Comprehensive Thermal Analysis of Diamond in a High-Power Raman Cavity Based on FVM-FEM Coupled Method

At a Glance

Metadata	Details
Publication Date	2021-06-15
Journal	Nanomaterials
Authors	Zhenxu Bai, Zhanpeng Zhang, Kun Wang, Jia Gao, Zhendong Zhang
Institutions	Hebei University of Technology, Macquarie University
Citations	28
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Power Diamond Raman Lasers

Executive Summary

This technical analysis, based on the study of thermal effects in high-power diamond Raman cavities, confirms the superior performance of Single Crystal Diamond (SCD) for extreme laser applications.

Material Validation: Single Crystal Diamond (SCD) is confirmed as the optimal gain medium for kilowatt-level laser scaling due to its exceptional thermal conductivity (2200 W/(m·K)) and low thermal expansion coefficient (10^-6 K^-1).
Rapid Thermal Stability: The thermal constant time—the period required for the temperature gradient to reach 99% of its steady-state value—is extremely short, ranging from 45 µs to 62 µs depending on the beam radius.
High Repetition Rate Potential: This rapid thermal response enables high-repetition-rate quasi-continuous-wave (quasi-CW) operation up to 10 kHz without significant heat accumulation, a critical factor for industrial and defense applications.
Minimal Deformation: Even at maximum absorbed power (200 W, corresponding to >1 kW output), the maximum thermal-induced deformation of the diamond is minimal (2.456 µm).
Cavity Stability: The small thermal deformation can be easily compensated by minor adjustments to the resonator length, ensuring the Stokes beam maintains high quality and cavity stability is preserved.
Methodology: The results were derived using a robust FVM-FEM coupled numerical simulation, providing a theoretical foundation for the design and thermal management of high-power Diamond Raman Lasers (DRLs).

Technical Specifications

Data extracted from the research paper regarding the SCD material and operational parameters.

Parameter	Value	Unit	Context
Diamond Thermal Conductivity	2200	W/(m·K)	SCD material property at 298 K
Coefficient of Thermal Expansion	10^-6	K^-1	SCD material property
Diamond Size (L x W x T)	8 x 4 x 1.2	mm	Single Crystal Diamond used in simulation
Maximum Absorbed Power (P_abs)	200	W	Corresponds to >1 kW output power
Pump/Stokes Beam Radius (w_p/w_s)	40 to 100	µm	Variable parameter in simulation
Thermal Constant Time (w_s = 40 µm)	45	µs	Time to reach 99% steady-state temperature gradient
Thermal Constant Time (w_s = 100 µm)	62	µs	Time to reach 99% steady-state temperature gradient
Maximum Thermal Deformation (200 W)	2.456 ± 0.004	µm	Maximum displacement at kW-level operation
Thermal Lens Focal Length (f)	54.5	mm	Resulting thermal lensing effect from 2.5 µm deformation
Cooling Temperature	298 (25)	K (C)	Constant temperature maintained at heat sink interface

Key Methodologies

The thermal and mechanical analysis utilized a coupled numerical approach to accurately model the complex dynamics within the high-power diamond Raman cavity.

Physical Setup Modeling: The simulation replicated an external-cavity Diamond Raman Laser (DRL) using an 8 mm x 4 mm x 1.2 mm Single Crystal Diamond (SCD) placed in a near-concentric cavity (Radius of Curvature = 100 mm).
Heat Source Definition: Thermal energy generated by Raman conversion (absorption and quantum defect) was modeled as a spherical heat source (radius 40-100 µm) located at the center of the diamond. Maximum absorbed power was set at 200 W.
Thermal Simulation (FVM): Transient and steady-state heat transfer processes—including conduction in the diamond and copper sink, air natural convection, and thermal radiation—were solved using the Finite Volume Method (FVM) via ANSYS Fluent.
Thermo-Elasticity Simulation (FEM): The thermal deformation and stress distribution induced by the temperature gradient were solved using the Finite Element Method (FEM) via ANSYS Static Structural.
Coupling: The FVM and FEM models were coupled to provide a comprehensive solution for the thermal-fluid-mechanical interaction, utilizing a refined grid system (28,667,369 elements) and a small time step (∆τ = 1 µs).
Boundary Conditions: The bottom surface of the copper heat sink was maintained at a constant wall temperature of 298 K (25 °C) to simulate infinite cooling capacity.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-purity, precision-engineered diamond materials required to replicate and advance the high-power Raman laser research detailed in this paper.

Research Requirement	6CCVD Solution & Capability	Technical Advantage
High-Purity Single Crystal Diamond (SCD)	Optical Grade SCD: SCD plates grown via MPCVD with extremely low nitrogen content (Type IIa equivalent). Available in thicknesses from 0.1 µm to 500 µm.	Guarantees the intrinsic thermal conductivity (2200 W/(m·K)) necessary to achieve the observed rapid thermal constant times (45-62 µs) and minimize thermal lensing.
Custom Dimensions (8 mm x 4 mm x 1.2 mm)	Custom Dimensions & Substrates: 6CCVD offers custom SCD plates and substrates up to 10 mm thick. We provide precision laser cutting to match exact cavity requirements.	Enables precise replication of the simulated geometry or scaling to larger apertures (PCD up to 125 mm) for next-generation kW-level systems.
Ultra-Smooth Optical Surfaces	Precision Polishing: SCD surfaces polished to Ra < 1 nm. Inch-size PCD polished to Ra < 5 nm.	Minimizes scattering losses and surface absorption, crucial for maintaining high beam quality (M²) and maximizing efficiency in high-finesse Raman cavities.
Integrated Thermal Management	Custom Metalization Services: In-house deposition of thin films including Ti, Pt, Au, W, Pd, and Cu.	Facilitates high-quality, low-thermal-resistance bonding to copper heat sinks (as used in the simulation) or integration of advanced microchannel cooling systems, ensuring optimal thermal steady-state performance.
Advanced Material Options	Boron-Doped Diamond (BDD): Available for applications requiring electrical conductivity (e.g., electrodes, active cooling elements) alongside high thermal performance.	Extends research potential beyond passive thermal management into electro-optic or active cooling regimes.

Engineering Support

6CCVD’s in-house PhD team specializes in high-power optics and thermal management. We offer consultation on material selection, geometry optimization, and thermal interface design to ensure successful implementation of Diamond Raman Laser (DRL) projects operating in the thermal-affected regime. We manage global logistics, offering DDU (default) and DDP shipping options worldwide.

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

View Original Abstract

Despite their extremely high thermal conductivity and low thermal expansion coefficients, thermal effects in diamond are still observed in high-power diamond Raman lasers, which proposes a challenge to their power scaling. Here, the dynamics of temperature gradient and stress distribution in the diamond are numerically simulated under different pump conditions. With a pump radius of 100 μm and an absorption power of up to 200 W (corresponding to the output power in kilowatt level), the establishment period of thermal steady-state in a millimeter diamond is only 50 μs, with the overall thermal-induced deformation of the diamond being less than 2.5 μm. The relationship between the deformation of diamond and the stability of the Raman cavity is also studied. These results provide a method to better optimize the diamond Raman laser performance at output powers up to kilowatt-level.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano11061572

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