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Laser diode wavelength choice

Posted by sky99 
Laser diode wavelength choice
January 25, 2018 01:56PM
Hello everyone!
I have an Openbuilds C-beam machine, controlled by an original smoothieboard 5X.

I would like to add a cheap engraving laser diode onto it, to engrave logos on wood/acrylic
(also i'd like to try things on 3D printed objects : see what post processing is possible with a laser.
The prints coming out of my prusa I3 MK2 are great, but i'd like to try new things, texturing, logos, etc).

It would be great to be able to cut stuff, but if i can't, no big deal, i still have the router spindle for that.

I'd sill like to be able to cut vinyl to make stickers, for the rest, engraving only is fine.

So i've been looking around, but i have a hard time figuring stuff out.

First question i have is about laser wavelength. I have seen 445/450 nM lasers, at up to 2.5W in my price range.
But i also saw 405nM lasers, but only 0.5-1.5W, and i have to find the control board.

So the question is : how do i chose laser wavelength?
Does smaller wavelength means more energy, thus more cutting power for the same wattage? or is it irrelevant?
I've read that red laser diodes need much more power to cut trough stuff, but how to factor this in?

What is better between the shorter wavelength with lower power and the higher wavelength but higher price?

I've also read that certain laser wavelength works for certain types of materials, colors, but how to know which is good for what?

Am i over thinking this?
Re: Laser diode wavelength choice
January 26, 2018 03:48AM
Those diode lasers are not suited for acrylic engraving. ( except you have very dark tinted acrylic )
I have had good results with the "blue" lasers at ~445nm. I wouldn't know, how to focus a ray that is partially invisible ( 405nm ).
Re: Laser diode wavelength choice
January 26, 2018 04:17AM
... 405nm is pretty good visible, so no problem to focus. But for better usability you can use 445nm diodes too -- the 405nm have a grater material selection, but lack of power, compared to the 445nm diodes (max 0.5W with the 405nm, up to 3,5W or 6W with 445nm).

But no problem either with totally invisible IR-lasers or UV-lasers if you have an "indicator-card", that lights up when hit by the beam ... or simply by burning a piece of material and measure the distance of the smallest/hottest plasma spot == any laser wavelength, strong enough to burn and evaporate material, will create a visible plasma (fire) in the spot.

For fine adusting the focal distance burn traces with varying distance and compare/measure for the finest trace ...

Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: Laser diode wavelength choice
January 26, 2018 09:37AM
Thanks for your answers, so 445nM rather than 405 for the availability of higher powered lasers.

Thanks for the explainations on the focusing also. I think that i'll first do a raw focusing with the lens, then a fine adjustment with the Z-axis of my CNC smiling smiley

Also, this is just purely for knowledge, since i don't find cheap laser diodes in other wavelengths than 445 and 405 with acceptable power, but :

Considering only the wavelength, no other factors such as price beeing important, what wavelength would engrave clear acrylics? Would it also engrave wood?
What about metals?

is there a wavelength that would be suitable for all purpose lasering stuff?

About some materials being transparant for the lasers :
-is it :

  • each wavelength that has it's transparant material(s) (meaning that each laser wl is suitable for some applications, not for others) , or
  • reducing or increasing the wavelength above or below some value will simply remove materials from the list (as in : laser A with X wavelength will cut/engrave more materials than laser B with X+Y wavelength?) If so, which is it : lowering is better or increasing? (or is it both, the farther from visible the better?)

I hope i'm not beeing anoying here, but i didn't manage to find this information clearly. I thus posted a topic with an explicit title, so that if we can get clear answers (or state that there is no clear answer), other can find the answer here later on smiling smiley

Edited 2 time(s). Last edit at 01/26/2018 09:44AM by sky99.
Re: Laser diode wavelength choice
January 26, 2018 11:09AM
... materials have different transmission values for different wavelegnths - while transparent mterials are transparent for VIS (visible = roughly 400nm to 800nm) and NIR (Near Infra Red = 800 to 1200nm) diodes too, all organic/plastic materials are "perfect black" for CO2-lasers (10600nm) or deep UV lasers (below 300nm).

So for clear acrylic and wood of some millimeters thicknes you'll better use a CO2-laser.

Metal is different - it's highly reflective for CO2-lasers, so you'll need powers of some hundred Watts to get into or through.

But it will absorb in the NIR - so most metal marking/cutting lasers are NdYAG- or fiber-lasers with wavelength of 1064 to 1070nm.

For the VIS diodes it's a matter of power - the 445nm-diodes with 6Watts of power can be used to mark steel ... but for real engraving or cutting you'll need much more power ...

Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: Laser diode wavelength choice
January 30, 2018 09:25AM
Many thanks for all the information, it's been a really good source for better understanding things!
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