Lens swap on Laser Diode modules


On my journey through laser engraving and cutting adventures I got to the point where I would like to know and explore how practical to pursue better optics (lens) for given laser diode.

It is obvious that precision of burning and cutting and specific temperature at the light spot are functions of not only power but also how good light is focused.

With few modules I got - all got very different looking spot: One is square, one is looking like Gaussian spot and one does not focus better than 1:3 oval, though spot still small. All appeared to produce responsible burn, but I can imagine that with tight spot - results can be improved, temperature raised, ceramic fused, TiO2 crystallized to darker chunks and so on.

I focus with USB microscope, at max illumination and max zoom, to reduce blooming. Generally I zoon till spot is between 1/2 an 1/3 of the screed vertical resolution. I’m not relying on my eyes, though I can say that when I check my eye focusing - it is pretty close to one with microscope.

Laser modules themself have very different specs for the spot, if specified at all.

Here is interesting info about laser lenses, and some are matching descriptions on Amazon.

Now I’m trying to find some replacement lenses from Amazon and most if not all appeared to be specified to have M9x0.5 thread. Modules I have are M10 and M12 (I suspect both are x0.5mm step).

The questions are:

What is the reasonable spot size?
Is it reasonable to pursue smaller spot?
How far (smaller) it can be improved? Practically.
What is the common thread size? What are the range of threads?
Is there a good source for replacement lenses? If Amazon - what item number(s)?
It appeared that higher power lenses are fixed focus. Why?
Many specified for distance of 20-23mm. I can imagine keeping lens farther will keep it cleaner longer. IR lasers are essentially are straight beams, I think. So Why optimal is less than 1"?

Anybody got improved results by replacing the lens?

I have a limited amount of experience with different lens types. I haven’t changed lasers since the last module I received was fixed focus.

Don’t have a good answer for this. I think this is mostly dependent on the actual diode array. The manufacturer will list their nominal dot size. From what I’ve seen those numbers are best case with typical values 2x what’s listed.

From what I saw different lenses didn’t so much change the size of the spot as it changed the focus column. In my case I went from a G2 lens to a G8 lens specifically because I wanted better cutting performance. It provided a much longer in-focus-ish column of light than the G2 lens.

I’m not familiar with the range of threads but all of the ones I saw were in the same M9x0.5 category that you saw.

This was a few years ago but there were a couple of well regarded ebay sellers that I was referred to: barnett_unlimited and dtr-lpf. I can’t recall which one I purchased from but the experience was uneventful. Got what I expected in the time that I expected.

I can’t say for certain but I suspect this is partly to reduce user error and to reduce variables. It’s a lot easier to just have a user use a measuring column of tool attached to the laser module to set a fixed distance to the work material then it is to instruct someone how tofocus a laser. There’s a safety element to this as well as people were probably burning out their retinas. The fact that CO2 lasers often work this way probably also contributed to the notion of wanting to work like industrial lasers. i would say all in this was probably the right decision.

I can definitely say for my purposes of deeper cutting that it made a tremendous difference. It did not help specifically for narrowing focus but I wasn’t expecting that either.

IMHO, type of laser should not matter when it comes to lenses… it’s the same game. There are a number of videos of K40 users sticking their finger in the beam before the lens, resulting in a minor type of burn like a cigarette.

What makes the laser is the lens, just like a magnifying glass the lens makes puts all the energy across the beam into one, hopefully, small spot.

Little difference between the ir and visible when it comes to lenses.

Don’t know what you mean by a ‘high power’ lens, they only come in varying focal lengths that I know of. If you’re talking about focal length… I’m on board.

I have a co2 and have a 1.5", 2", 4" and a compound lens. I don’t know the compounds focal length, but it’s shorter than any of the others. I use the 2" and the compound most and the 4" for cutting thicker material…

Generally a long lens, like a telephoto will have a large ‘depth of field’ meaning it will stay in focus for a longer distance… the tradeoff being it’s not as ‘crisp’ as a shorter lens.

The compound is used for the smallest dot I can make… Somewhere around 0.05mm following Russ Sadler observations/computations. Generally I’m happy with the 0.10 size I can easily get with the compound and usually the 1.5"

If your material isn’t absolutely flat, then the compound will go ‘out of focus’ with a minor change in distance. It won’t been seen with the 4" lens, as it’s focus range is much larger, but not as small of a focal point.

I’ve been asking about the size of the output ‘dot’ ever since I started looking at lasers… My 30 watt Neje specifications

Notice it’s missing… here is the 40 watt dual diode model

I’ve seen advertised values of of ‘dot’ size from 0.10 to 0.05 from the different manufacturers… it’s reasonable to assume if you can put 10 watts down in a 0.10 dot, then you have 20 watts if you make the ‘dot’ half the size… ?

You can see what they are doing, but you don’t gain power by making it smaller. Just the area with the same wattage if half of what it was… it has the ‘effect’ of what they call an increase in power…
This follows the math that if you can make if small enough then you can have the power of the sun… at least that’s what they want you to believe.

You can chase the ever smaller dot, but at some point it’s too expensive for such a small gain… I think anything less than 0.10 (254dpi) is probably good, if you can get one half that, 508 dpi, then it would give you better resolution… depending on the material.

Keep in mind that they always advertise much larger than they deliver. The 40 watt module is a good example. It draws 40 watts and runs two diodes, each diode drawing 20 watts. Both of these diodes go through a beam combiner (lost power) and a lens, again, lost power… They claim an output of 10 watts +, so the efficiency of the system has to be at least 25%… I think that is very generous.

I’ve seen the hand picked, temperature, voltage and current controlled led for a 90% efficiency. That is by far more than we can expect.

My co2 lps states >90% efficiency, that would be at a voltage/current of your tube, so the system has a >90% efficiency as the tube is lasing at it’s maximum power.

Mine is set to focus at 30mm and they data says it will go to 50mm… I can slide mine up and down on it’s mount, so it’s like the co2, just slide it down to the spacer and lock it.

All lasers are that way… coherent energy source…

I’m running out of gas for the night… Take care