What is Powell Lens?
Powell lens is a prism with a rounded roof which used to transform a laser beam into a straight, uniform line. It's not a standard lens that focuses on light, but rather one that creates a highly precise line of light.
How Does Powell Lens Work
It takes a single point of light from a laser and spreads it out into a straight line.
Creating the line: As the laser beam passes through the lens's apex, the surface geometry splits the beam and spreads the light into a "fan" of uniform intensity.
Compare with Cylindrical Lens
Unlike a simple cylindrical lens, which can create "hot spots" (areas of higher intensity) in the line, Powell lens produces a line with very even brightness and thickness.
Key Specifications
Fan Angle (θ)
The total angle of the laser line coming out of the lens. This angle tells you how wide an angle the original beam is fanned out over. It is fully determined by the roof angle of the Powell lens and the index of refraction of the material.
How to Calculate the Laser Line Length
The formula for the projected line length of a line-laser with fan angle θ at a working distance WD is:
L ≈ 2 · WD · tan(θ/2)
Where:
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L is the length of the projected laser line on the target .
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WD is the working distance from the laser to the target.
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θ is the full fan/opening angle of the laser (in degrees or radians).
Input Beam size
Powell lens are only suitable for incident beams of the corresponding size. When the input beam size is too large , the relative intensity at the ends of the projected line increases. When the input beam is too small, the line’s longitudinal intensity profile tends toward a Gaussian.
Line uniformity
Line uniformity measures how consistent the brightness is along the whole laser line.
The formula for the intensity non-uniformity of a Powell-lens laser line is:
Where:
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U is the intensity non-uniformity in percent
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Imax is the highest local intensity along the usable part of the line.
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Imin is the lowest local intensity along the usable part of the line.
Note: In practice, the uniformity area is around central 80%-90% of the line
Choosing Powell Lens
Laser Wavelength: The lens material and coating needs to be fitting your laser's wavelength.
*Normally, it will be N-BK7 and Uncoated
Input Beam Diameter: The input beam diameter should not exceed the Powell lens design.
*Usually ranging from 0.8mm - 5mm
Fan Angle (θ):
*Usually ranging from 30° / 45° / 60° / 75°. Smaller or Larger Fan Angle can be customized
How to Mount a Powell Lens
Self-Centering Mounts
A self-centering mount uses spring-loaded jaws to automatically grip the lens by its edge, ensuring its optical axis is precisely aligned with the mount's mechanical center.
Tube Mount
Powell lenses can also be fixed into a tube mount. (by using UV Glue)
Applications
Machine Vision: Powell lenses are widely used in machine vision applications, such as product defect detection, dimension measurement, and alignment.
Flow Cytometry: Powell lenses are used in flow cytometry instruments to measure the size and shape of cells and particles.
Laser Printing: Powell lenses are used in laser printers to produce high-quality barcodes and other markings.
Optical Measurement: Powell lenses are used in optical measurement instruments to measure the smoothness and roughness of surfaces.
Takeaway
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Use a Powell lens when you need a bright, straight, and uniformly illuminated line from a laser.
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The line it generates has uniform intensity along its length, which provides even illumination throughout a system.
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Powell lenses are available with different fan angles.
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