Numerical Simulation of Long-Wave Infrared Generation Using an External Cavity Diamond Raman Laser

At a Glance

Metadata	Details
Publication Date	2021-07-05
Journal	Frontiers in Physics
Authors	Hui Chen, Zhenxu Bai, Zhao Chen, Xuezong Yang, Jie Ding
Institutions	Hebei University of Technology, Macquarie University
Citations	4
Analysis	Full AI Review Included

Technical Documentation & Analysis: Long-Wave Infrared Diamond Raman Lasers

This document analyzes the research paper “Numerical Simulation of Long-Wave Infrared Generation Using an External Cavity Diamond Raman Laser” to provide technical specifications and demonstrate how 6CCVD’s advanced MPCVD diamond materials and customization services are essential for replicating and advancing this high-power LWIR technology.

Executive Summary

The research validates the potential of Single Crystal Diamond (SCD) for generating high-power Long-Wave Infrared (LWIR) radiation via Stimulated Raman Scattering (SRS). Key findings and the core value proposition are summarized below:

LWIR Generation: A numerical model confirms that an external cavity Diamond Raman Laser (DRL), pumped at 4.3 µm (MWIR), can efficiently generate 10 µm LWIR output, overcoming limitations of traditional QCLs and OPOs.
Material Advantage: The feasibility relies entirely on the exceptional properties of MPCVD SCD, specifically its broad spectral transmission (>0.2 µm to >50 µm), highest known Raman frequency shift (1,332 cm⁻¹), and extreme thermal conductivity (>2000 W m⁻¹ K⁻¹).
High Power Potential: Simulations predict that a 1 cm³ SCD crystal can generate maximum Stokes peak power approaching 123 MW (at 40% output coupling), establishing diamond as a viable platform for high-power LWIR systems.
Conversion Efficiency: Optimal cavity design parameters (crystal length, pump waist, and output coupling) were determined, achieving a simulated maximum conversion efficiency approaching the quantum limit of ~43%.
Geometry Requirement: The use of a Brewster-cut SCD crystal (~67.2°) is critical for high-power operation, avoiding the absorption loss and damage threshold limitations associated with traditional thin-film coatings in the LWIR band.
6CCVD Positioning: 6CCVD specializes in the high-purity, low-loss SCD required for this application, offering custom dimensions, precise Brewster cuts, and ultra-low absorption properties necessary for high-gain LWIR conversion.

Technical Specifications

The following hard data points were extracted from the simulation and material analysis:

Parameter	Value	Unit	Context
Pump Wavelength	4.3	µm	MWIR Input
Stokes Wavelength	10	µm	LWIR Output (First-order Stokes)
Raman Frequency Shift (SCD)	1,332.3	cm⁻¹	Largest among known Raman crystals
Thermal Conductivity (SCD)	>2000	W m⁻¹ K⁻¹	Critical for stable, high-power operation
Crystal Length (Simulated)	5	mm	Initial length used in model
Optimal Crystal Length (L_opt)	~10	mm	Varies based on pump power
Brewster Cut Angle	~67.2	°	Used to avoid crystal coatings
Absorption Coefficient (α)	0.03	cm⁻¹	Used in steady-state model
Raman Generation Threshold (P_thr)	34.8	kW	Calculated at T = 0.5% output coupling
Maximum Conversion Efficiency	~43	%	Approaching the quantum limit
Predicted Max Stokes Peak Power	123	MW	For 1x1x1 cm³ SCD, T=40%
SCD Refractive Index (n)	2.38	N/A	Constant for wavelengths >2 µm

Key Methodologies

The numerical simulation utilized a steady-state model of an external cavity DRL to optimize output characteristics based on critical resonator and pump parameters.

Cavity Design: An external-cavity DRL setup was modeled using a near-concentric cavity structure with a total length of 102 mm. Input and output couplers had a curvature radius of 50 mm.
Pump Source: A 4.3 µm MWIR laser was simulated as the pump source. A focusing lens (F3, f=100 mm) was used to achieve optimal mode matching, focusing the pump beam to a waist size of 252 µm at the center of the diamond.
Raman Medium: A single-crystal diamond (SCD) of 5 mm length was placed at the Stokes beam waist. The crystal was specified as Brewster-cut (~67.2°) to eliminate the need for anti-reflection coatings, thereby avoiding film damage and absorption loss.
Coating Specification: The input coupler was modeled as Anti-Reflection (AR) coated at 4.3 µm and High-Reflection (HR) coated at 10 µm. The output coupler was HR coated at 4.3 µm.
Parameter Optimization: The steady-state model was used to analyze the relationships between output power and three key variables: output coupler transmission (T), pump waist size (W_p), and crystal length (L). Optimal values for these parameters were determined to maximize 10 µm Stokes output.

6CCVD Solutions & Capabilities

The successful realization of a high-power LWIR DRL hinges on the availability of high-quality, low-absorption, custom-fabricated diamond. 6CCVD is uniquely positioned to supply the necessary materials and engineering expertise to meet or exceed the requirements of this research.

Applicable Materials

To replicate and extend this research, the highest quality Single Crystal Diamond (SCD) is required, specifically optimized for low absorption in the LWIR band (>8 µm).

Optical Grade SCD: 6CCVD provides high-purity, low-nitrogen SCD plates, essential for minimizing absorption losses (α = 0.03 cm⁻¹ used in the simulation) that limit LWIR conversion efficiency. Our SCD material ensures the high thermal conductivity (>2000 W m⁻¹ K⁻¹) necessary to manage thermal load under MW-level peak power operation.
Custom Thickness: While the simulation used 5 mm and optimized for ~10 mm, 6CCVD can supply SCD substrates up to 500 µm thick, and substrates up to 10 mm thick, allowing researchers to test various interaction lengths (L) as analyzed in Figure 3F.

Customization Potential

The paper highlights the necessity of precise geometry (Brewster cut) and specific dimensions for optimal cavity performance. 6CCVD’s advanced fabrication capabilities directly address these needs:

Requirement from Paper	6CCVD Capability	Technical Advantage
Brewster Cut Geometry	Precision Laser Cutting & Polishing	We provide custom angular cuts (e.g., 67.2°) and geometries, ensuring the crystal interfaces are perfectly aligned to avoid coatings and minimize Fresnel losses.
Custom Dimensions	Plates/Wafers up to 125 mm	We can supply SCD plates up to 10 mm thick and large-area PCD up to 125 mm, enabling scaling toward the 1 cm³ volume predicted for 123 MW output.
Surface Quality	Ultra-Precision Polishing	SCD polishing to Ra < 1 nm is standard, minimizing scattering losses which are critical in long-cavity, high-finesse DRL systems.
Metalization (General)	Internal Metalization Services	Although the crystal was uncoated in this study, 6CCVD offers custom metalization (Au, Pt, Pd, Ti, W, Cu) for cavity mirrors, heat sinks, or integrated components required for advanced DRL designs.

Engineering Support

The optimization of DRL systems requires balancing material properties (gain coefficient, absorption) with resonator parameters (waist size, crystal length).

LWIR Material Consultation: 6CCVD’s in-house PhD team specializes in diamond optics and high-power laser applications. We offer expert consultation on material selection, purity requirements, and geometry optimization for similar LWIR Raman Laser projects.
Thermal Management: Given the high thermal load predicted for MW-level operation, our team can assist in designing diamond heat spreaders or mounting solutions utilizing diamond’s superior thermal properties to ensure stable, continuous operation.

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

View Original Abstract

Diamond has a broad spectral transmission range (&gt;0.2 μm) and the largest Raman frequency shift (1,332 cm −1 ) among known Raman crystals. Hence, the diamond Raman laser has the potential to achieve lasing in the long-wave infrared (LWIR) range, which is difficult to reach via other crystalline lasers. Here, we report a new approach to achieve LWIR output using diamond Raman conversion and provide the corresponding analysis model and simulation results. The conversion efficiency is analyzed as function of the pump waist size, output-coupler transmission, and crystal length, at constant pump power. The maximum output power at which a diamond of relatively large size can be operated without damage is predicted. This study paves a way for high-power LWIR lasing in diamond.

Tech Support

Original Source

DOI: https://doi.org/10.3389/fphy.2021.671559

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