Laser heating system at the Extreme Conditions Beamline, P02.2, PETRA III

At a Glance

Metadata	Details
Publication Date	2021-10-07
Journal	Journal of Synchrotron Radiation
Authors	Zuzana Konôpková, W. Morgenroth, Rachel J. Husband, Nico Giordano, Anna Pakhomova
Institutions	Deutsches Elektronen-Synchrotron DESY, European X-Ray Free-Electron Laser
Citations	24
Analysis	Full AI Review Included

Technical Documentation & Analysis: Laser Heating Systems for Extreme Conditions

Executive Summary

This documentation analyzes the research detailing the advanced laser heating system at the PETRA III Extreme Conditions Beamline (ECB), focusing on the critical role of high-quality diamond materials in achieving megabar pressures and accurate temperature measurements.

High-Pressure Capability: The system successfully achieved pressures up to 2 Mbar (200 GPa) in Diamond Anvil Cells (DACs) to study the melting curve of iron (Fe).
Advanced Heating Techniques: Utilizes dual 1072 nm Ytterbium fiber lasers for both continuous-wave (CW) and advanced pulsed/single-shot heating (microsecond to millisecond duration) to minimize carbon contamination and thermal runaway effects.
Optical Precision: Ray-tracing simulations (ZEMAX) were essential for characterizing the spectroradiometry path, confirming that spherical aberrations (LSA), rather than chromatic aberrations, are the dominant optical limitation in the 640-850 nm pyrometry range.
Material Purity Requirement: The necessity of pulsed heating underscores the challenge of carbon diffusion from the diamond anvils, demanding ultra-high purity, low-absorption Single Crystal Diamond (SCD) for reliable HPHT data.
Dimensional Control: Axial temperature gradients (up to 400 K at 3000 K) are highly dependent on sample thickness (e.g., 7 µm vs. 2 µm Fe foil), requiring DAC anvils and samples with extremely tight dimensional tolerances.
6CCVD Value Proposition: 6CCVD provides the necessary Optical Grade SCD substrates and custom polishing (Ra < 1 nm) required to replicate and extend this high-precision HPHT research.

Technical Specifications

The following hard data points were extracted from the analysis of the ECB laser heating system and its performance in DAC experiments:

Parameter	Value	Unit	Context
Maximum Pressure Achieved	2	Mbar	Melting curve of Iron (Fe)
X-ray Penetration Requirement	~6	mm	Required diamond thickness for high-energy X-ray transmission
Primary Laser Wavelength (NIR)	1072 ± 10	nm	Ytterbium fiber lasers
Secondary Laser Wavelength (IR)	10.6	µm	CO₂ laser (for transparent samples)
Maximum Laser Power (On-Axis)	200	W	Continuous Wave (CW)
Minimum X-ray Focus Spot Size (KB)	1.5 x 1.5	µm	Kirkpatrick-Baez mirror system
Typical Laser Spot Size (FWHM)	20	µm	Off-axis system, Gaussian shape
Temperature Measurement Range	640-850	nm	Spectral radiometry window
Estimated Temperature Error	10	%	Due to gradients, optical changes, and signal-to-noise ratio
Longitudinal Spherical Aberration (LSA)	12	mm	For geoHEAT lens (NA = 0.16) in 640-850 nm range
Axial Temperature Gradient (7 µm Fe)	Up to 400	K	Measured across 7 µm thick sample at 3000 K surface temperature
Shortest Laser Pulse Duration	Few	µs	Used for high repetition rate heating

Key Methodologies

The experiment relies on highly controlled synthesis and measurement techniques enabled by the specialized synchrotron beamline setup:

High-Pressure Containment: Samples were encapsulated in Diamond Anvil Cells (DACs), requiring high-quality SCD anvils capable of withstanding pressures up to 200 GPa while maintaining optical transparency for laser heating and pyrometry.
Dual-Sided Laser Heating: Two independent 1072 nm Ytterbium fiber lasers were used in both on-axis (co-axial with X-ray) and off-axis (25° angle) configurations to minimize axial temperature gradients across the sample.
Pulsed and Single-Shot Heating: The system was modulated using a digital delay/pulse generator (DDG) to produce microsecond pulses (1 µs) at 10 kHz or single-shot pulses (200-500 ms). This technique was critical for minimizing carbon contamination from the diamond anvils and mitigating dynamic sample behavior.
Time-Resolved X-ray Diffraction (XRD): Fast, large-area detectors (PerkinElmer XRD 1621, Pilatus 1M) were synchronized with the laser pulses and X-ray shutter to collect diffraction data during the transient high-temperature state.
Spectroradiometric Pyrometry: Temperature was measured by collecting thermal emission light from both the upstream and downstream sides of the sample and fitting the spectra (640-850 nm) to Planck’s law.
Optical System Characterization: Ray-tracing software (ZEMAX) was employed to model the optical path, confirming the necessity of specialized achromatic lenses (geoHEAT-60-NIR) to compensate for significant longitudinal spherical aberrations (LSA).

6CCVD Solutions & Capabilities

This research highlights the stringent material and dimensional requirements necessary for state-of-the-art HPHT research. 6CCVD is uniquely positioned to supply the high-purity, precision-engineered diamond materials required to replicate and advance these experiments.

Applicable Materials

Research Requirement	6CCVD Material Solution	Technical Rationale
High Optical Transparency (NIR)	Optical Grade SCD (Type IIa)	Essential for minimizing absorption of the 1072 nm Ytterbium laser and ensuring accurate spectroradiometry in the 640-850 nm range. Ultra-low nitrogen content minimizes defects.
Contamination Mitigation	High-Purity SCD Substrates	The use of pulsed heating is necessary to minimize carbon diffusion from the anvils. 6CCVD SCD offers maximum purity, reducing the risk of sample contamination during extreme thermal cycling.
Electrical/Resistive Heating	Boron-Doped Diamond (BDD)	For extending research beyond laser heating (e.g., measuring electrical conductivity or using resistive heating techniques up to 5000 K), 6CCVD supplies custom BDD films and substrates.
Large Area DACs	Inch-Size PCD Wafers	While SCD is preferred for optical clarity, 6CCVD offers Polycrystalline Diamond (PCD) plates up to 125 mm for large-volume HPHT synthesis or specialized DAC designs.

Customization Potential

The success of this experiment hinges on precise control over material dimensions and surface quality, areas where 6CCVD excels:

Precision Thickness Control: The paper demonstrates that axial temperature gradients are highly sensitive to sample and anvil thickness. 6CCVD offers SCD and PCD plates with thickness control from 0.1 µm up to 500 µm, ensuring the tight dimensional tolerances required for minimizing thermal gradients.
Ultra-Smooth Polishing: High-quality optical measurements require pristine surfaces. 6CCVD guarantees Ra < 1 nm polishing for SCD and Ra < 5 nm for inch-size PCD, critical for reducing scattering and optical aberrations in the pyrometry path.
Custom Metalization: Although not the primary focus of this paper, 6CCVD offers in-house metalization services (Au, Pt, Pd, Ti, W, Cu). This capability is vital for future DAC experiments requiring integrated resistive heaters or electrical contacts on the diamond anvils.
Custom Dimensions: 6CCVD provides custom laser cutting and shaping of diamond plates to fit specialized DAC geometries, ensuring compatibility with complex beamline setups like the on-axis and off-axis configurations described at PETRA III.

Engineering Support

6CCVD’s in-house team of PhD material scientists specializes in optimizing diamond properties for extreme conditions. We offer consultation services to assist researchers in:

Material Selection: Choosing the optimal diamond grade (e.g., low-birefringence SCD vs. high-conductivity BDD) to meet the specific optical, thermal, and electrical demands of similar HPHT DAC X-ray Diffraction projects.
Thermal Management: Advising on material dimensions and surface preparation to minimize the axial temperature gradients observed in laser heating experiments.
Custom Integration: Designing and fabricating diamond components with specific metalization layers for advanced electrical or resistive heating applications.

Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We offer global shipping (DDU default, DDP available) to support international synchrotron facilities and research groups.

View Original Abstract

A laser heating system for samples confined in diamond anvil cells paired with in situ X-ray diffraction measurements at the Extreme Conditions Beamline of PETRA III is presented. The system features two independent laser configurations (on-axis and off-axis of the X-ray path) allowing for a broad range of experiments using different designs of diamond anvil cells. The power of the continuous laser source can be modulated for use in various pulsed laser heating or flash heating applications. An example of such an application is illustrated here on the melting curve of iron at megabar pressures. The optical path of the spectroradiometry measurements is simulated with ray-tracing methods in order to assess the level of present aberrations in the system and the results are compared with other systems, that are using simpler lens optics. Based on the ray-tracing the choice of the first achromatic lens and other aspects for accurate temperature measurements are evaluated.

Tech Support

Original Source

DOI: https://doi.org/10.1107/s1600577521009231