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"Joules" the 60J ND:Glass laser

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Daedronus

Mon Nov 23 2009, 10:06PM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
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Posts: 370

Interesting, I have a almost identical head in the mail bound for me.
But mine has a slab 3x9x360mm

Discharge length...sorry I didn't word that quite right. I meant the length of time it takes the capacitor to dump it's energy in the flash lamp.
The discharge time for example for my yag is about 30-40ms.

Longer discharges usually mean less violent results, the laser will tend to burn things instead of exploding them.
If you want all the laser energy in one single pulse the capacitor must dump it's energy in less then about 200us.

Usually for cutting/drilling shorter pulses are used and for welding longer.

Z28Fistergod

Tue Nov 24 2009, 01:19AM

Registered Member #2040 Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180

Daedronus wrote ...

...
Discharge length...sorry I didn't word that quite right. I meant the length of time it takes the capacitor to dump it's energy in the flash lamp.
The discharge time for example for my yag is about 30-40ms.
...

Oh ok, I should have been able to figure that out, 350us.

Z28Fistergod

Wed Nov 25 2009, 07:32PM

Registered Member #2040 Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180

I've come up with a method that I think will help me align the laser better. I'm going to adjust the mirrors individually to get the lowest lasing threshhold, then I will "walk the beam" to get the lowest lasing threshold. The lasing threshold should be a much more accurate indicator of alignment than the sound or look of the explosion.

Daedronus

Thu Nov 26 2009, 09:36AM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
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Posts: 370

Post a picture with the burn marks on the black plastic thingy.

For a lens, i have a few of this:

If you don't care for the AR coatings you can probably get something cheaper.

Z28Fistergod

Thu Nov 26 2009, 11:36PM

Registered Member #2040 Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180

I abandoned the minimum threshold method and went with your suggestion Daedronus. Although I don't have a beam-expander, the beam is fairly wide as is and I've got it pretty close. I will post a picture when I can. I noticed that at full power the beam is quite a bit wider than the actual rod diameter. Maybe 1.5 - 2 times as large at a distance of 1 foot. I meant to check it at varying distances from the laser head, but I ran out of time this morning. I heard it mentioned that this can be caused by dirty or scratched optics.

Fri Nov 27 2009, 04:51AM

Registered Member #2372 Joined:
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What is the focal length of the high reflector compared to the cavity length, if that number is way off the laser wont work very well. Also if you put a pockels cell or AOM into the cavity and cavity dump the laser you can get the pulse length down to a few 10s of ns and kick up the power by several orders of magnitude.

Daedronus

Fri Nov 27 2009, 09:00AM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
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Considering the whole assembly is factory made, I would expect the mirrors to be matched to the cavity length.
But, yes, the divergence depends solely on the mirrors and cavity length. Dirt or scratches are not going to affect that.

Z28Fistergod

Sat Nov 28 2009, 01:21AM

Registered Member #2040 Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180

I spent a few hours adjusting the mirrors. The beam isn't perfect, but it's getting close. The picture shows that the burn marks are quite a bit larger than the rod diameter. I measured the rod to be 6.4mm, so the burn marks are almost twice as wide.

The HR should be matched to the resonator, but who knows what they did to it before I got it, or if it is curved at all

I checked the beam at 1 foot and 4 feet from the laser, and there was no noticable divergence.

I mentioned before that the shutter has a massive scorch mark on it. The face of the shutter is positioned about 3.5 inches from the OC. I wonder if molten aluminum from the shutter splashed on the OC and forced whoever to replace it, possibly with a mirror that didn't have the proper reflectance.

Daedronus

Sat Nov 28 2009, 03:46AM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
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Posts: 370

To get a general idea how the geometry of the resonator influences the beam I recommend playing a bit with this simulator:

and, yes, it's free :)

Are there any other optics in there? it's hard to believe the rod is 6mm and the burn marks 12mm. Can you double check the rod diameter or if there are any other optics?
The burn marks look OK now, where they this uniform from the beginning?

Z28Fistergod

Sat Nov 28 2009, 04:46AM

Registered Member #2040 Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180

Daedronus wrote ...

Are there any other optics in there? it's hard to believe the rod is 6mm and the burn marks 12mm. Can you double check the rod diameter or if there are any other optics?
The burn marks look OK now, where they this uniform from the beginning?

The burn pattern wasn't too bad to begin with.
All measurements were made with calipers.
There are no other optics, just one HR mirror, one OC and one rod.

The rod is surrounded by opaque plastic, so there is no way for any light to pass from one end of the resonator to the other unless it's inside the laser rod. Whatever is distorting the beam is between the front face of the rod and the target. The only thing between the two is the OC, so I think it has to be the culprit.

Here is an identical spare rod for reference

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