Numerical optimization of the extra-cavity diamond Raman laser in the multi-phonon absorption band

At a Glance

Metadata	Details
Publication Date	2022-10-12
Journal	Frontiers in Physics
Authors	Zhenhua Shao, Bei Li, Hongzhi Chen, Jun Cao
Institutions	Shanghai Power Equipment Research Institute
Analysis	Full AI Review Included

Technical Documentation & Analysis: Mid-Infrared Diamond Raman Lasers

6CCVD Analysis of “Numerical optimization of the extra-cavity diamond Raman laser in the multi-phonon absorption band”

Executive Summary

This research provides critical numerical modeling for optimizing extra-cavity diamond Raman lasers operating in the challenging mid-infrared (MIR) multi-phonon absorption band (2.5-3 µm). The findings directly inform the material specifications required for high-efficiency nonlinear frequency conversion.

Application Focus: Optimization of Stimulated Raman Scattering (SRS) in diamond for high-power, mid-infrared laser sources (2.5-3 µm).
Core Challenge: Mitigating significant linear absorption loss caused by multi-phonon processes inherent to diamond in the 2.5-6.5 µm band.
Optimization Strategy: Numerical modeling determined that increasing the output coupling transmittance (T) and optimizing the diamond length (L) are essential to overcome absorption losses.
Key Achievement (Predicted): A 10% conversion efficiency for a 3 µm Stokes output is achievable under optimized resonator conditions.
Optimal Parameters: For 3 µm operation, the ideal configuration requires a diamond length of 1 cm and an output coupler transmittance of 69%.
Material Requirement: The high pump intensities (up to 1.2 GWcm^-2) and the need for low absorption necessitate ultra-high purity, optical-grade Single Crystal Diamond (SCD) with superior surface quality.
Diamond Advantages: Diamond remains the superior Raman medium due to its record-high thermal conductivity (2,000 W m^-1K^-1) and high damage threshold (3-4 GWcm^-2).

Technical Specifications

The following hard data points were extracted from the numerical simulation and material properties cited in the research:

Parameter	Value	Unit	Context
Raman Gain Coefficient (g)	17	cmGW^-1	High intrinsic gain of diamond
Thermal Conductivity	2,000	W m^-1K^-1	Record-high value (W m^-1K^-1)
Raman Shift	1,332.3	cm^-1	Fundamental shift
MIR Absorption Band	2.5-6.5	µm	Multi-phonon absorption region
Optimal Diamond Length (L)	1	cm	Optimized for 3 µm Stokes output
Optimal Transmittance (T)	69	%	Optimized output coupling for L=1 cm
Optimal Pump Intensity (I_p)	1.2	GWcm^-2	Required for 10% conversion efficiency
Predicted Conversion Efficiency	10	%	Maximum efficiency at 3 µm Stokes
Diamond Damage Threshold	3-4	GWcm^-2	High resistance to intense pump power
Stokes Wavelength Analyzed	3	µm	Target mid-infrared output
Corresponding Pump Wavelength (λ_p)	2.14	µm	Input wavelength for 3 µm Stokes

Key Methodologies

The research relied on numerical simulation to model the physical processes within the extra-cavity diamond Raman laser:

Model Construction: A theoretical model was established based on the Raman coupled-wave equation and boundary conditions, specifically tailored for the external-cavity configuration.
Loss Integration: The model explicitly incorporated linear absorption loss coefficients (a_p and a_s) derived from measured data, accurately reflecting the strong multi-phonon absorption present in the 2.5-6.5 µm band.
Resonator Optimization: The simulation systematically varied the two critical resonator parameters—diamond length (L) and output coupler transmittance (T)—to analyze their effect on lasing threshold and output intensity.
Temporal Analysis: The temporal behavior of Stokes conversion was investigated, confirming pulse-shortening effects typical of Raman lasers and verifying the theoretical analysis against known experimental results.
Design Recommendation: The analysis concluded that high-power operation in the MIR band necessitates a larger output coupler transmittance (T) and suggested using Brewster-cut diamond to avoid Fresnel reflection losses at the high operating intensities (GWcm^-2 magnitude).

6CCVD Solutions & Capabilities

The successful replication and extension of this high-power, mid-infrared Raman laser research depend entirely on the quality and customization of the diamond medium. 6CCVD is uniquely positioned to supply the necessary materials and engineering services.

Applicable Materials

The research requires diamond with ultra-low absorption coefficients and high thermal stability to handle GWcm^-2 pump intensities.

Material Recommendation: Optical Grade Single Crystal Diamond (SCD).
- Our MPCVD SCD is Type IIa, characterized by extremely low nitrogen content and minimal defects, ensuring the lowest possible linear propagation loss (a_p and a_s) in the critical 2.5-6.5 µm multi-phonon absorption band.
- This material guarantees the high thermal conductivity (2,000 W m^-1K^-1) necessary for managing thermal load under high-power pulsed operation.

Customization Potential

The optimization results (L=1 cm, Brewster-cut surfaces) highlight the need for precision material engineering, a core capability of 6CCVD.

Research Requirement	6CCVD Customization Capability	Specification
Optimized Length (L)	Custom Substrate Thickness	Substrates available up to 10 mm (1 cm) thick, cut to precise tolerances.
High Pump Intensity	Ultra-Smooth Polishing	SCD polishing guaranteed to Ra < 1 nm to minimize surface damage risk at 1.2 GWcm^-2.
Fresnel Loss Mitigation	Custom Laser Cutting & Polishing	We provide precision Brewster-cut diamond crystals, eliminating the need for traditional AR coatings that may degrade under high power.
Alternative Configurations	Custom Dimensions (PCD)	We offer Polycrystalline Diamond (PCD) plates up to 125 mm in diameter for scaling up or exploring alternative resonator geometries.
Metalization (If required)	Internal Metalization Services	We offer custom metalization stacks (Au, Pt, Pd, Ti, W, Cu) for engineers designing integrated or hybrid cavity structures.

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of diamond for nonlinear optics and high-power laser applications.

We provide expert consultation on material selection, orientation (e.g., <100> or <111>), and surface preparation to maximize Raman gain and minimize absorption losses for similar Mid-Infrared Raman Laser projects.
Our technical sales engineers can assist in translating complex numerical optimization results (like the L and T parameters found in this paper) into precise, manufacturable diamond specifications.

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

View Original Abstract

The physical process of stimulated Raman scattering (SRS) in the diamond and the performance of the Raman laser in the multi-phonon absorption band of 2.5-3 μm were theoretically studied. A theoretical model for the external-cavity diamond Raman laser emitting at the waveband was built based on the Raman coupled-wave equation and boundary conditions. Raman laser output characteristics such as lasing threshold, input-output, and temporal behavior of Stokes conversion were investigated and theoretically simulated by varying the values of the length of the diamond and the transmittance of the output coupler. The numerical modeling shows that to reduce the impact of the multi-phonon absorption and obtain a higher conversion efficiency, it is necessary to appropriately increase the output coupling of the cavity. Taking the 3 μm diamond Raman laser optimization as an example, it is predicted that the conversion efficiency of 10% could be obtained with a diamond length of 1 cm, a transmittance of 69%, and a pump intensity of 1.2 GWcm −2 . The theoretical model also could be used to investigate other wavelengths of the external-cavity diamond Raman laser and be helpful for the optimum design of diamond Raman lasers in the mid-infrared band.

Tech Support

Original Source

DOI: https://doi.org/10.3389/fphy.2022.1027998

References

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