Exact focus point of 1600mW laser module diode. SM1

Hello; I am trying to understand what the exact focus point is for the laser beam on the 1600mW laser module diode. The point of focus ought to be a known specification of the 445nm laser diode but I cannot find it referenced in the forum. I believe the matter was discussed once but the search tool is not bringing this subject up for me. Any assistance would be very much appreciated. The number in my recall was around 34mm but I could be imagining that.

@Hauke @Tone @Edwin @JKC20 @Atom

I’ve no idea. Would you mind to explain what you need it for? Btw.: IMHO such a value will have a bit of tolerance - you will not be able to skip focussing procedure… But I may be wrong, not an expert here…

Sure thing. If there is a set focus distance where the laser beam is as convergent as is possible with the diode design, it should be possible to take that number and plumb it in to all of the work so that the step of focussing the beam is no longer required. Furthermore, entering the thickness of the stock should then have the Z height back up by the thickness of the workpiece plus the known focus distance and the need for focussing the laser beam is removed.

It may be easier to explain with a couple of images. The first image is a great example from an ideally focussed laser beam from my 1600mW laser module. The converging beam tells me that there is a specification for that diode that ensures that the designer knew that the focus point had to land somewhere within the specified range. That being the case, I would expect the laser beam to always be in focus at the same point in space. The only reason to make that point different is by inserting a piece of stock in the path of the beam.

It has been my contention from the start that if Luban knew the Z height required to achieve perfect beam focus on the provided table (each module is presumable tested at the factory); all that would be required from the user is to enter the stock thickness of the workpiece. Luban would then adjust the Z height and no focussing would be required. Each module could also have the point of sharpest focus in millimetres engraved onto it. Now the user could make whatever adjustments were required to keep the beam point at maximum sharpness. (more of this later when I demonstrate Lightburn).

As it is, here is the interface for this aspect of Lightburn. The next three images show the some of the Lightburn GUI and the settings which can be made relating to Z height.

The first two permit one to set the Z height as the focus point. I want to design and print a power ramp for each setting adjustment in focus… say every 0.01mm of focus for specific materials. I hope this will prevent scorching or smoke damage. I also want to find out how to use the cut modality and see what gives the best results.

The power can be varied very easily so I will be able to build a library of materials and keep them in Lightburn’s library and just apply them when needed. Each of the tabs provides another pallet and there are three settings pallets including preferences that do not have a pallet on the left. The settings for Z Axis control are accessed for the screwdriver and spanner icon (tools)

I am working on a couple of demonstrations so that I can screencast them on the grounds that one picture is worth a thousand words.

from my experience with lasers, while there is a calculated focal length that is based on “perfect” conditions, the actual focal length with be diffrent and can change based on things like humidity, diode and optics wear, etc.

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Thanks for that Adam. I guess I have no idea how variable the diode focal length can be. I need to research the issue thoroughly. My science says to me that the focal length will not change because it is a function of the construction. If the focal length can be out by say… one millimetre, then the laser diode is useless for scientific work. If the rise in ambient temperature makes the laser diode and its contents expand in some way, it is bound to settle after reaching operating temperature. The working temperature and operating temperature are surely set at the time of manufacture. It is clear that 0.01mm is not madly accurate as these things go. I am hoping to produce a working protocol that will account for focus shift (if such an entity exists in laser diodes) without having to painstakingly jog the Z axis to find the focus point. I would prefer to set the focus point numerically.

Edit Stupid of me. The laser diode focal length is not the most important parameter to consider. It is of course the lens array that is placed in front of the laser beam. So the focus point will be known via the focal length of the lens placed in front of the laser beam. So now it is about the accuracy of the steady state that any operating diode laser beam can work to.

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It can be done but it’s all based on the construction… think of it like a piece of furniture, it will swell and and shrink with heat and moisture, but the largest factor is how well it was built. If it’s built well it will be sturdy and only change a little. If it was built poorly it will have slop and could very by quite a bit.

As far as how they use them for science, when in a lab high power lasers are tightly controlled. Optics are cleaned and set before each use. And the climet in the lab is controlled to reduce humidity and excess heat and debris.

Not sure how industrial laser cutters work, if they use auto focus or simply a numerical offset. Either way what you want to do should be possible, just may not work quite as well as you hope. Good luck and happy making,
-Atom

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I see that now, Adam, thanks for your response. Of course, it may be possible to change the lens as it is possibly/probably a common thread and it could be swapped for a high resolution lens of another focal length. I should ask the question again (plus subsidiary questions) but with a different emphasis. I will go and formulate the question to the forum and see what develops. I believe that the beam width is 0.5mm. I wonder if a different lens will change that. Optical rules suggest that it may.

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@Edwin & @JKC20: Hello; If you have been following this thread, can you confirm for me the details of the threaded lens fitting in the 1600mW laser module. I want to know the actual size of the thread and whether it is a known and widely used standard. My feeling is that it may well be, having seen other laser diode modules.

I have further questions about the focal length of the lens and whether it is denoted as a high resolution lens. If the thread is a known standard, do you know of any work to change the lens for higher resolution? I think the lens array has a dark interior for higher resolution. Can you also tell me the lens construction. How many pieces of glass and in what construction pattern are they and what size is the diameter of the glass?

I am considering swapping the current lens array for another if it is straight fit. I want to see if I can adjust both the focal length and the resolution of the laser beam. Thank you!

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