The primary function of a Spherical Biconvex Lens in a dual-spot laser system is to act as a collimating element. It is strategically positioned to intercept the naturally divergent laser beam exiting an optical fiber and transform it into a parallel, collimated beam. This conversion is the critical prerequisite for any subsequent beam splitting, shaping, or focusing within the system.
By converting the spreading light from the optical fiber into a straight, parallel path, this lens establishes the geometric foundation required for accurate dual-spot generation. It dictates the initial consistency and stability of the laser energy before it is split or focused.
The Mechanics of Beam Transformation
Correcting Beam Divergence
Laser light exiting an optical fiber does not travel in a straight line; it expands in a cone shape.
The Spherical Biconvex Lens captures this expanding cone. Its geometry bends the light rays inward, effectively canceling out the divergence. The result is a beam where light rays travel parallel to the optical axis.
The Role of Focal Length
To achieve true collimation, the position of the lens is non-negotiable.
The lens must be placed at a distance exactly equal to its focal length from the tip of the optical fiber. If the lens is too close or too far, the beam will either converge too early or continue to diverge, compromising the entire optical train.
Impact on System Performance
enabling Spot Shaping
Collimation is not the end goal; it is a preparatory step.
The primary reference notes that this process is fundamental for subsequent spot shaping and size adjustment. Optical components designed to split the beam into "dual spots" generally require a parallel input to function predictable. Without this initial collimation, the final spots would be distorted or sized incorrectly.
Determining Output Stability
The quality of the final laser spot depends heavily on this initial lens.
The lens determines the shape stability of the output. If the collimation is inconsistent, the final energy density at the workpiece will fluctuate, leading to unreliable laser processing results.
Understanding the Trade-offs
Sensitivity to Alignment
While a biconvex lens is efficient, it requires high mechanical precision.
Because the collimation quality relies entirely on the specific distance from the fiber (the focal length), any mechanical vibration or thermal expansion that shifts this distance will immediately degrade the beam quality.
Spherical Aberration Limits
It is important to note the physical limitations of a spherical lens surface.
Spherical lenses cannot focus all rays perfectly to the same point, particularly those hitting the edges of the lens. While effective for general collimation, this can introduce slight "softness" or haloing in the beam profile compared to more expensive aspheric alternatives.
Optimizing Your Optical Setup
To ensure your dual-spot system functions correctly, you must view this lens as the anchor of your optical path.
- If your primary focus is Beam Consistency: Ensure the distance between the fiber tip and the lens is mechanically locked and thermally stable to maintain parallel output.
- If your primary focus is Spot Precision: Verify that the lens diameter is sufficient to capture the entire numerical aperture (cone) of the fiber output to prevent energy loss.
The Spherical Biconvex Lens is the gatekeeper of your system's quality; if it fails to collimate effectively, no amount of downstream adjustment can fix the resulting beam.
Summary Table:
| Feature | Function in Dual-Spot System | Impact on Performance |
|---|---|---|
| Primary Role | Beam Collimation | Converts divergent fiber light into a parallel beam |
| Positioning | Fixed at Focal Length | Ensures beam consistency and prevents premature convergence |
| Core Benefit | Spot Shaping Preparation | Enables predictable beam splitting and size adjustment |
| Stability | Geometric Foundation | Maintains energy density and output shape stability |
| Limitation | Spherical Aberration | May cause slight beam 'softness' compared to aspheric types |
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References
- Nicolas Kudsieh, Zachary C. Wiley. Design and fabrication of dual-spot-size medical laser-handle prototype. DOI: 10.1109/honet.2019.8908115
This article is also based on technical information from Belislaser Knowledge Base .
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