Fiber-Delivered Laser Source for Spin Exchange Optical Pumping
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Solution Overview
Problem
High-power laser diodes with broad spectral bandwidths are not suitable for long-term spin-exchange optical pumping applications, such as neutron spin filters, due to instability and inefficiency in matching the pressure-broadened absorption lines of rubidium vapor, leading to reduced efficiency and overheating issues.
Innovation Solution
A stable, narrow spectral linewidth fiber-delivered laser source is developed using an optimized external cavity with a volume holographic grating to narrow the spectral linewidth of high-power diode lasers, achieving a side mode suppression ratio of >30 dB and long-term stability, and combining multiple laser diode arrays to increase power while maintaining a narrow spectral bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high-power laser diodes with broad spectral bandwidth are used, then high power output is achieved, but spectral stability and matching with rubidium absorption line deteriorate
Solution Approach 1:
An external cavity with volume holographic grating is introduced as an intermediary element between the laser diode and the target. This external cavity acts as a spectral filter that narrows the bandwidth and stabilizes the wavelength while preserving the high power output capability of the original laser diode.
Solution Approach 2:
The laser system is segmented into multiple functional components: the high-power laser diode array for power generation, the external cavity with volume holographic grating for spectral narrowing and stabilization, and the fiber delivery system. This segmentation allows each component to optimize its specific function without compromising overall performance.
2Power
If high-power laser diodes with broad spectral bandwidth are used, then high power output is achieved, but optical pumping efficiency deteriorates
Solution Approach 1:
The external cavity with volume holographic grating serves as a spectral matching intermediary that shapes the laser output spectrum to precisely match the rubidium D1 absorption line. This ensures maximum optical pumping efficiency by concentrating the laser power within the absorption bandwidth of the target atoms.
3Power
If high-power laser diodes are used, then high power output is achieved, but wavelength drift increases
Solution Approach 1:
The external cavity configuration provides inherent feedback stabilization. The volume holographic grating reflects specific wavelengths back into the laser diode cavity, creating a feedback mechanism that actively stabilizes the operating wavelength against drift caused by temperature changes or current variations in high-power operation.
Solution Approach 2:
The external cavity with volume holographic grating acts as a wavelength-stabilizing intermediary that decouples the wavelength stability from the power output. This allows the laser diode to operate at high power while the external cavity maintains precise wavelength control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a highly stable and efficient laser source with a spectral bandwidth matching the pressure-broadened rubidium D1 absorption line, achieving higher 3He polarization efficiency and reducing overheating, with the ability to scale power while maintaining spectral stability, thus enhancing the performance of spin-exchange optical pumping systems.
Implementation Method 1
an optimized external cavity equipped with a volume holographic grating (VHG) is used to narrow the spectral line-width of a 100 Watt high power diode laser and to stabilize the laser spectrum
Implementation Method 2
a laser delivered by a multi-mode fiber with power of about 70 Watts
Implementation Method 3
optical pumping of alkali metal vapors, typically rubidium. Such optical pumping can be used to polarize various atoms, such as 3He or 129Xe atoms
Implementation Method 4
the polarization of electron is transferred to 3He atoms via hyperfine interaction
Data Source
AI summary
Disclosed herein are example embodiments for providing high power, narrow linewidth, high-stability laser sources. Particular embodiments are adapted for use in spin exchange optical pumping (SEOP). One example system comprises an array of laser diodes; a beam twister positioned to receive individual beamlets from the array of laser diodes, the beam twister being configured to rotate the individual beamlets from the array of laser diodes and produce rotated beamlets; one or more collimating lenses positioned to receive the rotated beamlets produced by the beam twister and produce substantially collimated beamlets having a divergence angle; a spectral-line-width-reducing element positioned to receive the substantially collimated beamlets from the one or more collimating lenses and produce spectral-line-width-reduced beamlets; an optical fiber; and one or more focusing lenses positioned between the optical fiber and the spectral-line-width-reducing element and configured to receive the spectral-line-width-reduced beamlets and focus them into the optical fiber.