Combined laser ultrasonics, laser heating, and Raman scattering in diamond anvil cell system

At a Glance

Metadata	Details
Publication Date	2016-12-01
Journal	Review of Scientific Instruments
Authors	Pavel V. Zinin, Vitali B. Prakapenka, Katherine Burgess, Shoko Odake, Nikolay Chigarev
Institutions	Centre National de la Recherche Scientifique, Federal State Budgetary Institution of Science “Scientific and Technological Center of Unique Instrumentation” of the Russian Academy of Sciences
Citations	23
Analysis	Full AI Review Included

6CCVD Technical Documentation: Analysis of HPHT Laser Ultrasonics in Diamond Anvil Cells

Executive Summary

This document analyzes the research detailing a combined Laser Ultrasonics (LU), Laser Heating (LH), and Raman Scattering system within a Diamond Anvil Cell (DAC). This multi-functional platform provides unprecedented capability for in situ measurement of elastic properties of non-transparent materials under High Pressure and High Temperature (HPHT) conditions.

Integrated HPHT Platform: A unique LU-LH-DAC system was successfully developed, integrating three distinct measurement techniques into a single, remotely controlled platform for extreme conditions research.
Record Conditions Achieved: The system demonstrated the direct measurement of skimming acoustical wave velocities in iron samples at a record high temperature of 2580 K and pressures up to 22 GPa.
Direct Elastic Property Measurement: The technique allows for the direct determination of longitudinal (L) and shear (T) wave velocities in materials like iron, critical for geophysical modeling of the Earth’s core.
Enabling Material: Single Crystal Diamond (SCD) is the indispensable enabling material, providing the necessary mechanical strength (22 GPa) and optical transparency (532 nm and 1064 nm) for the multiple laser systems.
Precision and Accuracy: Velocity measurements rely heavily on accurate determination of the DAC diamond geometry (thickness, index of refraction, $n\approx 2.42$) and require the development of layered acoustic pulse propagation theory to achieve sub-percent accuracy goals (0.1%-0.01%).
Sales Driver: Replicating or extending this demanding research requires ultra-high purity, high-optical-grade SCD anvils with custom dimensions and superior polishing, a core competency of 6CCVD.

Technical Specifications

The following table extracts critical hard data and operational parameters demonstrated or utilized in the LU-LH-DAC system.

Parameter	Value	Unit	Context
Peak Pressure Achieved	22.1	GPa	In situ measurement of elastic properties in iron
Peak Temperature Achieved	2580	K	Record high for LU-DAC system
Heating Laser Wavelength	1064	nm	Fiber laser, precise power control (2 to 100 W)
Pump Laser Wavelength (Excitation)	1064	nm	Nano-pulse laser (0.5 ns pulse width)
Probe Laser Wavelength (Detection)	532	nm	Continuous Wave (CW) laser
Heating Spot Size Control Range	8 to 100	µm	Achieved using π-shaper
Measured Skimming L-Velocity (SL_Fe)	6.85 ± 0.1	km/s	Iron at 22.1 GPa
Measured Bulk L-Velocity (L)	6.78 ± 0.07	km/s	Iron at 22.1 GPa (LL peak fitting)
Diamond Refractive Index (n)	2.42	Unitless	Used for calculating laser focus depth corrections
Required Accuracy Goal	0.1% to 0.01%	Percent	Target accuracy for future acoustical velocity improvements

Key Methodologies

The experiment utilized a complex, multi-component setup, focusing on synergistic measurements under extreme HPHT conditions within a DAC.

System Integration: The core LU-LH-DAC platform combined four main components: (1) Laser Ultrasonics (LU) system, (2) Laser Heating (LH) system (1064 nm fiber laser with 2-100 W range), (3) Spectrometer for Raman scattering (pressure) and black body radiation fit (temperature), and (4) High-magnification double-sided optical imaging.
Acoustical Excitation and Detection: Acoustic waves were generated using a 0.5 ns, 1064 nm pump laser pulse via thermoelastic expansion. The resulting acoustic signals (including skimming waves, bulk L and T waves, and mode conversions) were detected using a 532 nm CW probe laser in a photoacoustic configuration (reflection or transmission mode).
Point-Source-Point-Receiver Configuration: The LU technique was executed in a point-source-point-receiver configuration, allowing researchers to determine specimen thickness and wave velocity by varying the distance ($d$) between the pump and probe spots.
Temperature Management (LH): A 1064 nm fiber laser, utilizing a specialized π-shaper, controlled the heating spot size (8 µm to 100 µm) and shape. Temperature was monitored remotely using spectroscopic measurements (black body radiation fit via Planck’s law).
Pressure Management (Raman): Pressure was monitored in situ using the fluorescence spectrum of ruby or the Raman G band signal of the SCD diamond at the specimen/diamond interface.
Data Analysis & Correction: Acoustic velocities were derived from the linear fit of propagation time ($\tau$) versus generator-detector distance ($d$). Crucially, measurements required geometric correction factors related to the high refractive index ($n \approx 2.42$) of the diamond anvils to accurately determine focal spot locations inside the high-pressure chamber (Eq. 5).

6CCVD Solutions & Capabilities

The successful execution of high-frequency acoustic experiments at multi-GPa and multi-thousand Kelvin conditions hinges entirely on the quality and mechanical robustness of the SCD diamond anvils. 6CCVD delivers the specialized material and processing required to meet these extreme demands.

Applicable Materials

To replicate and extend this research, particularly focusing on optimizing signal transmission at 532 nm and 1064 nm, and ensuring mechanical integrity at 22 GPa and above, researchers require the highest quality MPCVD material:

Optical Grade Single Crystal Diamond (SCD): Essential for use as DAC anvils. SCD provides the requisite ultimate strength (preventing fracture at >22 GPa) and superior optical transparency across the visible (532 nm probe) and near-IR (1064 nm pump/heating) wavelengths, ensuring minimal beam distortion and absorption heating. 6CCVD specializes in high-purity, low-birefringence SCD required for demanding spectroscopic and ultrasonic applications.
High-Purity Polycrystalline Diamond (PCD): While SCD is preferred for maximal transparency, PCD plates up to 125mm can serve as robust backing substrates or windows in systems requiring high mechanical stability but where minimal light scattering is a less critical factor than size/cost.

Customization Potential

The experimental findings emphasize the need for highly precise material preparation, especially regarding dimensions, surface finish, and potential incorporation of thin-film transducers.

Requirement from Paper	6CCVD Custom Capability	Application Benefit
High Refractive Index Correction (n=2.42)	Custom SCD Thickness and Parallelism	We provide custom SCD substrates up to 10mm thickness, manufactured with exceptional parallelism crucial for reducing error in DAC displacement calculations (Eq. 5).
Acoustical Transducer Layer	Internal Metalization Services (Au, Pt, Ti)	The paper suggests using a thin layer of iron or Pt/Rh alloy as a transducer. 6CCVD offers custom metalization (including Ti/Pt/Au contact layers) directly onto SCD surfaces, creating precise thin-film transducers for opto-acoustic excitation.
Superior Optical Detection	SCD Polishing (Ra < 1nm)	Achieving high accuracy (target 0.01%) depends on stable probe reflection. Our ultra-low roughness SCD polishing (Ra < 1nm) minimizes scattering and maximizes reflectivity stability during dynamic HPHT measurements.
Complex Geometric Shaping	Custom Laser Cutting	For custom DAC geometries or specialized probe access windows, 6CCVD offers precision laser cutting and shaping services tailored to complex experimental requirements.

Engineering Support

The challenges in LU-LH-DAC research involve complex physics, acoustic pulse propagation theory in layered materials, and extreme temperature/pressure management. 6CCVD’s in-house PhD team can assist researchers in material selection, specification optimization, and geometric design for similar high-pressure geoscience, refractory material science, or phase transition projects, ensuring the SCD material supports the rigorous demands of integrated laser systems.

Call to Action

To drive further accuracy improvements and push the boundaries of HPHT experimentation, the SCD components must be meticulously engineered. For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

We developed a multi-functional in situ measurement system under high pressure equipped with a laser ultrasonics (LU) system, Raman device, and laser heating system (LU-LH) in a diamond anvil cell (DAC). The system consists of four components: (1) a LU-DAC system (probe and pump lasers, photodetector, and oscilloscope) and DAC; (2) a fiber laser, which is designed to allow precise control of the total power in the range from 2 to 100 W by changing the diode current, for heating samples; (3) a spectrometer for measuring the temperature of the sample (using black body radiation), fluorescence spectrum (spectrum of the ruby for pressure measurement), and Raman scattering measurements inside a DAC under high pressure and high temperature (HPHT) conditions; and (4) an optical system to focus laser beams on the sample and image it in the DAC. The system is unique and allows us to do the following: (a) measure the shear and longitudinal velocities of non-transparent materials under HPHT; (b) measure temperature in a DAC under HPHT conditions using Planck’s law; (c) measure pressure in a DAC using a Raman signal; and (d) measure acoustical properties of small flat specimens removed from the DAC after HPHT treatment. In this report, we demonstrate that the LU-LH-DAC system allows measurements of velocities of the skimming waves in iron at 2580 K and 22 GPa.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.4972588

References

1989 - Theory of the Earth
2005 - Advances in High-Pressure Techniques for Geophysical Applications
2005 - Advances in High-Pressure Techniques for Geophysical Applications [Crossref]
2005 - Advances in High-Pressure Techniques for Geophysical Applications