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Thread: MgF2 coating

  1. #1
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    Default MgF2 coating

    I am putting things together to do some evaporative coating. What purity of MgF2 is normally used for AR coats? I am having a hard time finding that info.

    My system here:

    http://projects.hackaday.com/project...for-Deposition

    I plan on adding a small 3 pocket ebeam setup and maybe a couple small sputter heads. Hoping to do dielectric filters and other optics.

  2. #2
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    99.9999% (four nines) or better for commercial use. Deposition slugs are usually the highest purity materials obtainable. If the E-Beam hits a pocket of something that should not be there, one of the results is the material gaining excess kinetic energy and leaving its pocket, making a mess. Get a on line subscription to VS&T and look at the ads. Ie Kurt Lesker and other companies. VS&T = Vacuum Science and Technology. They guard who gets free subscriptions, so you will have to apply using a valid company.

    For hobby use, 99.99 is good, but it often needs to be crystalline and melted together to make a slug, in vacuum.

    Old, 1960s "soft" coating materials (and a few "hard" coatings) can be evaporated from tungsten or moly vacuum boats, heated by AC passing through them. I'd start there with two boats, two simple shutters, and a optical or preferably crystal thickness monitor. See Lesker or www.Tungsten.com for the boats. Midwest Tungsten is nice for small purchases. Soft means the coating is easy to make, but can be water soluble.

    Congrats on finding a more expensive hobby then lasers, Vacuum is all most up there with "full size airplane" in price.

    0.5x10-7 Torr minimum vacuum for Ebeam, nothing less. A chamber that size usually gets a Cryo baffle pump for Ebeam. This needed 2-4 gallons of LN2 on the one I worked on.

    Aluminum is easy, you just need one (or more in series) of Midwest's conical spiral cathodes, and a low voltage transformer. One thing to know, a tungsten spiral that needs 100-200 watts to get to glowing red in Air, needs next to nothing to heat it in vacuum, if its mounted correctly. I popped small cathodes often, from surges. Thus I learned to use a stepdown transformer, on a Variac, not just a Variac. Thin aluminum wire, not AL foil. DO not waste time with AL foil from the kitchen. MIG welding wire, tiny size, is worked OK.

    See Dr Csele's page:

    http://technology.niagarac.on.ca/cou...icMirrors.html

    He uses MgF and ZnS with his students, which you should try, as they are "easier"

    Be careful with the Ebeam power suppy, 4KV at 2-4 amps is not chickenfeed.

    Lack of thickness monitor is a witch. For a single wavelength, You can do hene mirrors for example, using a photodetector, a chart recorder, and a HENE as the source. Every quarter wave of dielectric material you'd see a peak or valley on the recorder, but..... Not easy, and needs one or two AR coated windows on the chamber for the beams.

    C.L. Stong's book covers home made evaporative coatings fairly well.

    Really good chambers have a heated target area and a planetary to spin the optics (if more then one) for uniformity.

    See if you have a local vacuum metalizing shop, and ask for a tour. However their systems are usually quite crude, huge chamber, big Diff pumps, array of simple heaters.

    Steve (who's only done one layer E-Beam, evaporative boat, and sputtering of palladium, long ago.)
    Last edited by mixedgas; 03-22-2014 at 05:43.
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    Hey Macona;

    Please do let us know when you get this working.

    As a laserista specializing in lumia, I have a bunch of glass that needs AR coating for 520-532nm, 445-478nm, and 635-660nm.
    BBAR would be nice as well.

    I would be delighted to send you samples for testing.

    I spent some time a year or so ago trying to find a US co. that would do this in small quantities, no luck then.

    Thanks…Mike
    Runs with Lasers

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    Click, Be happy if you can get a single layer "V" type AR. BBAR needs 5 or more layers.

    Steve
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    Ah, I didn't know that; thanks for the info.

    I would be quite happy with single layer; I have a large number of lumia disks and torture tubes that would benefit from this.

    Is there a restriction on the type of glass this can be applied to? Most of my stuff is commercial textured glass, purchased from a stained glass supplier.

    Thanks…Mike
    Runs with Lasers

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    Mike,

    three things:

    You need to heat the glass while applying the coating so that the coating will adhere. No where near melting, but quite hot.
    For best results, you need to know the index of refraction before applying the coating. This is easy for lead/lime glass.
    You'll reduce your back reflection only 4-5%. The rough surface will still contribute some back reflection.

    Steve
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  7. #7
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    I have a couple thickness controllers already, an Inficon XTC and the one I will probably use, a Sycon STC-201. I also have an old maxtek and an old crc if all else fails. The sycon is a bit more configurable than the inficon. I installed a new bakeable inficon crystal holder too.

    The system already has a three station evaporator in place, two for filaments and one for boats and I have a bunch of new moly and tungsten boats too. The setup has a transformer good for about 6kw. This system came out of Portland State from a professor I know.

    As it is now I can get down into the -7 range with a good bake out. I also have an RGA on the system too. I have a Large 2000 l/s turbo I am hoping to get working to replace the diff pump with. I found the controller for it, I need to sell the other stuff I have and cant use to buy it. If all else fails a friend has a couple cryo compressors and I can scrounge up a cryo pump.

    This is the e-beam gun we are going to build. Just a little 3kw unit which is all I really need. Runs at about 4kv and 750ma. http://www.thermionics.com/en-us/Des...-56f2c60604b6/

    My big turbo, Seiko Seiki mag lev, 2000l/s, ISO-250 (10") flange.



    The RGA on the system, Dycor Dymaxion 100AMU. Real nice for finding leaks and contamination.


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    Oh, and I got the ring for the planetaries last weekend and I got the aluminum to machine the mount for the ferrofludic feed though to drive it. I see one 18" holder on ebay now which I am going to grab.

    For sputtering I am going to build a couple 2" guns, I have a Advanced Energy 2.5kw 450khz RF generator to drive them.

    This machine came out of Tektronix way back.

    I have a few books on thin films, Vacuum Deposition of Thin Films by Hammond, Thin-film Optical Filters by Macleod, and Handbook of Thin Film Deposition by Seshan.

    Thanks for the info on the MgF2. Nothing has really touched on purity requirements.

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    Quote Originally Posted by clickamouse View Post
    Ah, I didn't know that; thanks for the info.

    I would be quite happy with single layer; I have a large number of lumia disks and torture tubes that would benefit from this.

    Is there a restriction on the type of glass this can be applied to? Most of my stuff is commercial textured glass, purchased from a stained glass supplier.

    Thanks…Mike
    Not really a big deal, there are a quite a few companies that do dichroic coatings on art glass for blowing and stained glass type work.

  10. #10
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    This was fun, best I could do with a 12 layer coating for reflect 1121 kill 1064 (yellow ND:yag) was 85% at 1121, 9% at 1064. 12 layer coating cad:

    http://www.lightmachinery.com/Thin-film-CAD841.htm

    After playing with the optimizer,
    It seems if you want fewer layers in your coating, you really need a BIG difference in your indexes, ie the high temperature stuff that needs E=beam or Ion to put down.

    Steve
    Last edited by mixedgas; 03-26-2014 at 13:56.
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