# Alternatives to laser line?

I'm trying to project a very thin line at a low angle over some surface defects (peaks and troughs). The scale is ~20mm square, but the defects can be sub-mm (0.2 - 1.0mm).

I am currently using a line generated by a laser pointer. The $4 laser diodes work well enough, but the line spreads out due to the low angle and poor focus(?). Are there any better / safer alternatives, such as some LEDs + lens that could also focus the light into a line? I'm new to engineering and optics so any advice would be much appreciated. • You might go to the hardware store and buy a laser line/level tool. They're cheap and can produce either a line or a swept line in a plane. Jun 21, 2021 at 12:47 • What about an interference plate and monochromatic light source? Jun 22, 2021 at 22:33 • This sounds very interesting - how does it project a line? I've had a look on Google, but I don't understand. Thanks! – John Jun 23, 2021 at 9:17 ## 1 Answer A few points that don't fit into a comment but could help you: • Get a better laser source than a 4 \$ laser diode. "Better" means a laser with higher beam quality. When you look at a laser's data sheet, it should specify a value $$M^2$$ or "BPP" (beam parameter product). Both these numbers are related, the smaller they are, the better you can focus the laser beam.
• Use a cylindrical lens (if you don't already), they are meant exactly for your application, focusing a laser onto a line instead of onto a spot.
• From how laser diodes are built, compared to other laser sources, their beam quality differs in the two lateral directions. That means, a diode laser beam diverges for example faster in its height than in its width. It's only an assumption derived from this, but rotating the diode by 90 degree around the beam axis could possibly improve the focus of the laser line in this particular application.

I think that with a laser you are already on a better way than with an LED, it's just about a few tweaks to improve your laser line.