Laser alignment heck

Ok, so for the last several weeks I’ve had a functionally dead Spectra Physics 907 laser.

I managed to tweak it past the point of lasing and had to start the arduous process of learning to align this kind of laser from square one. I then spent the better part of two weeks trying to align the laser myself but could never get the beam quality back the way it was before I screwed it up.

What follows is what I’ve done so far to get my laser fully alive again. It’s still not working but hopefully soon it will be.

I took it to a local expert last week and after cleaning and six hours of tweaking I had a better appreciation for just how difficult this process can be (in other words I felt a lot better about how hard a time I was having) and better understood the methods to use for alignment. At the end of that night I had a laser that was doing 30mW according to his meter but only 13mW according to mine.

Given the time I decided that was good enough and took it home with the intention of tightening the alignment nuts so they wouldn’t go out of alignment easily and tweaking the power back up to maximum.

Unfortunately there was a tear in the OC boot that I think let in dust and there was a lot of light coming off the front brewster window.

Realizing that I’d need to start at square one again I set about building a rig to make the job easier.

Shown is a setup that allows me to get the laser high enough that I can get to the bore alignment screws and allows me to clamp the laser down to a stable surface and hold all but one of the elements needed for me to align the laser.

That one element is a mirror past the HR that can be used to reflect the light from the alignment laser closer to the “operator.” That’s important because when shooting the alignment laser down the bore you really need to be able to get a close-up view of the beam coming out, which is difficult when you’re at the other end of the laser. Fortunately I have an extra tripod which now holds a small mirror, just for this purpose.

Toward the front of the rig I’ve got my alignment laser, a 5mW green pointer, aimed at the first mirror, reflected to the second mirror and then through the bore.

Here’s a view of the OC end with the mirror off.

And another with the torn boot off and the bore Lit.

First task is to find out where the bore light is shining on the second mirror, so that the alignment laser may be aimed as close to center as possible. Here I’m using some photo tissue to do that job.

Next aim the alignment laser and tweak the first mirror screws to put the beam at the center of the bore light.

The next task is to tweak the second mirror to shoot the alignment beam through the bore…

And continue tweaking until you get just a spot of light out the other end. Depending on your alignment laser you may never reach this latter goal but you should end up with at least a clear dot in the center of any swirls.

So… Is my laser aligned and running at 25mW again?

No. Unfortunately I ran out of time this morning but will continue the task this evening.

On the other hand, I was able to gently wash the boots and repair the tear in the OC boot as well as clean the brewster windows so there’s no dust or scattering of the alignment light. That should help a lot with the final beam quality.

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Michael Harrison

Husband, Programmer, Irish dancer, tinkerer, astronomer, layabout (as much as possible)

2 thoughts on “Laser alignment heck”

  1. Being the continuing saga of Laser Alignment Heck
    So, the laser’s working again and power levels are somewhat close to what they were before this adventure began.
    I don’t have many pictures of the process I went through last night. Andres came over and

  2. After several weeks of fiddling with my laser, it’s now fully working and back on the table.Many thanks to all those at the Holography Forum who provided suggestions for getting the beast aligned.Also many thanks to Sam Goldwasser for making public all

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