Cylindrical Lenses for Laser Line Shaping: A Guide
By Esco Optics, Inc. | Published: 2026-10-20
Category: How-to Guides
Learn how cylindrical lenses turn a laser beam into a focused line. This guide covers substrate choice, focal length, and alignment for line shaping.
Quick answer
Shape a laser into a line by placing a cylindrical lens so its curved axis focuses one direction while the flat axis passes the beam unchanged. Choose fused silica for high-power or UV sources and N-BK7 for visible and near-IR work where cost matters more.
Why a cylindrical lens shapes a line instead of a spot
A cylindrical lens focuses light in only one direction because its curved surface is shaped like a cylinder, not a sphere. The result is a focal line that runs parallel to the cylindrical axis rather than a point. This is exactly what makes it useful for laser line shaping: one axis gets compressed or expanded while the other stays unchanged.
The practical trade-off is orientation. Rotate the lens and the line rotates with it, so the cylindrical axis must be aligned to the direction you want to keep unmodified. This is the most common setup error, and it shows up as an asymmetric or tilted line instead of a clean stripe.
Steps to shape a laser line with a cylindrical lens
- Confirm the laser wavelength and substrate: Check your laser wavelength and power density first. Fused silica handles UV and high-power sources; N-BK7 is fine for visible and near-IR work at moderate power. A common mistake is assuming every cylindrical lens works across all wavelengths. Match substrate to wavelength before you order.
- Pick the diameter and focal length: Choose a diameter larger than the beam's 1/e² width so the full beam passes without clipping. Select a focal length that places the focal line at the working distance your application needs. Shorter focal lengths produce a tighter line but require more precise alignment. Check the beam size at the lens position, not just at the source.
- Orient the cylindrical axis correctly: The curved surface focuses one axis only, producing a focal line parallel to the cylindrical axis. Rotate the lens so the axis matches the direction you want to compress or expand. A 90-degree rotation swaps the focused and unfocused axes. Mark the cylindrical axis on the mount so orientation is visible during assembly.
- Align the input beam to the lens: Keep the beam centered on the lens aperture and parallel to the optical axis. Tilt errors turn the focal line into a blurred ellipse and reduce the usable working distance. Check the reflected spot position to confirm the lens is square to the beam.
- Choose substrate by wavelength and power: For UV work or high-power beams, pick a fused silica cylindrical lens; for visible or lower-power lab setups, an N-BK7 cylindrical lens is usually enough and more budget-friendly. Match the substrate to your wavelength before ordering, not after.
- Verify the focal line orientation: The focal line lies parallel to the cylindrical axis. Rotate the lens so the focal line matches the direction of the line you want to create, then lock the mount and check the line width at the working distance. Mark the cylindrical axis on the mount so rotation is repeatable between sessions.
- Confirm diameter and focal length before ordering: Cylindrical lenses come in diameter and focal length options. Choose a diameter that fits your mount and a focal length that matches the working distance of your optical layout. Verify the clear aperture is larger than your beam diameter to avoid clipping.
Lenses mentioned in this guide
- Cylindrical Lenses, S1-UV Grade Fused Silica: The curved surface of a cylindrical lens is shaped like a cylinder, and its performance is characterized by a focal line parallel to the cylindrical axis. This focal line behavior is exactly what turns a round laser beam into a thin, uniform line for shaping applications.
Cylindrical Lenses, S1-UV Grade Fused Silica - Cylindrical Lenses, N-BK7 Optical Glass*: This N-BK7 cylindrical lens offers a lower-cost entry point for prototyping and visible-light setups. It lets you validate a line-shaping design before committing to a more expensive fused silica optic.
Cylindrical Lenses, N-BK7 Optical Glass*
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