Eye-safe intra-cavity diamond cascaded Raman laser with high peak-power and narrow linewidth

At a Glance

Metadata	Details
Publication Date	2024-01-01
Journal	Chinese Optics Letters
Authors	Xiaobo Mi, Chaonan Lin, Yongsheng Hu, Houjie Ma, Jiuru He
Institutions	Yangzhou University, Zhengzhou University
Citations	8
Analysis	Full AI Review Included

Technical Documentation & Analysis: High Peak-Power Diamond Raman Lasers

This document analyzes the research paper, “Eye-safe intra-cavity diamond cascaded Raman laser with high peak-power and narrow linewidth,” to provide technical specifications and align the findings with 6CCVD’s advanced MPCVD diamond solutions.

Executive Summary

This research successfully demonstrates a highly efficient, eye-safe, intra-cavity diamond cascaded Raman laser, achieving record peak power and ultra-narrow linewidth, validating the critical role of high-quality CVD diamond in advanced photonics.

Record Peak Power: Achieved 40 kW peak power at the second-Stokes wavelength (1485.9 nm), the highest reported for eye-safe diamond Raman lasers to date.
Ultra-Narrow Linewidth: The device operates in a single longitudinal mode with a spectral width of < 0.02 nm, crucial for high-resolution applications like LIDAR.
Pulse Compression: The intra-cavity cascaded Raman process drastically compressed the pulse width from 60 ns (fundamental) to 1.1 ns (second-Stokes).
High Efficiency: Demonstrated an average output power of 2.2 W at 50 kHz PRF, corresponding to an 8.1% diode-to-second-Stokes conversion efficiency.
Material Criticality: The use of high-thermal-conductivity CVD diamond (2200 W/mK) in a V-shaped folded cavity design was essential for thermal stability and efficient mode matching under high pump power.
Future Optimization: The authors noted that performance is highly sensitive to intracavity losses and suggested the use of Anti-Reflection (AR) coatings on the diamond to further improve efficiency—a key capability offered by 6CCVD.

Technical Specifications

The following hard data points were extracted from the experimental results:

Parameter	Value	Unit	Context
Second-Stokes Wavelength	1485.9	nm	Eye-safe output
Fundamental Wavelength	1064	nm	Nd:YVO₄ emission
Pump Wavelength	880	nm	Fiber-coupled LD
Average Output Power (Second-Stokes)	2.2	W	At 50 kHz PRF
Peak Power (Second-Stokes)	40	kW	Highest reported
Pulse Width (Second-Stokes)	1.1	ns	Result of Raman pulse compression
Spectral Linewidth	< 0.02	nm	Single longitudinal mode operation
Diode to Second-Stokes Efficiency	8.1	%	Conversion efficiency
Diamond Dimensions	2 x 2 x 7	mm	Uncoated CVD-diamond
Diamond Thermal Conductivity	2200	W/mK	Key material property
Raman Shift	1332.3	cm^-1	Diamond characteristic
Beam Quality (M²)	1.33 (H), 1.76 (V)	N/A	Measured at maximum output power
Cooling Temperature	18	°C	Water cooling for crystals

Key Methodologies

The high performance was achieved through a combination of optimized cavity design, thermal management, and material selection:

Pumping Scheme: Utilized in-band pumping via a 65 W, 880 nm fiber-coupled laser diode to excite a composite Nd:YVO₄ crystal, effectively mitigating thermal effects in the gain medium.
Raman Crystal: An uncoated CVD-diamond crystal (2 mm x 2 mm x 7 mm) was used, cut for beam propagation in the (110) direction. Fundamental laser polarization was matched to the diamond (111) direction to maximize Raman gain.
Cavity Geometry: A V-shaped folded cavity was implemented to ensure optimal mode matching and high thermal stability, resulting in a small fundamental laser spot (72 µm x 80 µm) on the diamond.
Cascaded Conversion: The output coupler (M4) was designed with high reflection (R > 99.8%) at the fundamental (1064 nm) and first-Stokes (1240 nm) wavelengths, forcing efficient cascaded conversion to the second-Stokes (1485 nm).
Pulse Generation: Active Q-switching was performed using an acousto-optic Q-switch (AOS) at a Pulse Repetition Frequency (PRF) of 50 kHz.
Thermal Control: Both the Nd:YVO₄ and the diamond were actively cooled to 18°C using a water-cooled copper block.
Short Cavity: The Raman cavity length was minimized to 10 mm, which contributed to the observed single longitudinal mode operation and enhanced pulse compression.

6CCVD Solutions & Capabilities

The success of this high peak-power Raman laser hinges entirely on the quality and customization of the Single Crystal Diamond (SCD) element. 6CCVD is uniquely positioned to supply the required materials and advanced fabrication services necessary to replicate this research or extend its performance, particularly by addressing the authors’ noted limitations regarding intracavity loss.

Requirement from Research Paper	6CCVD Solution & Value Proposition
Applicable Materials	Optical Grade Single Crystal Diamond (SCD): Required for its ultra-high thermal conductivity (2200 W/mK) and high Raman gain coefficient. 6CCVD SCD features extremely low nitrogen content, minimizing absorption losses critical for high-power intra-cavity systems.
Custom Dimensions & Orientation	Precision Fabrication: The paper used a 2 mm x 2 mm x 7 mm crystal with (110) propagation. 6CCVD specializes in custom SCD plates and substrates up to 10 mm thick, ensuring precise dimensions and guaranteeing specific crystallographic orientations required for optimal Raman gain matching.
Addressing Intracavity Loss (Sales Hook)	Ultra-Low Roughness Polishing (Ra < 1 nm): The V-shaped cavity is highly sensitive to scattering losses. Our SCD material is polished to Ra < 1 nm, significantly surpassing standard commercial quality and ensuring minimal loss in the 10 mm Raman cavity.
Need for AR Coating (Explicitly suggested by authors)	Integrated Metalization & Coating Services: The authors noted that AR coating the diamond would further improve efficiency. 6CCVD offers custom thin-film deposition and metalization (e.g., Ti/Pt/Au) and facilitates the application of custom dielectric AR coatings optimized for the fundamental (1064 nm) and Stokes (1485 nm) wavelengths, eliminating Fresnel losses.
High Peak Power Handling	Thermal Stability Assurance: For applications demanding 40 kW peak power, 6CCVD SCD provides the necessary thermal management foundation, ensuring stable operation and preventing thermal lensing effects that degrade beam quality (M²).

Engineering Support

6CCVD’s in-house PhD engineering team specializes in optimizing diamond material parameters (purity, orientation, and surface finish) for high-power, cascaded Raman laser systems. We offer consultation on material selection, thermal modeling, and custom coating specifications for similar high peak-power, high-resolution LIDAR projects.

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

View Original Abstract

The 1.4-1.8 µm eye-safe lasers have been widely used in the fields of laser medicine and laser detection and ranging. The diamond Raman lasers are capable of delivering excellent characteristics, such as good beam quality concomitantly with high output power. The intra-cavity diamond Raman lasers have the advantages of compactness and low Raman thresholds compared to the external-cavity Raman lasers. However, to date, the intra-cavity diamond cascaded Raman lasers in the spectral region of the eye-safe laser have an output power of only a few hundred milliwatts. A 1485 nm Nd:YVO4/diamond intra-cavity cascaded Raman laser is reported in this paper. The mode matching and stability of the cavity were optimally designed by a V-shaped folded cavity, which yielded an average output power of up to 2.2 W at a pulse repetition frequency of 50 kHz with a diode to second-Stokes conversion efficiency of 8.1%. Meanwhile, the pulse width of the second-Stokes laser was drastically reduced from 60 ns of the fundamental laser to 1.1 ns, which resulted in a high peak power of 40 kW. The device also exhibited single longitudinal mode with a narrow spectral width of < 0.02 nm.

Tech Support

Original Source

DOI: https://doi.org/10.3788/col202422.041402

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