A response to Sam_Jacoby

Retracted, due to incomplete understanding of Kevin Holmes photograph at the time.

Not quite, the green-circled part in your photograph is not a lens; it is a substrate on which the laser diode is mounted, a rectangular block of silicon, or SiC, or diamond to carry heat to the heat-sink slug. See illustration at http://en.wikipedia.org/wiki/File:Laser_diode_with_the_case_and_window_removed-powered_off.jpg for a view inside a lower power diode laser - in that photograph the laser diode is the small black wired die, the silvery covered block is the thermal mount which carries heat to the gold-plated thermal slug. In your photograph, the diode is the thin rectangular item to the upper left which your green line runs through, and in a perpendicular view is centered within the optical window.

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@Ishmael_Stefanov_Wag nope - take a look for yourself if you have an F1+ - obviously my photos are not good enough, it appears you’ve fallen prey to the same confusion as @Ante_Vukorepa - he couldn’t see for himself yet because his F1+ has yet to arrive.

It seems it’s not as clear on the photos as I’d like apparently - but look at the specular reflections of the USB microscope lamp in the other photo above - that might help you see the cylindrical curvature.

I guess I’ll see if I can take a video and if that will be clearer - but let me assure you the green circled object is a cylindrical lens, and it’s logically impossible for it to be anything other than a lens- because as I’ve stated at least twice before - it’s the last thing in the path of the light beam before it exits the laser barrel

Take a minute and think about that - if it was not a lens, and it was the substrate of the laser diode (it’s far too large for that by the way, the width of that green oblong is about 6mm) then there would be no lenses at all in the F1+ laser - which is just not possible. Note that as I’ve also stated several times before - the F1+ laser has nothing mounted in the laser barrel thread.

Its all very easy to confirm for yourself if you have an F1+

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I will accept your premise, since you have the benefit of manipulating the microscope to better view the inside of the laser assembly.That lens can correct the inherent astigmatism and focus the beam at 30cm, which greatly simplifies their optical assembly, and makes it more difficult for us to find a drop-in replacement. A previous note indicated that the near beam profile is rectangular, rather than elliptical, which would indicate vignetting in the optical system. And if those vignetting elements are at all reflective, could very well be the source of the flare.

Actually, an unfocused diode beam is usually rectangular.
It’s vignetting (by an iris and/or a lens system) that usually makes it elliptical.

5mW visible laser diode at normal incidence to matte white paper. No optics except the window. Ends of beam vignetted by package. Otherwise, looks elliptical to me, like other unprocessed (visible) diode laser beams. Or in this graphic from http://www1017.vu.lt/

For most of them i’ve seen it’s more of a truncated ellipsoid (truncated on the long sides) or a rectangle with gausoid on the short sides. Something like this:

(Ignore the circular edge, that part is clearly vignetting.)

I guess it depends on the size of the diode can’s window and distance from the die.
I’ve never seen a naked die’s beam.

Anyway, re: Form1+ laser - if it is elliptical and is made rectangular by something in the optical path, then it’s likely the cylindrical lens, as its cut is rectangular and seems (at least as can be discerned from the photos) to be terminated by other material on all sides.

Could this maybe get it’s own thread?

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So if the beam is elliptical in the first place and corrected by lenses then why is the flair usually start from the center and to to one side and not flair out in 2 directions?

Yeah, that’s what i’ve asked a few posts upstream.
It could be due to lense not being centered over the diode, or due to different material surrounding the lenses on different sides.

@Ante_Vukorepa that’s my theory too - that the cylindrical lens is not centred over the diode - or at least it’s not centred over the beam from the previous lens.

It matches with a couple of prime observations - First the beam itself is bent to the side matching the bad flare - it’s not concentric with the laser barrel - when you rotate the laser, the spot transcribes a circle.

Second I’ve used a concave lens to diverge/enlarge the beam profile - (and a convex to re-converge it) then cut off a fraction of the magnified profile on the side opposite the bright flare - and the bright flare vanished at the focal point - just as if the cylindrical lens was slightly skewed to the bright flare side, hence exposing the opposite beam profile to a higher angle of incidence in the lens, and bending the light too much.

Also - but perhaps more circumstantial - the sides of the cylindrical lens are clearly visible - with nothing against them - seemingly leaving its position aligned properly orthogonal (as it’s flat against the brass faces behind it) - but it looks as though its horizontal position is not constrained when its placed.

If those observations do in fact match to an off-centre lens, then there’s a very simple, very fast test to see how bad your laser is - do the spot test, mark its position, rotate the laser 180 deg, do the spot test again - mark that position and then measure the distance between the marks.

This will give you an indication of how much your beam is bent off centre and hence potentially how off centre the cylindrical lens is.

This is why I raised the other thread asking FL to dismiss the FUD around voiding warranties - since the proof of the pudding would be someone with a good laser measuring their 180deg rotated spot distance.

I’ll be making another thread on just this topic with pics etc at some point - but in the middle of printing at the moment.

PS - I think the rabbit ears are something else - possibly reflections - since the bright flare (the carrot) can occur on the same side or the opposite side to the rabbit ears and it was unaffected in my experiment above.


I stumbled across this post on the internet, and I just wanted to offer some insight into the problem.

Based on what I’ve read in the post, the two cylindrical lenses indeed are there to circularize the beam from the laser diode. There must also be a collimator for the laser diode directly attached to the laser to collimate the spatially incoherent laser diode beam, and there should be another doublet lens to focus it to a narrow waist.

Having said that, there are two potential problems here. (1) Laser beam is misaligned. Correct optical alignment is crucial for optimal performance. Rings or blurry edges are indicative of misalignment. (2) There is no scan field correction. An off-axis-defected beam from the galvanometers would generate abberated images in a curved plane as opposed to a more desirable flat surface. This makes the laser beam cross section ellipsoidal away from the center.

For the former, you could probably align the laser yourself or just get rid of the cylindrical lenses and add a pinhole, as someone may have done. (But watch out for the power requirements for photopolymerization).

But the latter is not trivial. An obvious solution would be to put a scan lens. However, the scan lenses are special set of lenses with different materials and properties and cost hundreds of dollars at least. (If you do go with this option, I’d suggest you take eyepieces from used microscopes on ebay and run them in reverse as scan lenses to cut down on the costs.)

Alternatively, one possible inexpensive solution may be to construct a 4f system by buying an appropriate doublet to accompany the existing one and putting an aperture in the Fourier plane to minimize geometric abberations. I’m not sure whether this approach would work (people typically don’t worry about laser quality in optical research) but it’s worth a shot.

I hope some of this information helps. I don’t have the Form 1+, but I do related research and found the discussion here interesting.


I have a question, right now if I print something flat the surface is perfectly smooth with no patterns.
I have a flair on mine but doesn’t seem to be causing any problems.

If the beam is corrected and the end size is changed at all will that cause a pattern?

On my laser engraver If I try to burn a large surface area you will notice a halftone pattern because the laser spot is round and as it burns you will have an overlap causing small ellipses of extra burn. Just the nature of the beast.

@KenCitron my old Form1 printers that didn’t have these problems had a notable texture comprised of parallel diagonal lines on flat surfaces that where parallel to the printing plane. Each of the three had different degrees of this texture which I assume was directly related to how well focused the beam was. One of them the texture was strong enough so if you ran a fingernail across the surface perpendicular to the lines it made a nice scratchy sound like one of those pictures that looks 3D without glasses, or one of the ones where it moves as you move your head side to side.

extremely informative and interesting - thanks for teaching!

The periodic line artifacts often arise from vibrations in optical systems. In this case, a fan on the same table may be the culprit. If you suspect another machine may be causing vibrations, you could move the printer to a different, more stable platform or purchase a vibration dampener, such as a tool liner, which you can obtain inexpensively.

Another source may be inherent vibrations in the galvanometer. These vibrations can be quite large, especially at certain frequencies (i.e. printing speeds) near the resonant frequency. It could sometimes be remedied by tightening the hold on the galvanometers. But sometimes, it is impossible to fix (especially if using budget galvanometers) and must be tuned using a Fourier filter. (On the same note, in much rarer cases, the artifacts may be the result of noise in the Fourier plane.)

And as a general response to others’ printing problems, if there are printing errors despite having a good optical system, it is probably related to the resin. Try a new resin and see if you have the same issue. I’m sure it must be documented somewhere, but resins should not be exposed to sunlight or oxygen or heat. Ideally, it should be capped tightly (perhaps using some teflon tape or plastic film around the cap) and stored in a dark refrigerator (not with food).

Which periodic line artifacts are you referring to?

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