Diode laser alignment through all three mirrors

[Travis Reese]

I was toying around with finding a way to get a red diode laser through all three mirrors to help with alignment as well as just generally wanting to see the path of the beam. I've been going back and forth with a guy named Russ in England. He's got some excellent videos about his laser. He pointed me to a video on YouTube by Peter Jensen. He had made what I thought was kind of a neat contraption. It can be found here...

https://www.youtube.com/watch?v=Jm8syz6ARCY

Talking with Russ he thought one of the flaws in the design was that it attached to the frame of the machine and therefore if the tube ever moved it would be out of alignment. In his videos he stresses the tube alignment as well. He suggested it would have been better to attach it to the front tube clamp. I thought even better would be to attach it to the tube. Below is what I started working on. It's just a prototype so forgive the messy wiring. It's also got a few obvious flaws I'm sure you'll see and point out. I'm working on a new design now. But still for a first try I don't think it's bad.

https://youtu.be/yNn_Kunewu8

[Keith Winter]

Interesting idea do you have to remove the tube to make it fit? Maybe you said in the video, cannot hear anything here, but how do you get it at the exact same angle as the tube? It being off even a fraction will throw everything off. Does this provide more information than a beam combiner at mirror 1?

[Travis Reese]

No, you don't have to remove the tube to make it fit. Just slips right over the end and affixes with the four set screws. If you're asking how you get the arm to swing down perfectly in the right spot in front of the tube the answer is that it is controlled by the position of the limit switch. That's why the limit switch mount has slots in it. That way it can be adjusted. By loosening only one screw you can pivot it with pretty fine control. You can also visually look through the tube mount to the "shutter" and align it. This is version 1. I'm going to make a few changes. I could actually put alignment hashes on both the tube mount part and the arm so that I have a visual reference for aligning it. The other issue is that I designed the diode so that it could be steered with the four small stainless set screws you see in the video. The problem I found after I put it together is that only two of the screws are accessible. Instead of four screws I need to use two screws and a spring or spring-like material on the opposite side.

[Travis Reese]

And actually it being off a fraction or even more wouldn't make any difference as long as the tube itself isn't moved toward or away from mirror one. Once the beam is steered so everything is coincident at the end you could move the tube forward, back, up, or down without any difference. You just couldn't move it toward or away from the mirror.

[Rich Harman]

With that plastic piece clamped onto the end of the tube I would be concerned with contaminating the output window.

[Kev Williams]

On my LS900, I found when adjusting my red dot that the spot can hit virtually anywhere on the last mirror, and the focused spot on the table varies at most, maybe .002"... it seems the beam exits the lens straight regardless of the angle, or where the beam enters the lens.

On the other hand, I've found that aiming a hand-held pointer an inch from the last mirror does result in a lot of focused spot movement.

[Travis Reese]

Rich, contaminating the output window how? I don't understand what you mean.

[Keith Winter]

And actually it being off a fraction or even more wouldn't make any difference as long as the tube itself isn't moved toward or away from mirror one. Once the beam is steered so everything is coincident at the end you could move the tube forward, back, up, or down without any difference. You just couldn't move it toward or away from the mirror.

If you move the tube beam up, back, or down in the mount it most definitely will affect your alignment. You've changed the beam path and now you get to align from the beginning again. Same if your alignment tool wasn't perfectly square on the tube, you couldn't get a precise alignment.

You can get sloppy alignment using a beam combiner on mirror one with similar effect I don't think it would be as precise as what you're trying to do though. The hardest part would be getting it 100% square to the tube and in the exact beam path of the tube. Maybe 90% or 95% but very hard to get 100% I would think.

[Travis Reese]

I agree that will definitely affect the alignment. What I meant is that it would affect where the diode hits mirror one relative to where the beam hits mirror one.

I'm already working on version 2 of this.

[Rich Harman]

Rich, contaminating the output window how? I don't understand what you mean.

You will have heat and other radiation on that plastic, being just a few mm from the output window may cause some undesirable things accumulating on it. Of all the optics you have in the laser, that is the one that is the most sensitive.

I don't know if that will happen, but it would concern me enough to not do it.

Also, the plastic will serve as an insulator, holding more heat than it would otherwise.

[Keith Winter]

Interesting idea though, don't let us discourage you, just be careful not to damage your tube playing around with it.

[Rich Harman]

I did not mean to discourage. I even made something similar myself a while ago but it was meant to clamp (press) onto the tube only temporarily.

I very much disagree with Russ that it would be better to mount to the tube. I think it would be much better to mount to the frame. Yes, if the tube moves (it shouldn't) you would need to realign - but you would need to realign all the mirrors too. So the advantage I think is insignificant.

I would also do the electrical differently. I would use a switch to operate it, and use a limit switch in series with the water flow sensor to prevent the laser from firing when it is in the way. That's because I often laser with the lid open.

[Travis Reese]

I appreciate the comments. I'm working on a more compact version 2 at the moment. Will post when I get something to show.

[michael croft]

This may be of interest on this subject + the rest of his tutorials are good as well https://www.youtube.com/watch?v=-w9f8fZujlw

[Travis Reese]

Michael, the video you mentioned is from Russ who I mentioned in my first post. I've watched all of his videos. He and I have been going back and forth on this project I'm working on. They are an excellent resource for anyone getting started.