A Narrow-Linewidth Linearly Polarized 1018-nm Fiber Source for Pumping Diamond Raman Laser

At a Glance

Metadata	Details
Publication Date	2021-08-16
Journal	Frontiers in Physics
Authors	Xuezong Yang, Zhenxu Bai, Huawei Jiang, Richard P. Mildren, Yan Feng
Institutions	University of Chinese Academy of Sciences, Shanghai Institute of Optics and Fine Mechanics
Citations	3
Analysis	Full AI Review Included

6CCVD Technical Documentation: Diamond Raman Laser Pumping Source Analysis

Reference Paper: Yang X, Bai Z, Jiang H, Mildren RP and Feng Y (2021) A Narrow-Linewidth Linearly Polarized 1018-nm Fiber Source for Pumping Diamond Raman Laser. Front. Phys. 9:727109.

Executive Summary

This research successfully demonstrates a high-power, narrow-linewidth fiber laser pump source for a diamond Raman laser (DRL), targeting the generation of 589 nm light for Sodium Guide Star applications.

High-Power Pumping: A linearly polarized 1,018 nm Yb-doped fiber laser (YDFL) achieved 75 W output power with 64% optical-to-optical conversion efficiency.
Narrow Linewidth: The pump source exhibited a narrow FWHM linewidth of 7.8 GHz, the narrowest reported at this power level for a 1,018 nm fiber laser.
Diamond Raman Conversion: The 1,018 nm source successfully pumped a standing-wave DRL cavity utilizing a high-quality, low-birefringence Single Crystal Diamond (SCD) element.
Stokes Output: Generated 6.1 W of first-order Stokes output at 1,178 nm, which is the precursor wavelength for 589 nm generation via frequency doubling.
Material Requirement: The DRL relied on a low-birefringence, low-nitrogen CVD-grown SCD (8 mm x 4 mm x 1.2 mm) to minimize thermal and depolarization effects.
Gain Enhancement: The narrow 7.8 GHz pump linewidth resulted in an effective Raman gain coefficient approximately 16% higher than that achieved with a 20 GHz pump source.
Mode Control: Demonstrated Single-Longitudinal-Mode (SLM) Stokes output (0.8 GHz FWHM) at lower pump powers, confirming the advantage of diamond’s homogeneous gain profile.

Technical Specifications

Parameter	Value	Unit	Context
Pump Wavelength	1,018	nm	Yb-doped fiber laser source
Stokes Wavelength	1,178	nm	First-order diamond Raman shift
Target Application Wavelength	589	nm	Frequency-doubled Stokes (Sodium Guide Star)
Maximum Pump Power (Amplifier)	75	W	Output after amplification stage
Optical-to-Optical Conversion Efficiency	64	%	1,018 nm amplifier efficiency
Pump Linewidth (FWHM)	7.8	GHz	Narrowest reported at this power level
SLM Stokes Linewidth (FWHM)	0.8	GHz	Measured at 0.6 W Stokes output
Maximum Stokes Output Power	6.1	W	Achieved at 63 W incident pump power
Diamond Raman Shift	39.99	THz	First-order shift frequency
Diamond Dimensions (L x W x T)	8 x 4 x 1.2	mm	Low-birefringence SCD element
Diamond Raman Gain Profile (FWHM)	45	GHz	For single frequency pumping
Pump Threshold (7.8 GHz pump)	9.3	W	DRL threshold
Pump Threshold (20 GHz pump)	11.4	W	Comparative DRL threshold (22.5% higher)

Key Methodologies

The experiment focused on optimizing the pump source and utilizing a high-quality diamond element within a standing-wave cavity.

Fiber Resonator Construction: A linear fiber resonator was established using a pair of narrow-bandwidth Fiber Bragg Gratings (FBGs) centered at 1,017.9 nm (HR FBG reflectivity: 98.5%; OC FBG reflectivity: 17%).
Active Fiber Selection: A large core-to-cladding ratio Yb-doped double-cladding fiber (LMA-YDF-15/130) was used to suppress Amplified Spontaneous Emission (ASE) at 1,030 nm.
Polarization Control: A fast-axis blocked Polarization-Maintaining (PM) optical isolator was inserted between the resonator and amplifier to ensure a linearly polarized output and prevent backward feedback.
Amplification: The amplifier stage utilized 0.9 m of PM LMA Yb-doped fiber (20/130 µm core/cladding) pumped by two 60 W 976 nm laser diodes.
Diamond Raman Cavity Setup: The collimated 1,018 nm pump was injected into a standing-wave near-concentric resonator using a plano-convex focusing lens (f = 50 mm).
Diamond Element: A low-birefringence, low-nitrogen, CVD-grown Single Crystal Diamond (SCD) element (8 mm x 4 mm x 1.2 mm) was inserted at the waist of the cavity.
Cavity Mirror Specifications: The Input Coupler was highly transmissive (>98%) at 1,018 nm and highly reflective (>99.9%) at 1,178 nm. The Output Coupler provided approximately 0.1% transmission at 1,178 nm.

6CCVD Solutions & Capabilities

The successful demonstration of a high-power diamond Raman laser relies critically on the quality, dimensions, and surface finish of the CVD diamond element. 6CCVD specializes in providing the exact material specifications required to replicate and advance this high-value research area, particularly for demanding applications like Sodium Guide Star lasers.

Applicable Materials

To replicate the low-loss, high-efficiency DRL demonstrated in this paper, researchers require the highest quality SCD.

Requirement from Paper	6CCVD Applicable Material	Technical Rationale
Low-birefringence, low-nitrogen, CVD-grown single crystal diamond	Optical Grade Single Crystal Diamond (SCD)	Our SCD material ensures minimal internal stress and low nitrogen content, critical for reducing absorption, thermal lensing, and depolarization loss in high-power Raman cavities.
High thermal conductivity	SCD Substrates	Diamond’s superior thermal properties (up to 2000 W/mK) are essential for rapidly dissipating heat (as noted in Ref. [15]), enabling high-power CW operation without spatial hole burning effects.

Customization Potential

The diamond used (8 mm x 4 mm x 1.2 mm) is a custom dimension. 6CCVD excels at providing components tailored precisely to cavity geometry and thermal management needs.

Research Requirement	6CCVD Customization Capability	Specification Range
Custom Dimensions	Precision laser cutting and shaping of plates/wafers.	Plates/wafers up to 125 mm (PCD). Custom dimensions for SCD elements.
Thickness Control	Manufacturing of specific thicknesses for optimal thermal and optical path length.	SCD thickness from 0.1 µm up to 500 µm. Substrates available up to 10 mm.
Surface Finish	Ultra-low loss surfaces required for high-Q resonant cavities.	Ra < 1 nm polishing for SCD (optical grade). Ra < 5 nm for inch-size PCD.
Integrated Optics/Thermal Sinking	Custom metalization services for heat management or electrical contacts (e.g., for BDD).	Internal capability for Au, Pt, Pd, Ti, W, Cu deposition.

Engineering Support

The paper highlights challenges related to pump stability and the impact of linewidth on effective Raman gain. 6CCVD’s in-house PhD team provides expert consultation to optimize material selection for similar high-power laser projects.

Material Optimization: Assistance in selecting the optimal SCD orientation and quality to minimize birefringence and maximize effective Raman gain coefficient (geff).
Thermal Management Design: Support in integrating diamond elements into high-power cavities, leveraging diamond’s thermal properties for stable CW operation.
Application Focus: Specialized support for high-power frequency conversion systems, including Sodium Guide Star lasers and other solid-state Raman applications.

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

View Original Abstract

A 7.8-GHz linewidth ytterbium-doped fiber (YDF) laser with an output power of 75 W at 1,018 nm is demonstrated based on narrow-bandwidth fiber Bragg gratings. Effective suppression of spectral broadening and amplified spontaneous emission is achieved by optimizing the resonator structure and active fiber parameters. An 1,178-nm diamond Raman output pumped by this narrow-linewidth 1,018 nm source is addressed in this study, which shows a promising application of generating the sodium guide star laser at 589 nm. A single-longitudinal-mode Stokes with an output power of 0.6 W is obtained using this multimode 1,018 nm laser at the pump power of 13 W. The impact of pump spectral linewidth on the effective Raman gain coefficient is analyzed, and the laser threshold of the diamond Stokes resonator increases with the broadening of the pump linewidth.

Tech Support

Original Source

DOI: https://doi.org/10.3389/fphy.2021.727109

References

2009 - New Developments in IPG Fiber Laser Technology
2011 - Power Scaling Analysis of Tandem-Pumped Yb-Doped Fiber Lasers and Amplifiers [Crossref]
2015 - Temporally Stable Random Fiber Laser Operates at 1070 Nm [Crossref]
2021 - 2196 W Large-Mode-Area Er:Yb Codoped Fiber Amplifier Operating at 1600 Nm Pumped by 1018 Nm Fiber Lasers [Crossref]
2017 - High-power 1018 Nm Ytterbium-Doped Fiber Laser with Output of 805 W [Crossref]
2013 - High Power 1018 Nm Ytterbium Doped Fiber Laser with an Output Power of 309 W [Crossref]
2017 - High-power Fiber Lasers Based on Tandem Pumping [Crossref]
2010 - kW Level Narrow Linewidth Yb Fiber Amplifiers for Beam Combining [Crossref]
1992 - Stable Fluorescent Complexes of Double-Stranded DNA with Bis-Intercalating Asymmetric Cyanine Dyes: Properties and Applications [Crossref]
2011 - Magneto-optical Trapping of Neutral Mercury [Crossref]