Diamond Raman laser - a promising high-beam-quality and low-thermal-effect laser
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-01-01 |
| Journal | High Power Laser Science and Engineering |
| Authors | Yulan Li, Jie Ding, Zhenxu Bai, Xuezong Yang, Yuqi Li |
| Institutions | Hebei University of Technology, Macquarie University |
| Citations | 31 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThe research details the development and performance optimization of Diamond Raman Lasers (DRLs), highlighting diamondâs unique material properties that enable superior laser output characteristics compared to other solid-state media.
- Core Value Proposition: Diamondâs exceptional thermal conductivity (2200 W/mK) and high Raman gain coefficient allow DRLs to achieve high-power output while maintaining excellent beam quality and minimizing thermal degradation (thermal lensing).
- Power Scaling Achievement: DRLs have successfully achieved kilowatt-level output, reaching 1.2 kW in quasi-CW operation, demonstrating power scaling comparable to high-power Raman fiber lasers.
- Beam Quality Enhancement (Raman Cleanup): The Raman conversion process inherently acts as a âcleanupâ effect. DRLs consistently produce near-diffraction-limited output (M2 < 1.1), even when pumped by medium-quality beams (M2 up to 7.3).
- Wavelength Versatility: Cascaded Stokes shifting in diamond enables broad spectral coverage, with successful demonstrations spanning deep ultraviolet (275.7 nm) to mid-infrared (3.8 ”m).
- Coherence Control: Stable Single Longitudinal Mode (SLM) operation has been realized, often stabilized by incorporating additional gain competition mechanisms like intracavity frequency doubling.
- Limiting Factor: Despite diamondâs thermal advantages, thermal lensing effects in the resonant cavity remain the primary obstacle limiting further power scaling and optimization under strong focusing conditions.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Thermal Conductivity (Diamond) | 2200 | W·m-1·K-1 | Highest among common Raman materials |
| Raman Gain Coefficient (Diamond) | 10-12 | cm/GW | Measured @ 1064 nm pump wavelength |
| Raman Shift (Diamond) | 1332.3 | cm-1 | Large shift enables rapid wavelength conversion |
| Transmission Range (Diamond) | > 0.23 | ”m | Wide spectral range (Deep UV to Mid-IR) |
| Thermal Expansion Coefficient (Diamond) | 1.1 | x10-6 K-1 | Extremely low, minimizing thermal stress |
| Highest Quasi-CW Output Power | 1.2 | kW | Achieved @ 1240 nm (First Stokes) |
| Optical-to-Optical Conversion Efficiency | 53 | % | Achieved during 1.2 kW quasi-CW operation |
| Best Beam Quality Factor (M2) | < 1.1 | N/A | Near-diffraction-limited output |
| SLM Output Power (589 nm) | 22 | W | CW operation with intracavity frequency doubling |
| Mid-Infrared Output Wavelength | 3.38-3.80 | ”m | Generated using tunable optical parametric oscillator pump |
| Thermal Lens Strength (Calculated Max) | 16 | Diopters | Observed during high-power pulsed operation |
| Typical Thermal Gradient Establishment Time | ~10 | ”s | Allows stable quasi-CW operation |
Key Methodologies
Section titled âKey MethodologiesâThe development and optimization of DRLs rely on specific engineering and material science techniques:
- CVD Diamond Utilization: High-quality, large-area Chemical Vapor Deposition (CVD) diamond is used as the gain medium, providing the necessary purity and size uniformity required for high-power laser operation.
- External Cavity Design: The laser structure is typically an external-cavity pumped configuration. This design isolates the diamond Raman resonator from the pump laser, simplifying thermal management and reducing the influence of thermal effects from the pump source.
- Raman Cleanup Effect Exploitation: DRLs are often pumped by medium-beam-quality lasers (M2 up to 7.3). The inherent self-phase matching capability of the SRS process filters out higher-order spatial modes, resulting in high-quality, near-TEM00 output (M2 < 1.1).
- Cascaded Wavelength Conversion: Multi-stage Raman resonators are used to achieve cascaded Stokes shifts, enabling conversion from common pump wavelengths (e.g., 1.06 ”m) into critical bands like the eye-safe 1.5 ”m region (via second-order Stokes shift).
- SLM Stabilization via Harmonic Mixing: To achieve stable Single Longitudinal Mode (SLM) output, researchers introduce additional gain competition, such as intracavity Second Harmonic Generation (SHG) using crystals like LBO, which suppresses the instability caused by thermally induced cavity length changes.
- Thermal Lens Modeling: Thermal effects are analyzed using finite-element-analysis (FEA) models (e.g., QuickField) combined with modified CW end-pumped rod laser equations. This modeling estimates the thermal lens focal length (f-1) based on deposited heat (Pdep) and the thermo-optic coefficient (dn/dT).
Commercial Applications
Section titled âCommercial ApplicationsâThe unique combination of high power, high beam quality, and wide spectral access provided by DRLs makes them suitable for advanced engineering applications:
- Defense and Directed Energy: High-brightness laser sources are critical for directional energy applications, benefiting from the DRLâs high power and excellent beam quality.
- Remote Sensing and Lidar: The efficient generation of eye-safe wavelengths (around 1.5 ”m) is essential for long-range atmospheric sensing and ranging systems.
- Precision Material Processing: High-power CW DRLs with near-diffraction-limited beams are ideal for high-precision cutting, drilling, and welding of materials.
- Mid-Infrared Countermeasures and Spectroscopy: Access to the mid-infrared region (3-6 ”m) supports applications in chemical detection, environmental monitoring, and infrared countermeasures.
- Ultraviolet Manufacturing: The ability to convert to deep ultraviolet wavelengths (less than 300 nm) opens possibilities for advanced lithography and specialized material modification.
- High-Coherence Systems: Stable SLM operation is required for high-resolution spectroscopy, coherent communications, and advanced scientific instrumentation.
View Original Abstract
Abstract Stimulated Raman-scattering-based lasers provide an effective way to achieve wavelength conversion. However, thermally induced beam degradation is a notorious obstacle to power scaling and it also limits the applicable range where high output beam quality is needed. Considerable research efforts have been devoted to developing Raman materials, with diamond being a promising candidate to acquire wavelength-versatile, high-power, and high-quality output beam owing to its excellent thermal properties, high Raman gain coefficient, and wide transmission range. The diamond Raman resonator is usually designed as an external-cavity pumped structure, which can easily eliminate the negative thermal effects of intracavity laser crystals. Diamond Raman converters also provide an approach to improve the beam quality owing to the Raman cleanup effect. This review outlines the research status of diamond Raman lasers, including beam quality optimization, Raman conversion, thermal effects, and prospects for future development directions.