Using Fiber Optic Cable

[andrewblanejr]

Would it be feasible to use fiber optic cable to carry the co2 laser beam to the head assembly, rather than mirrors? I assume there is some reason why this isn't already being done. Anybody have any idea about this?

[r691175002]

Glass that won't absorb mid IR is very expensive. Getting the 5mm diameter beam into a fibre to begin with will cost many times more than a set of mirrors. My guess is around five figures.

[andrewblanejr]

damn...

[mattrsch]

We just demoed one of these laser tool cleaners at work the other day: http://adapt-laser.com/lasersystems/mobile/CL500Q.html
It passes the beam from a 500W YAG laser through a single fiber to a handheld scanning tool.

One thing you have to watch out for on fiber optics is if your bend radius gets too small the light will escape the fiber.

I looked into an IR through fiber application for work a couple years ago. I'll just say that I don't doubt r691175002's guess.

[dirktheeng]

We do this in the lab all the time even with powerful lasers. There are 2 types of wave guides you can use, a fiber optic and a holow wave guide. A fiber optic is solid glass and very expensive. You can get them for around $1000 to $1500 for 1000nm. As the previous post says you have to watch out how much you bend them, not only will they leak, but you can break them easily too and that really ruins your day.

The second, cheaper alternative is the holow silica wave guide. Basically, this is a capilary tube that is coated on the inside with reflective silver or other metals. You can actually make them yourself and we do in the lab. We use them to make experimental raman spectroscopes. Basically, you focus the laser into the center of the entrance (you could even do that with the lenses we have now). The light will reflect to the other end. It will not come out at a divergant angle rougly equal to the focal angle and can be columated and refocused. You can buy these for between $300 and $800. The thing you have to watch out for here is not bending it much. It can break but also bending it messes up the intensity pattern. That is, if you put in a spacial distribution of laser light that is gousian accross the diameter of the beam, it will not come out that way. It can be multi-modal depending on the ratio of bend radius to wavelength. It can mess with your divergent angles as well, but that isn't the main problem. I think you may end up with laser focal shapes that are no longer round and could be varriable depending on where the laser head is.

The other thing that neither of these type of guides can handle is a dirty environment because any contamination that would cause IR absorption will end up melting the glass especially with high power lasers. Anyhow, you would need a minimum of 3 IR lenses and a minimum of $500 or so to get the guide so you are already 10x the cost of the mirrors. I thought about doing this as well, but it is not as easy as it sounds at first. There is a reason why most of these systems do not use wave guides.

[andrewblanejr]

Thanks for all the information guys. I figured there was a reasonable explanation for why we don't use these. The fiber optic cables that are used for networking equipment and audio (toslink) are actually quite cheap, <$10/meter...if only they could be utilized. I had originally thought of this because of so many forum comments about how difficult it is to align mirrors on larger lasers. Also I have noticed that it seems like there is a just a little bit of mysticism/uncertainly/difficulty about proper focus and beam cutting angle. If only they made these laser tubes with fiber optic ports built in