Inventables Community Forum

Diode Lasers - Q & A - Focusing, Lens, Cooling, Diodes, Safety, Parameters & others


Since some of you found my first thread valuable I decided to create new thread strictly conected with diode lasers. I'm here and I would like to share some knowledge with you guys. I'm not sure what exactly would you like to know but probably many times you had some questions and maybe there was none who could answer precisely.

I'm mechatronics engineer and I've been working with diode lasers for 7 years. You can ask about everything connected with lasers:
electrical and optical parameters, diodes types, differencies, efficiency, focal distance dependancies, lens types, drivers, feedrates, experiments, safety, cooling, materials and probably many more.

Sometimes I may not answer if the question is connected with the company secret for example "What transistor and op amplifier (symbol) do you use in drivers?"

I will try to answer all questions you ask.

Despite this you can send us a samples of a materials and we can prepare the cutting/engraving tests and then post the results. Remember to add a letter with your email address to send you back the photos with results and also include specyfic name of the material, exact type of plastic etc. For shipping use the address below:

Opt Lasers
Tomorrow's System Sp. z o.o.
Okulickiego 7/9
05-500 Piaseczno
+48 515180752

1. Try to be specyfic in your questions, of course there may be also general questions
2. Drawing is the language of the engineers
3. Be nice :slight_smile:



Great to have you here to answer our questions on lasers. Here's a quick one, why do some lasers (like the K40) use mirrors, and other lasers don't need them?

a K40 is WAY more powerful. The laser comes from a glass tube, which is very fragile and expensive, so best kept away from moving parts. That's why it is usually mounted at the back and the laser beam is redirected through mirrors.
A low-power module probably has some sort of LED as light source, so much more compact and not fragile.

Also, very long, usually water cooled. You would have to have a very large Z axis to use the beam directly.

Laser diodes are usually lower power. Each of these things reduce the optical power, reflections, material transitions (lenses), length of optical path, and others.

We did some time ago a CNC router with the glass tube mounted on the spindle. It is a big machine so it was not a problem. But most of the answers you already have from @LarryM and @xfredericox. I would add here also some other points:

  1. Diode lasers are small and there is no need to make the weigth of the moving part smaller, so usually it is just mounted on the moving part.
  2. Beam profile - as the CO2 laser have really nice round beam with quite small divergence in the diode lasers in order to obtain higher power you need to use lens with high NA (numerical aperture) so for example G2 lens. Nevertheless this kind of lens are producing the beam with very bad divergence, for example around 6mrad. This kind of beam at 5 meter distance has 25mm size! This means that to focus the beam you will need the lens with diameter of 25mm. The longer the distance the bigger the beamspot. This kind of lens are not easily available since there are mostly two types of lens (cheap ones) one are 25mm for CO2 and second one are 5-10mm for diode lasers. So just for long distance it is hard to produce cheap mirror + focusing lens setup. Anyway with such machine as X-Carve it is possible since maximum length will be around 2,5 meters. There will be small problem with cutting because of the light cone angle but it is possible to make such a setup.


What is the margin of error when focusing a diode laser? In other words, how far off the ideal focus distance would a laser have to move to see degradation of quality? I'm asking because I'm wondering if something that was, say, .020" bowed/warped/out-of-flat would affect the quality.

This is tricky question :slight_smile: If I understood correctly you speek about focus depth.

There are equations which allows to calculate it but they are not very simple.
In optics and especially laser science, the Rayleigh length or Rayleigh range is the distance along the propagation direction of a beam from the waist to the place where the area of the cross section is doubled.
Here you can find some equations:

When you focus the beam at 100mm then focus depth will be longer than when focusing the beam at 30mm distance.
Here are our measurements.

Beam was focused at 100mm with beamsot size around 0,5mm.
Each line differs by 1mm in Z distance.
Each dot differs by 0,1mm in Z distance.

As you can see the smallest dot do not change with Z change in around 1,5 - 2mm. To obtain square dot Z can not change by more than +-0,5mm. Anyway this is also effect of burning because even with 0,1 beam spot you can make a burnout which is 0,2mm. With special equipment you will be able to measure it more acurrately but for engraving and cutting it is not that important as you see.

The measurements we did are for long focus and big beamspot (just to see it better). Anyway you asked about 0,02" which is close to 0,5mm so exactly the size of the beamspot you see on the picture.

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True, special mirrors give the reflectance efficiency at >99,8% so the looses are not big because of the reflections. Mostly the looses are caused by dirt on the mirror surface and dust in the air. Of course it depands how the whole optical system is protected. Something very important is smoke and it reduces the power really significantly, this is why using the K40 or other lasers similar type, important is to provide strong airflow.

We did some measurements using stronger and weaker fan and even though the laser could work with 30 40 or 50 degrees there was a difference in power and the power drop caused by the smoke. At start we thought it is only temperature problem but then we found out that weak fan is not removing the smoke fast enough so then the power is not constant when you measure it accurately.

ok I can get a 75watt culminated diode block connected to fiber and focusing assembly would you know what to use to power it and control it with a arduino via pwm

Welcome back.
I know very little about lasers, but it definitely captures my interest.
I still have much to learn about the CNC machining process itself but hope to eventually move into a laser.
I will be sitting back reading and (hopefully) learning.

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Yes, It would need proper laser diode driver connected with some kind of DAC. So basically it is simple thing.

What kind of fiber it is? Basically diodes focused into the fiber are not very usefull in cutting. For engraving they are so so but if you mentioned 75W it is probably an infrared diode so problem is the colour of the surface.

Do all makers of safety glasses provide this type of information on their products?

I think that the makers have such graph but they do not always share it. They can test the goggles in laboratory but all the resellers need is the OD parameter for the wavelength range. For example we have CE goggles and I know they are OD7 for 190-540nm but I do not have this kind of graph. This graph is much more common for dichros and of course filters.


What I'm finding is that, for those that produce this graph, many of the goggles are too close to the transmission portion of the graph for 445nm.

It is my understanding that the wavelength of the emitted light from a laser varies with the temperature of the diode. If that shift is significant then the goggles might not protect as well as one thinks.

These are rated to 450nm:

First ones look much better for 450nm. The change over the temperature is small, around 0,2nm/*C. So even changing the temperature by 50 degrees chnges the wavelength by 10nm (theoretically). It is not much and on your graph, even 470nm looks good:

Additionally when you want to work with blue lasers only then you should try the googles dedicated for blue so the wavelength range will be up to 540nm for example. Second graph you showed me looks like it is dedicated for 1064nm so the colour of the glass/plastic is usually orange/green what is automatically blocking the 450nm also.

Ok, so I guess that if the goggles that one is considering don't have a similar graph to look at, then the best plan is to get ones that are certified.

Would you suggest that?

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Forgot to ask about harmonics. The first set of goggles are better by far, but they don't block harmonics at the upper end.

Is that a concern?

Rahter not, not in such small powers. Maybe some high power YAG laser can produce lot of light with different wavelength but just the 6W blue for example is not able to produce near infrared or infrared just from heating the material up.

About certification even if the graph is given the certification is something different what protection goggles should have. It is even stated in our EU directives. In USA I'm pretty sure that FDA is even more strict about this. Graph is something you can create (in paint :D) and CE mark is something you can't add easily.

Here is the example:

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@Opt_Lasers Probably a little late to the party since the thread is already aging like wine but since I’ve only just recently received my PLH3D-6W-XF I was wondering if I might still be able to get an Answer out of this thread.

As I’m slowly starting to warm up towards my PLH3D-6W-XF I was wondering what part of the Laser exactly being the cause for the safety glasses as I might approach additional safety measurements differently.

Q: Is it “just” the flash at the contact making area or is the entire Laser beam as it leaves the lens until it makes contact already a threat?

For the Laser I planned to use a similar design approach to how I’ve used a clear acrylic blast shield for my milling operations - Just with a 450nm rated protection window featuring a large enough hole for the Laser to pass through and another for the vacuum to remove the smoke.

That design though would only protect against anything happening after the beam passed through the 450nm hole, like the contact flash, but nothing before, like the majority of the beam - Hence my question.

Totally an inadequate and dangerous design idea. Please leave your laser unpowered until you learn more about proper safety precautions. It is good you are asking now. Hopefully the Opt Laser folks will help you with a safe design for shielding their equipment as well as give you other knowledge and instructions you need to operate their lasers safely.

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The whole beam is dangerous, including rays that can’t bee seen.

ALWAYS wear eye protection at the very least and as John already mention I strongly agree you should do some research before just fooling around with it. One split second is all it takes.


I would encourage you to view this safety material. It will give you some ideas for using your laser safely.