Dual-Substrate Dichroic Beam Combiner Thermal Lensing
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Solution Overview
Problem
Conventional dichroic beam combiners experience heating issues due to laser light absorption, leading to thermal expansion and non-uniform refractive index changes, which disrupt the collimation and focusing of combined laser beams, limiting the achievable power.
Innovation Solution
A dual-substrate dichroic beam combiner is introduced, where the dichroic filter is sandwiched between two substrates. This design ensures that both the transmitted and reflected input beams are affected similarly by heating, maintaining consistent focusing properties and preventing focusing discrepancies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional single-substrate dichroic beam combiner is used, then the device complexity is low, but thermal effects cause focusing discrepancies between transmitted and reflected beams
Solution Approach 1:
The single substrate is divided into two separate substrates, allowing independent thermal management and optical path control. Each substrate can be optimized for its specific function (transmission or reflection) without compromising the other, thereby maintaining focusing consistency even under thermal load.
Solution Approach 2:
A thermal management layer or interface layer is introduced between the dichroic filter and the substrates to mediate heat distribution. This intermediary layer helps equalize thermal effects across both optical paths, preventing differential thermal expansion and refractive index changes that would cause focusing discrepancies.
2Power
If high laser power is combined using conventional dichroic filters, then the power handling capability increases, but thermal expansion and refractive index changes disrupt beam collimation
Solution Approach 1:
The thermal parameters (temperature distribution, thermal conductivity) of the substrate materials are carefully selected and engineered to minimize thermal expansion and refractive index changes. By changing material parameters and optimizing thermal design, the system maintains beam collimation stability even at high combined powers.
Solution Approach 2:
Composite substrate structures are used, combining materials with complementary thermal and optical properties. The composite design allows one material to handle thermal loads while the other maintains optical precision, enabling high power handling without compromising collimation stability.
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 dual-substrate design allows for the combination of high-power laser beams with consistent focusing, enabling the achievement of higher average powers without the limitations imposed by thermal effects in conventional combiners.
Implementation Method 1
a dichroic thin-film filter coated at a nominally planar interface between the substrates. The dichroic thin-film filter is transmissive in a transmission-wavelength-range and reflective in a reflection-wavelength-range
Implementation Method 2
Each dichroic beam combiner includes a dichroic thin-film interference filter that reflects one of the two input beams and transmits the other
Implementation Method 3
heating of the dichroic beam combiners caused by absorption of laser light in the dichroic filters
Implementation Method 4
the heating is sufficient to induce thermal expansion of the substrate and/or non-uniform changes in its refractive index
Implementation Method 5
non-uniform changes in its refractive index. The interference filter is very thin. Yet, at high laser powers, the heating is sufficient to induce thermal expansion of the substrate and/or non-uniform changes in its refractive index
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A dual-substrate dichroic beam combiner (100) includes two substrates (110,120), and a dichroic thin-film filter (130) coated at a nominally planar interface between the substrates. The filter (130) is configured to combine, into a combined laser beam (194), two input laser beams (190,192) that are incident on the filter (130) of the combiner (100) from opposite respective sides thereof. One input beam (190) is transmitted by the combiner (100), while the other input beam (192) is reflected. The substrates (110,120) are configured to, when heated by absorption of the input laser beams (190,192) in the filter (130), form a lens for each of the input laser beams (190,192). The lens is either (a) a negative lens for each of the input laser beams (190,192) or (b) a positive lens for each of the input laser beams (190,192). The combiner (100) thereby reduces or eliminates focusing discrepancies between the two input beams (190,192), in the combined beam (194), as compared to a conventional single-substrate dichroic beam combiner.