Laser heating system at the Extreme Conditions Beamline, P02.2, PETRA III
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-10-07 |
| Journal | Journal of Synchrotron Radiation |
| Authors | Zuzana KonĂŽpkovĂĄ, W. Morgenroth, Rachel J. Husband, Nico Giordano, Anna Pakhomova |
| Institutions | European X-Ray Free-Electron Laser, Goethe University Frankfurt |
| Citations | 24 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThe Extreme Conditions Beamline (ECB) at PETRA III has developed a highly flexible laser heating system for Diamond Anvil Cell (DAC) experiments, enabling advanced in situ X-ray diffraction studies under megabar pressures and extreme temperatures.
- Dual Laser Configuration: The system utilizes two continuous-wave (CW) 1072 nm Ytterbium fiber lasers (200 W on-axis, 100 W off-axis) to accommodate various DAC geometries and ensure double-sided heating, minimizing axial temperature gradients.
- Pulsed and Flash Heating: The CW laser source is modulated by a DDG, allowing for time-resolved measurements using microsecond-scale pulses (high repetition rate) or single-shot millisecond flash heating.
- Optics Optimization: Ray-tracing simulations (ZEMAX) were performed on the spectroradiometry path (geoHEAT objective) to quantify aberrations and validate the optical design.
- Dominant Aberration Identified: The analysis confirmed that Longitudinal Spherical Aberration (LSA) is the primary limiting factor, not chromatic aberration, in the high Numerical Aperture (NA = 0.16) system.
- High-Performance Pyrometry: The geoHEAT objective maintains high image quality across its full aperture, focusing 95% of energy into a 200 ”m radius, avoiding the light loss associated with aperture reduction required by simpler lens systems.
- Demonstrated Capability: The system successfully measured the melting curve of iron (Fe) up to 2 Mbar, utilizing single-shot heating to minimize sample contamination and reaction time.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| X-ray Beamline | P02.2 (ECB) | N/A | PETRA III Synchrotron |
| X-ray Operating Energies | 25.6, 42.7 | keV | Fixed energies for high penetration |
| KB Mirror Focus Spot Size | 1.5 x 1.5 | ”m | Minimum FWHM focus |
| CRL Focus Spot Size | 8 (H) x 2 (V) | ”m | Minimum FWHM focus |
| Heating Laser Type | Ytterbium Fiber | N/A | CW, 1072 nm |
| On-Axis Laser Power (Max) | 200 | W | Coupled co-axially with X-ray path |
| Off-Axis Laser Power (Max) | 100 | W | Angle of ~25° to X-ray path |
| Typical Laser Spot Size | 20 | ”m (FWHM) | Measured at best focus |
| Temperature Range (Heating) | 1000-10000 | K | General laser heating capability |
| Spectrometry Spectral Range | 640-850 | nm | Used for Planck fit temperature calculation |
| Objective Lens | geoHEAT-60-NIR | N/A | Optimized for visible (600-900 nm) and laser (1020-1100 nm) |
| Objective Numerical Aperture (NA) | 0.16 | N/A | Full 19 mm lens diameter |
| Longitudinal Spherical Aberration (LSA) | 12 | mm | Over 640-850 nm range (full aperture) |
| Chromatic Focal Shift | 12 | mm | Over 600-900 nm range |
| Axial Temperature Gradient (7 ”m Fe @ 3000 K) | 400 | K | FEM simulation result |
| Time-Resolved Heating Pulse Duration | Microseconds | N/A | Minimum pulse length achievable |
Key Methodologies
Section titled âKey MethodologiesâThe experimental methodology integrates high-brilliance X-ray diffraction with advanced laser heating and spectroradiometry, optimized through ray-tracing analysis.
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Laser Configuration and Control:
- Two independent 1072 nm Yb fiber lasers are used, split into upstream and downstream beams for double-sided heating.
- The on-axis laser is coupled via a dichroic mirror into the temperature measurement path using a specialized geoHEAT objective.
- The CW laser power is modulated using a DDG to execute pulsed heating (microsecond pulses at kHz rates) or single-shot flash heating (millisecond pulses).
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Optical Alignment and Visualization:
- A 5 ”m pinhole placed at the sample position is used to co-align the imaging camera and the spectrometer entrance slit.
- The X-ray beam position is aligned to the optical reference mark by visualizing X-ray induced fluorescence, ensuring temperature measurement occurs in the X-ray probed volume.
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Spectroradiometry and Temperature Calculation:
- Thermal radiation is collected from both sides of the DAC via the geoHEAT objective and guided to a Shamrock spectrometer equipped with an iStar ICCD (time-resolved) and an iDUS CCD (CW, high QE).
- The spectral range 640-850 nm is used for temperature fitting to Planckâs law.
- The systemâs optical transfer function (including aberrations and mirror reflectivity) is corrected using a calibrated tungsten halogen lamp reference source.
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Aberration Management (ZEMAX Analysis):
- Ray-tracing simulations confirmed that the geoHEAT objectiveâs performance is limited primarily by LSA (12 mm spread) rather than chromatic shift.
- The design allows the use of the full 19 mm aperture (NA = 0.16), maximizing collected light intensity without compromising temperature accuracy, unlike simpler achromats which require aperture stopping.
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Pulsed Heating and XRD Acquisition:
- For time-resolved studies (e.g., Fe melting), the DDG synchronizes the laser pulse, the iStar ICCD gate, and the X-ray detector (Pilatus 1M) exposure window.
- This synchronization allows monitoring of lattice expansion (XRD peak shift) and temperature profile along the duration of a single microsecond-scale laser pulse.
Commercial Applications
Section titled âCommercial ApplicationsâThe technologies and methodologies developed for the ECB laser heating system are critical for several high-tech and industrial sectors requiring material characterization under extreme conditions.
- Geophysics and Planetary Science:
- Accurate determination of melting curves and phase diagrams of core materials (e.g., Fe, silicates) up to multi-megabar pressures, essential for modeling planetary interiors and dynamics.
- Advanced Materials Synthesis:
- Synthesis and characterization of novel high-density materials, superhard phases, and high-temperature ceramics under controlled static P-T conditions.
- High-Performance Optics and Metrology:
- The rigorous ZEMAX ray-tracing and aberration analysis techniques used to optimize the geoHEAT objective are directly transferable to designing high-NA, multi-wavelength optical systems for advanced microscopy, lithography, and industrial inspection.
- Thermal Management and Energy Research:
- Measurement of transient thermal and electrical conductivities of materials using pulsed heating techniques, relevant for designing high-efficiency energy storage devices and high-power electronic components.
- Nuclear and Reactor Materials:
- Studying the stability and phase transitions of metals and alloys under rapid thermal cycling (flash heating), simulating extreme conditions encountered in nuclear reactor environments.
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.