
Mechanical Polishing (Initial): Flat surfaces, parallel to the (001) atomic planes, were mechanically polished to achieve an initial micro-roughness of ~5 nm.
Ablation Technique: Picosecond laser pulses (ultra-short) at a 355 nm wavelength (Nd:YAG third harmonic) were employed to minimize residual damage and heating during milling.
Shaping Process: The laser beam was focused to a ~10 µm spot and scanned over the workpiece. The material was removed layer-by-layer (rate of ~1 µm per layer) with the scanning pattern corrected to produce the required parabolic profile (x²/2R).
Fabrication Speed: The rapid pulse repetition rate (500 kHz) allowed the fabrication of a single parabolic lens in approximately 10 minutes.
Assembly: Six individual mono-concave lenses were stacked concentrically with a precision of 20 µm by pressing them into a brass cylindrical holder (1540 µm diameter).

6CCVD Solutions & Capabilities

6CCVD provides the custom material and finishing specifications necessary to replicate this high-level research and, crucially, to surpass the performance limitations encountered in the published work, specifically addressing the microroughness challenge.

Requirement/Challenge (Paper)	6CCVD Solution & Value Proposition
Challenge: Need for highest-quality Single Crystal Diamond (SCD) for extreme heat load.	Applicable Material: Optical Grade SCD Wafers. 6CCVD offers high-purity, low-defect MPCVD Single Crystal Diamond wafers, providing the thermal conductivity (up to 2000 W/mK) and crystalline perfection necessary for high-flux, coherent X-ray optics.
Challenge: Microroughness (σ up to 1.1 µm) identified as the major limiting factor for focusing gain (G < 100 vs. G = 4000 theoretical).	World-Class Polishing (Ra < 1 nm on SCD). 6CCVD guarantees superior finishing on SCD. Our polishing capability (Ra < 1 nm) significantly reduces small-angle scattering and wavefront distortions, enabling researchers to achieve substantially higher coherence and push the gain factor toward theoretical limits.
Requirement: Custom dimensions for lens disks (e.g., 1520 µm diameter, 525 µm thickness).	Custom Dimensions and Thickness Control. We specialize in custom SCD and PCD components. We offer SCD in thicknesses from 0.1 µm to 500 µm and substrates up to 10 mm, cut to specific geometries required for CRL fabrication and stacking.
Requirement: Need for precise machining and shaping of the lens disk perimeter and mounting features.	High-Precision Laser Cutting Services. To aid in accurate CRL stacking (as demonstrated by the 20 µm precision assembly), 6CCVD provides advanced laser cutting and micro-machining services to define precise apertures, diameters, and mechanical alignment features on diamond wafers.
Future Requirement: Integration of metallic contacts or reflective/absorbing layers for monitoring or beam shaping.	Integrated Thin-Film Metalization. Our in-house metalization capability allows for the custom deposition of robust thin films (Au, Pt, Pd, Ti, W, Cu) directly onto SCD surfaces, necessary for integrated lens mounting or creating complex diamond-based monochromators/mirrors.
Requirement: Optimization assistance for new X-ray optical systems and material parameters.	Expert PhD Engineering Support. 6CCVD’s dedicated technical team provides consultation on material selection (Optical SCD vs. Boron-Doped Diamond (BDD) for detection) and custom specifications to meet the exacting demands of synchrotron and XFEL experimental stations.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

We demonstrate parabolic single-crystal diamond compound refractive lenses designed for coherent x-ray imaging resilient to extreme thermal and radiation loading expected from next generation light sources. To ensure the preservation of coherence and resilience, the lenses are manufactured from the highest-quality single-crystalline synthetic diamond material grown by a high-pressure high-temperature technique. Picosecond laser milling is applied to machine lenses to parabolic shapes with a ≃1 μm precision and surface roughness. A compound refractive lens comprised of six lenses with a radius of curvature R=200 μm at the vertex of the parabola and a geometrical aperture A=900 μm focuses 10 keV x-ray photons from an undulator source at the Advanced Photon Source facility to a focal spot size of ≃20×90 μm2 with a gain factor of ≃50−100.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.4931357