Power Scaling of CW Crystalline OPOs and Raman Lasers

At a Glance

Metadata	Details
Publication Date	2021-12-10
Journal	Photonics
Authors	Soumya Sarang, Martin Richardson
Institutions	University of Central Florida
Citations	4
Analysis	Full AI Review Included

Technical Documentation & Analysis: Power Scaling of CW Crystalline OPOs and Raman Lasers

This document analyzes the findings of the research review on power scaling in continuous-wave (CW) Optical Parametric Oscillators (OPOs) and Raman Lasers, focusing specifically on the critical role of diamond as the superior gain medium. This analysis is designed to provide technical insight and highlight how 6CCVD’s advanced MPCVD diamond capabilities directly support and enable the next generation of high-power, high-brightness Diamond Raman Lasers (DRLs).

Executive Summary

The research confirms that Diamond Raman Lasers (DRLs) offer the most promising path for power and brightness scaling in CW nonlinear frequency conversion technologies.

Thermal Superiority: Diamond’s extraordinary thermal conductivity (2000 W/mK) is approximately three orders of magnitude higher than conventional OPO and Raman crystals (e.g., LiNbO₃, KGW), making it uniquely resistant to thermal lensing and fracture.
Kilowatt Performance: Quasi-CW DRLs have demonstrated output powers up to 1.2 kW at 1240 nm, significantly surpassing the output limits of OPOs and non-diamond Raman lasers, which are restricted to the watt or low-hundreds-of-watts regime by thermal effects.
Brightness Enhancement: DRLs exhibit exceptional beam cleanup via the Stimulated Raman Scattering (SRS) mechanism, achieving a record Brightness Enhancement Factor (BEF) of 56 and converting low-quality pump beams (M² = 15) into near-diffraction-limited output (M² = 1.25).
Spectral Versatility: Diamond’s wide optical transparency (0.23 µm to 100 µm) and high Raman shift (1332.3 cm^-1) enable broad wavelength access from the UV to the mid-IR, crucial for applications like LIDAR and directed energy.
Future Focus: The primary challenge for achieving multi-kilowatt CW DRLs lies in optimizing thermal management and cooling architectures, a requirement directly addressed by 6CCVD’s custom material and metalization services.

Technical Specifications

The following table summarizes the key material properties of diamond and the demonstrated performance metrics of DRLs, as extracted from the review.

Parameter	Value	Unit	Context
Thermal Conductivity (Diamond)	2000	W/mK	At Room Temperature (Highest among all reviewed crystals)
Raman Gain Coefficient	10	cm/GW	@ 1064 nm
Raman Shift	1332.3	cm^-1	Fundamental shift
Optical Transparency Range	0.23 - 100	µm	UV to mid-IR
Maximum Output Power (Quasi-CW DRL)	1.2	kW	Demonstrated at 1240 nm [Ref 52]
Brightness Enhancement Factor (BEF)	56	N/A	Highest reported for crystalline Raman lasers [Ref 52]
Output Beam Quality (M²)	1.25	N/A	Achieved at 1.2 kW output power [Ref 52]
Birefringence (High-Quality SCD)	<10^-5	N/A	Perpendicular to growth direction
Typical Crystal Lengths Used	3.3 - 9.5	mm	For CW/quasi-CW DRLs

Key Methodologies

The successful power scaling and brightness enhancement demonstrated by DRLs rely on specific material selection and cavity architectures:

Gain Medium Selection: High-optical-quality Single Crystal Diamond (SCD) is mandatory. The material must exhibit ultra-low nitrogen impurity levels (20-40 ppb) and minimal absorption coefficients (0.001-0.004 cm^-1 at 1064 nm) to minimize parasitic heating.
Cavity Configuration: The External Cavity architecture is preferred for CW DRL power scaling. This configuration separates the pump laser and the Raman crystal, simplifying the design and enabling the use of high-damage-threshold diamond.
Nonlinear Process: Stimulated Raman Scattering (SRS) is utilized. Unlike OPOs (which require stringent phase-matching), SRS is a third-order ($\chi^{(3)}$) non-parametric process where phase-matching is always satisfied, simplifying the laser architecture and tuning.
Brightness Mechanism: The inherent “Raman Beam Cleanup (RBC)” mechanism of SRS is exploited. This allows the DRL to convert lower-quality, high-power pump beams into high-quality, near-diffraction-limited Stokes output beams.
Future Thermal Management: The review identifies that future multi-kilowatt CW operation requires advanced thermal management strategies, including specialized laser cooling mounts, cryogenics, and enhanced heat transfer coefficients in cooling pipes.

6CCVD Solutions & Capabilities

6CCVD is positioned as the essential material supplier and engineering partner for researchers and engineers developing next-generation DRLs. Our MPCVD diamond capabilities directly address the material specifications and thermal challenges identified in this review.

Applicable Materials

To replicate or extend the kilowatt-level DRL research, high-purity, low-birefringence diamond is required:

Optical Grade Single Crystal Diamond (SCD): 6CCVD supplies high-quality SCD necessary for minimizing intrinsic absorption and birefringence (<10^-5), which are critical for maintaining high conversion efficiency and beam quality (M² < 1.5) at high power levels.
Custom Substrates: The paper notes DRLs use crystals typically 3.3 mm to 9.5 mm in length. 6CCVD offers custom SCD substrates up to 500 µm thick and bulk substrates up to 10 mm thick, perfectly matching the required gain medium dimensions.

Customization Potential

The transition to multi-kilowatt CW DRLs necessitates robust thermal interfaces and precise crystal geometry. 6CCVD provides comprehensive customization services:

DRL Requirement	6CCVD Capability	Technical Advantage
Thermal Interface	Custom Metalization: Au, Pt, Pd, Ti, W, Cu layers applied directly to the diamond surface.	Enables robust, low-thermal-resistance bonding to cooling mounts (cryogenics, liquid cooling), addressing the critical need for heat dissipation identified in the review.
Optical Quality	Precision Polishing: SCD surfaces polished to Ra < 1 nm.	Essential for achieving the high laser-induced damage threshold (LIDT) and high-finesse cavities required for efficient CW SRS operation.
Scaling & Aperture	Large Dimensions: SCD plates up to 125 mm (PCD) diameter available.	Supports future research into large-aperture, high-power DRL architectures for multi-kilowatt directed energy applications.
Geometry	Custom Cutting: Precision laser cutting and shaping services.	Allows for complex crystal geometries required for specific cavity designs (e.g., thin-disk or slab configurations) to optimize thermal management.

Engineering Support

The review concludes that the future of DRL power scaling hinges on solving thermal management challenges.

Material Consultation: 6CCVD’s in-house PhD team specializes in the thermal, optical, and mechanical properties of MPCVD diamond. We provide expert consultation on material selection (SCD vs. PCD, doping levels) for similar High-Power Frequency Conversion projects.
Thermal Design Assistance: We assist engineers in specifying optimal diamond thickness, surface preparation, and metalization schemes to maximize heat transfer coefficients and minimize thermal lensing effects, directly supporting the research path outlined in the paper.
Global Logistics: We ensure reliable, global delivery of high-value diamond components (DDU default, DDP available) to keep critical research timelines on track.

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

View Original Abstract

Optical parametric oscillators (OPOs) and Raman lasers are two nonlinear-based laser technologies that extend the spectral range of conventional inversion lasers. Power and brightness scaling of lasers are significant for many applications in industry, medicine, and defense. Considerable advances have been made to enhance the power and brightness of inversion lasers. However, research around the power scaling of nonlinear lasers is lacking. This paper reviews the development and progress of output power of continuous-wave (CW) crystalline OPOs and Raman lasers. We further evaluate the power scalability of these two laser technologies by analyzing the cavity architectures and gain materials used in these lasers. This paper also discusses why diamond Raman lasers (DRLs) show tremendous potential as a single laser source for generating exceedingly high output powers and high brightness.

Tech Support

Original Source

DOI: https://doi.org/10.3390/photonics8120565

References

2004 - Efficient, all-solid-state, Raman laser in the yellow, orange and red [Crossref]
2020 - Watt-level CW Ti: Sapphire oscillator directly pumped with green laser diodes module [Crossref]
2021 - Review of laser-diode pumped Ti: Sapphire laser [Crossref]
1977 - 33-W CW dye laser [Crossref]