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Filling laser optics with nitrogen gas

BlackOps

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I want to fill my laser optics with nitrogen gas. The reason is, my lasers are watertight including the lenses, the entire cavity is sealed, even around the diode. But i have a major problem

As soon as i put it in the car and turn the Anti fog and heater on, it condenses like crazy inside the lenses. Or if i clean it with cold/hot water.

There is no leak, i could leave it in 2m deep water for a week and nothing will enter.

I need to get 0% humid air in there or (more preferable) nitrogen gas. I've done research and unfortunately found no answer. I know military optoelectronics and sights like scopes get filled with nitrogen

Can anybody explain me how i could trap nitrogen gas in there. Yes, the entire optical system is completely airtight. Any help is highly appreciated!
 
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BlackOps

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Btw the country i live in has very humid air, thats the only drawback for me having a sealed unit
 

BlackOps

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You're making this way harder than it needs to be. Google "desiccant".
Hi thanks for your reply. The desiccant wouldn't work if you mean to put it inside the lenses. The space inside the optics is less then a mm. Maybe i misunderstood something
 

steve001

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This is technically far beyond what you can accomplish at home. Even if you could, you would need dry nitrogen gas, meaning nitrogen without moisture in it.
 

BlackOps

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This is technically far beyond what you can accomplish at home. Even if you could, you would need dry nitrogen gas, meaning nitrogen without moisture in it.
Hi, thanks for your answer. Nitrogen gas is dry, it is non hygroscopic. It couldn't absorb moisture.

Do you know a way to get dry air at home? I did some research about desiccant, my idea would be to leave the laser in a ziplock bag with desiccant packages and the lens open for a day or a week and assemble it inside the bag ( without opening it). Do you think that would create completely dry air?

Edit: nitrogen does absorb moisture, sorry for the mistake of sharing wrong information
 
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Gadget

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That's probably gonna be your best bet to dry the air inside the optics cavity. You'd definitely need to reassemble it without opening the bag, too.

-G
 

BlackOps

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That's probably gonna be your best bet to dry the air inside the optics cavity. You'd definitely need to reassemble it without opening the bag, too.

-G
Hi, thanks for your response! I can easily assemble it while in the bag. The laser is small. I have taken it apart and made clear there is no dust inside the bag, and have put it in there among with a silica gel package. How long do you think i have to leave it in there? Also, i removed most of the air.

Thanks
 

BlackOps

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Did you use a vacuum pump to evacuate your cavity?
Hi thanks for your answer. I did not use vacuum to remove air. Vacuuming would put to much stress around the diode seal and vacuuming the bag would make it too hard to put it back together while inside the bag. I removed as much air as possible tough by flatening the bag while still be able to maintain clean optics and being able to put it back together.

Thanks!
 

diachi

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BlackOps - please avoid double posting - use the multiquote button to respond to multiple people at once.

Thanks!
 

BlackOps

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BlackOps - please avoid double posting - use the multiquote button to respond to multiple people at once.

Thanks!
Hi, i will do that next time never tought about that button sorry
 

steve001

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Hi, thanks for your answer. Nitrogen gas is dry, it is non hygroscopic. It couldn't absorb moisture.

Do you know a way to get dry air at home? I did some research about desiccant, my idea would be to leave the laser in a ziplock bag with desiccant packages and the lens open for a day or a week and assemble it inside the bag ( without opening it). Do you think that would create completely dry air?
You wrote: "the optical system is completely airtight". The answer remains "no". The answer to all other questions in this specific post can be answered with a "no".
For the fun of it. Assuming for a moment this optical system is not absolutely airtight what I would do is place it in a vacuum chamber, create a vacuum in the chamber and optical system. Then shut off the vacuum pump valve while maintaining a vacuum. Then I'd break the vacuum by injecting dry nitrogen gas into the chamber until the pressure is equalised with ambient atomospheric pressure. But that leaves one problem. Since it is possible to suck out all the gas in the optical system that means it leaks; overtime moisture will work it's way back in.
 

diachi

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Desiccant is the way to do it, may not be practical in a pointer. That's how they do it in lab lasers. I've seen it done with "external tanks" filled with desiccant on some lab lasers, where they'll have a metal tube with an O-ring that seals around the Brewster stem. The desiccant tank as attached via a hose to a hole on the metal tube.

Not very practical in a pointer unless you design it that way from the start.
 

BlackOps

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You wrote: "the optical system is completely airtight". The answer remains "no". The answer to all other questions in this specific post can be answered with a "no".
For the fun of it. Assuming for a moment this optical system is not absolutely airtight what I would do is place it in a vacuum chamber, create a vacuum in the chamber and optical system. Then shut off the vacuum pump valve while maintaining a vacuum. Then I'd break the vacuum by injecting dry nitrogen gas into the chamber until the pressure is equalised with ambient atomospheric pressure. But that leaves one problem. Since it is possible to suck out all the gas in the optical system that means it leaks; overtime moisture will work it's way back in.
Hi, i didn't know all that was required to fill it with nitrogen gas. I tought getting the gas, getting a ziplock back and fill it up and screw the lens on there and trapping nitrogen in there while the bag was closed. Air couldn't escape from the cavity. The sealing is hard and the 3 element lens is sealed with strong thin adhesive cut precisely at the diameter of the lens and rim. which is pressed in place with the retainer ring. The diode is epoxied where the 3 cutouts are on the diode substrate and sealed around the module and the diode can with sealing gel i got from an electrician/boiler mechanic. I sealed everything my self. Threads are sealed to with a ton of teflon and the gel at the end when its focused to infinity. There is no way air could escape. Maybe after 6 years but absolutely not now

It could easily handle presure diferential, it could handle vacuum too for a long time. Altough i don't want it be vacuum as it puts more unnecessary strain. I tough you meant facuuming it and then seal it

Desiccant is the way to do it, may not be practical in a pointer. That's how they do it in lab lasers. I've seen it done with "external tanks" filled with desiccant on some lab lasers, where they'll have a metal tube with an O-ring that seals around the Brewster stem. The desiccant tank as attached via a hose to a hole on the metal tube.

Not very practical in a pointer unless you design it that way from the start.
Hi, i tried a ziplock bag and a desiccant bag. By drying the air inside and then sealing it off while dry air is inside. Altough, do you know how long it takes to dry air inside a nearly flattened ziplock back? I think this is by far the best way to get dry air inside my 100mm long pointer.

I also want to use this as laser sight for airsoft soon, i can't have it to condensate. The humidity here is terrible


Anyways both thanks for the inputs!
 
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