That is true. I made an argon laser with dichronic mirrors before. Looking straight at the mirror, it was much brighter than a normal mirror. If you tilt it to the side, you could see right through it, with a color that changed from yellow to magenta. Very strange indeed.
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@Ante_Vukorepa and @Bruce_Boone - I think youâre missing the point. Before my Form1+ I actually replaced my galvos because the machine was out of warranty and theyâd gone haywire (it worked - all documented in old thread) so Iâve seen 4 galvo mirrors up close, Iâve also looked at the galvo mirrors in my new form1+ and none of the 6 looked like that - they all had perfectly mirrored surfaces.
It seems blindingly obvious that a mirror like that will cause problems - most especially interesting is to see the new characteristic ârabbit earsâ.
I wonder then if this is the cause of ârabbit earsâ, and itâs not the laser as folks first assumed - which might explain why FL have had difficulty reproducing this, and maybe why @Ralph_Roberts machine was ârepairedâ and yet still exhibited the issueâŠ
Oh - and @RocusHalbasch - fantastic job with the pics.
If itâs a metalized mirror and you can see through it, that is definitely not right. If itâs a dielectric one, it could be possible to look like that and still reflect 98% of itâs intended wavelength. It seems more likely to be a normal metalized one, which would be cheaper to produce and being that the other one looks fully reflective from the photo angle. The question is, if it is that noticeable now, was it like that when the unit was assembled and tested, or is that something that happened after the fact. It seems that a see through mirror would easily get noticed by the assembler. Such a thin coating of metal wouldnât take much to chemically eat it away, so it might be possible that some adhesive or the resin fumes or something else might eat it. A mirror that leaks light through it could definitely cause a pattern like rabbit ears just due to the internal reflections.
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From your pictures, it looks like you have one regular and one dielectric galvo mirror, which isnât a cause for alarm in and of itself. The dielectric mirror does a fine job reflecting the laserâs wavelength, which is all that matters.
Print failures are a separate matter, and you should definitely open a support ticket if you havenât already â our team will take good care of you.
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@MattKeeter - so you are confirming that FL are using two different types of galvos, and are mixing them in printers?
@MattKeeter I do have a ticket open. However my service person did not seem to know you used transparent mirrors. He asked for pictures and didnât seem to think it should be transparent. However if you guys use both types of mirrors you should let your service people know.
Also is there any reason you guys donât use only one type of mirror? I would think there would likely be a cost difference.
Lastly if the galvo mirror is ok. And all my mirrors are spotless which they are. Does that mean my brand new laser is bad? The flare is coming from somewhere and it is definitely the source of my print problems.
Iâll chat with the support team to clear up the confusion about dielectric mirrors, and theyâll keep up the dialog with you to help diagnose your print problems.
Again, the mismatch isnât a cause for concern in and of itself â both types of mirror should have high reflectivity at our laserâs wavelength.
So itâs just a different style mirror. It sure looked like it missed the electroplating bath. Thanks for clearing it up @MattKeeter. I wish staff frequented posts like this more often.
IMHO â Wouldnât cleaning be nearly impossible with transparent mirrors? Sounds like youâre making mirror maintenance harder fro us if you start putting in transparent mirrors.
The only issue I see with a dielectric mirror is that they are very precisely tuned to a specific wavelength. The resins are not quite as finely tuned. In theory, the laser only puts out a very specific wavelength, but being that we can see the beam, itâs obviously not all ultraviolet in a single wavelength. In the case with the rabbit ears, some wavelengths very similar to the target wavelength might get internally reflected and that could kick the resin. That could easily explain the issue. Going to a full silvered mirror would solve that.
If i were Formlabs, making the second galvo a dichroic mirror is precisely what i would do after switching to a higher powered laser. So yes, that setup makes perfect sense and is not a cause for alarm.
See, blue and violet lasers above 100mW in output are often of a DPSS type - they use frequency doubling, i.e. they use a (deep) infrared laser to pump a crystal which then doubles the frequency (i.e. shortens the wavelength) to blue or violet.
One consequence of doing that is that the laser also outputs a hefty percentage of its power at the original, infrared wavelength. I certainly wouldnât want to be blasting that VAT with unnecessary IR photons (PDMS and heating up, remember?), so a dichroic mirror would be a perfect fit - it reflects the violet and passes through the infrared.
Remember - just because it doesnât look like a mirror to you does not mean itâs not a mirror to the laser.
Of course, that doesnât preclude the possibility of it being a bad mirror. In fact, itâs much harder and more expensive to make a quality dichroic (dielectric) mirror than a regular, silvered one.
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Thanks Ante. Youâre people skills could use some work, but you know more about lasers than I do. So this new info means that thanks to the new style mirror, our resin tanks should go much longer without clouding.
I apologise for my communication skills (or lack thereof).
I often end up sounding grouchy and/or arrogant when not intending to.
Especially before my first coffee 
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No worries. Thanks again.
Thanks for explaining why they would use the two different mirrors. So if itâs not the mirror itâs the laser. I know they have to.d people the rabbit ears arenât a problem but being as in my case the direction of the flare is the side of my rook sample print that comes out raggy and rough I think they are just wrong.
I did some research (well, googling) just now and it turns out 405nm DPSS lasers arenât very common. And most of them are 200mW and up. So the IR blocking hypothesis does not seem too likely after all (although iâm sure there are other reasons why youâd want use a dichroic mirror - not an expert).
Regarding the flare / rabbit ears - those usually occur due to internal reflections.
Either in the laser itself (focusing lens or an iris out of alignment) or something else in the optical path.
This is most likely happening due to internal reflections from the various lenses inside the laser barrel.
The ârabbit earsâ almost looks like a reflection off the inside of the laserâs barrel. Also there is a little spot on mine, so itâs possible that the laser beam is not perfectly aligned inside the casing and is hitting the barrel causing the artifacts.
@Monger_Designs, Isnât that little spot a reflection off the top of the hood back down to the top of the paper?
I donât think so. It wouldnt be that focused.
@Monger_Designs how are your prints? perhaps we can lend some weight to FLs assertion the rabbit ears are not usually an issueâŠ