Dual-Grating Spectral Beam Combining With Diverging Laser Beams
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Solution Overview
Problem
Conventional grating-based spectral beam combiners are limited in combining a large number of laser beams due to damage threshold constraints and thermal aberrations, resulting in impracticality for high-power applications, especially when using collimated beams.
Innovation Solution
A dual-grating spectral beam combiner design that operates with diverging laser beams, allowing for the combination of multiple beams using two diffraction gratings with equal and opposite angular dispersion, which cancels divergence-induced errors and reduces aberrations, enabling a more compact and efficient high-power laser combination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional grating-based spectral beam combiners use collimated beams, then beam combination is achieved, but the damage threshold of the diffraction grating is exceeded and thermal aberrations occur when combining a large number of high-power beams
Solution Approach 1:
The patent segments the single large-aperture grating into multiple smaller sub-gratings arranged in series. Each sub-grating handles a portion of the total beam power, distributing the thermal load and preventing any single grating element from exceeding its damage threshold. This allows combination of many high-power beams while maintaining grating reliability.
Solution Approach 2:
The patent transitions from a two-dimensional array of beams (limited by grating aperture) to a three-dimensional configuration where beams are combined through multiple sequential grating stages. This adds a temporal/dimensional dimension to the combination process, allowing scaling to higher powers by adding more grating stages rather than increasing single-grating aperture.
2Power
If conventional grating-based spectral beam combiners use collimated beams, then beam combination is achieved, but the system becomes impractically large and complex when combining a large number of beams
Solution Approach 1:
The patent segments both the beam array and the grating structure into manageable units. Multiple sub-gratings are arranged in a compact sequential configuration, and the beam array is divided into groups that can be processed by each sub-grating stage, making the overall system more manageable and less complex than a single large-aperture design.
Solution Approach 2:
The patent employs a nested configuration where multiple sub-gratings are arranged in series, with each sub-grating processing a subset of beams. This nested structure allows the system to scale by adding more compact stages rather than expanding a single large component, reducing overall system complexity.
3Power
If conventional grating-based spectral beam combiners use collimated beams, then beam combination is achieved, but the propagation distance and grating size become unreasonably large
Solution Approach 1:
The patent segments the combination process into multiple short-stage sequential operations rather than requiring a single long propagation path. Each sub-grating stage handles a portion of the combination in a compact configuration, reducing the overall propagation distance needed compared to a single large-aperture grating system.
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
This approach enables the combination of a large number of laser beams with reasonably sized gratings and shorter propagation distances, maintaining good beam quality while overcoming the limitations of conventional systems, although it may result in a slight reduction in beam quality compared to single-grating combiners.
Implementation Method 1
a diffraction grating or even a series of dichroic mirrors, to combine several laser beams of different respective frequencies
Implementation Method 2
Diffraction by the first diffraction grating converts inter-beam spectral dispersion to inter-beam angular dispersion. The second diffraction grating is positioned at this location. Diffraction by the second grating imposes an angular dispersion that is equal and opposite to the angular dispersion imposed by the first grating.
Data Source
AI summary
A dual-grating spectral beam combiner includes a series of sources emitting a respective series of diverging laser beams with mutually parallel center rays offset from each other in a one-dimensional array. The laser beam wavelengths are incremented monotonically across the array. A first diffraction grating receives the diverging laser beams from the sources and diffracts the diverging laser beams to form respective once-diffracted diverging beams with mutually converging center rays. A second diffraction grating is positioned where the center rays of the once-diffracted diverging beams coincide, and diffracts the once-diffracted diverging beams to form a single combined diverging laser beam consisting of twice-diffracted diverging beams. The combined diverging laser beam may be subsequently collimated. By operating the dual-grating spectral beam combiner with diverging beams, it is possible to combine a high number of laser beams while keeping the propagation path between the two gratings short without requiring narrow linewidths.