Scanner Mirror Modification

[planters]

Nice find Steve; not geese,but gold. If Macona wants to tackle this then I'll do what I can to help him. If not, then this looks like a good route. This looks like more and more like as it should be; lasers serving lasers and the the Dremel might just have to sit this out.

Now, if precision is within reach then I think I had better analyze this more deliberately. I am going to see if I can get some help doing a FEA of the bending and resonance of these mirrors and the mods

[mixedgas]

Potomac started out making tiny tabletop Excimers for drilling. They then found out there was a huge market for precision drilling but no one wanted to develop the needed expertise. They found their place in the market.

I've refered my past employers to Potomac twice. Both times the projects were taken out of my hands, made secret, and I never saw the results.

Whatever I can do to help Macona as well, ie x-y table stuff, controls, motor stuff etc.

Steve

[macona]

I suppose it is worth a try, ought to be able to program a raster and carve out some glass. I really need to pick up one of the chinese laser cutter controllers. They will handle raster engraving which would make the job a lot easier.

I guess I need to find some glass samples. What kind of glass are the mirrors made from, something like BK7 or more generic soda-lime?

I do have a Vulcan furnace that has a 30 step programmable control that could be used for annealing as well. Like this but I installed a new control: http://www.gesswein.com/p-1622-ney-vulcan-furnaces.aspx

[planters]

I guess I need to find some glass samples. What kind of glass are the mirrors made from, something like BK7 or more generic soda-lime?

I heard that EM is "GOING TO" fused silica ostensibly because it is stronger. I believe microscope slides are soda lime. Edmond optics has 1 wave Borofloat for $15 with "three times the thermal shock resistance". I suspect that if you can get the microscope slides to work, everything else will.

I would not try to anneal these mirrors because aside from the likely coating damage, the stresses you might relieve may cause the surface figure to change. This has not been discussed before, but aside from the coating performance there is little or no evaluation of the surface figure of these scanner mirrors. I have some of the large 14mm wide EM mirrors and they introduce a small amount of negative power which requires all the lasers to be final focused THROUGH the scanner. The advantage of this post processing/polishing is to take stock mirrors and lighten them. In fact if a jig can be worked out then maybe you don't even remove them from the galvos.

[mixedgas]

Anecdotal info:

High school cheap slides might still be soda line. The better stuff from University vendors is some form of doped glass with a bit higher melting point and higher hardness. It still has a COE of 88 when I fused it, which means its still some form of soft glass. I had to fuse two pieces of the good stuff a few weeks ago, and it was not butter soft like soda lime, once melted. Soda lime is greenish in transmission if you view a bright light across the rough edges of the slide. The doped stuff in the better slides is reddish in bulk transmission. So maybe hard flint or crown glass.

With the exception of Quartz/Fused Silica which has a more defined atomic structure, just about anything should behave very closely when ablated.. Pyrex will of couse take themal abuse better.

Steve

[macona]

If the mirror is really fused silica there might not be much I can do considering that is what my lens is made out of. Possibly if the power density is high enough it might work. I did manage to get ahold of a new beam expander for 355nm so that might get my spot size down some if I install it.

Another option is I could use a diamond bit in my cnc mill and grind out the back of the mirrors in a bath of glycol.

[dsli_jon]

Eric -

I have some fairly-concentrated (52% (!) 'HF'-acid that I was thinking to-suggest you might experiment with.. What I would try would be 'mask' the center-section with a 'stripe' of wax (could use tape for a nice hard-line..), and then try 'painting the edges-thin' with the HF - it's quite good at dissolving / thinning glass.. Scary *, but... with proper-precautions, (..and ventilation!..) it could work, and be fairly 'repeatable' (?)... Plus, I'd love to get *rid* of this stuff.. I don't even like looking at the bottle..

re: '..how to get it to you' (..if you were interested..) would be a very-small amount, 50mL or less, in the proper-plastic container, inside another, and another, etc.. I'd also ship ground / hazardous-materials, etc..

Lemme know, before I get too-upset at how behind I am and drink it.. jk... My renders are done, so I gotta jet.. PM or email me if-interested..
Cost-of-shipping, only...

ciao
j

[planters]

If the mirror is really fused silica there might not be much I can do considering that is what my lens is made out of.

If the focus lens is silica this should not mean the highly concentrated focal spot would not be able to ablate glass. At a high enough intensity the glass will become more absorptive do to non linear effects.

Jon,

This would be fun. But, the principal here, as I set it up, is that if we can reduce the rotating mass of the mirror without significantly reducing the stiffness then we can speed up a given scanner system. Simple thinning of the mirror will not work. If the mirror were to be thinned to 1/2 its original thickness it would become 1/2 as massive, but it would then have1/8 the stiffness. Now it may be that if these mirrors are way stiffer than necessary at the achievable accelerations these motors can deliver then we might get away with SOME thinning. But, the limits will approach each other from each end; the mirror becomes more flexible and the accelerations will increase.

The method needs to reduce the largely dead weight at the neutral axis (mid plane) of the mirror. You can remove a lot of mass here as in more than 1/2 with almost no reduction in stiffness. That is why I discussed the approach to drilling or ablating holes at this plane bored inward some distance from the outside edge. This is the monocoque design that is used in airplane wings. A stressed outer layer spaced by a lightweight lightly loaded spacer acting in compression.

B. Benner has minimized the significance of mirror mass ( and thus the value of lightening) compared to the rotating mass of the rotors. He is correct, sort of. The older generation of scanners (pre diode) can use very small mirrors. But, as the need for more power with diodes inevitably demands larger mirrors, the value of larger apertures will increase. Are you still interested in my 14mm EM's? Even the Scanner Max web site shows the effect of increasing the mirror from 4mm to 8mm by reducing the resonance of the system from 1500Hz to 1000Hz. The effect will be greater for larger mirrors.