DPSS Laser Gloat!

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DPSS Laser Gloat!

Postby Jerry » Sun Jun 24, 2012 5:51 pm

Got myself a new toy. A friend got a lot of Diode pumped solid state lasers that had issues from a local company that is moving production off shore.

Well, I got one of them, one was different than the others, q-switched 532nm (green) output instead of the 335nm (uv) that most of them are. Found a couple problems. One was the coax connector for the q-switch in the AMP connector was pushed back in where it would not make contact. Second one of the CPC water connectors on the head was broken internally and ways probably not letting full flow, if any. So I fixed these two issues. I also got a couple thermoelectric chillers, both were prototypes from china for a local laser company that used these heads. I found the pinouts for the chiller connector on the power supply on laserfaq.org.

Darn thing works. Has 1489 hours on the head. According to the built in power meter I am getting a pretty stable 6.5 watts at 10khz. An external power meter head is telling me over 7 watts. Don't know what to believe, I will stick with the lower of the two. I am thinking the two problems I found might have been why the head was taken out of service. Seems to be outputting what it was designed for from the label.

Yes, I do have laser googles. OD11 & 514nm.

Couple of pics. Firing it onto a piece of EDM graphite.

Image
IMG_2282 by macona, on Flickr

Image
IMG_2283 by macona, on Flickr
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Re: DPSS Laser Gloat!

Postby Starfire » Sun Jun 24, 2012 7:03 pm

Way to go Jerry but be careful at that power it will burn - can you modulate it? - does it have a pockle cell?
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Re: DPSS Laser Gloat!

Postby Jerry » Mon Jun 25, 2012 3:58 am

Oh yes, it burns very well. Took a lens and was cutting though stuff pretty well. I am not sure what kind of Q-switch it uses. All I know is it is RF driven.

It's not really modulate-able. You can trigger the firing though with an rf signal. You can add an external AOM to get modulation.

I got the chillers tied into the control and it really stabilized the output. The control has a internal PID loop and that controls the temp for the laser diode. Now after warm up it stays at a constant 6.6 watts at 12khz. That is a lot of green.

I shot it out the back door this afternoon to get an idea of the beam size at a distance. At about 40 feet it is about 1" in diameter.
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Re: DPSS Laser Gloat!

Postby Jerry » Mon Jun 25, 2012 4:24 am

These chinese chillers are a joke. I have already had to do some redesigning. I can see why they never went into production. The PC boards are not bad, everything else, well...

The water reservoir on one is just a drinking bottle at an angle with fitting glued in place. Hoses are electrical taped together. Had a problem with the smaller of the two, one of the power supplies kept overloading. It has two 24v, 15amp power supplies in parallel. Well, it seems these power supplies do not like to be paralleled. One takes the whole load instead of sharing. Even putting diodes in between did not get them to behave. The power from the supplies is fed to a board with 6 relays and a driver IC. The power is all on a common bus. So I took a knife and cut the traces on the positive side and ran half the TECs on one power supply and half on the other. Much better. The power supplies are much happier. They were making funny noises when they were tied in parallel too.

One problem was the larger of the two chillers does not have enough capacity for the laser head. The diode temp creeps up past the specced temp and the laser looses efficiency with the wavelength out of whack. So I decided to tie the two in series. I replumbed the small chiller to bypass the pump and the reservoir and put this in series with the big chiller. The next problem is that the small chiller only goes down to 18 degrees c. The diode needs to be at 17.3, so that aint going to work. The temp is read with a NTC thermistor on the line. So I stuck a 30k resistor in parallel with the thermistor which offset the temp by about 10 degrees. The temp is not critical. I could have bypassed the control altogether but I wanted to keep the I/O connector on the back useful. The power supply for the laser has an output line that would control the refrigerant valve in the chiller. I used this to control a small signal relay to close the chiller on/off inputs. The power supply then controls the diode temp with the chillers with it's own PID loop.
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Gloat Part II

Postby Jerry » Wed Jun 27, 2012 7:16 am

Got another head and power supply. This is the 355nm (UV) version. I can get about 4 watts out of this one. Thats not terrible for a laser that has 20000 hours UV time.

Here it is with the beam passing through a quartz cylinder with water and rhodamine 6g dye.

-Jerry

Image
Lightwave M210UV-1-HD-V06 by macona, on Flickr
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Re: DPSS Laser Gloat!

Postby Doug Coulter » Thu Jun 28, 2012 5:03 pm

Yum! You should be able to expose PCB photoresist fast with that and a way to scan the beam...that's getting into real interesting wavelength and power turf. And yes, of course, pump dye lasers...
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Re: DPSS Laser Gloat!

Postby Jerry » Sat Jun 30, 2012 5:03 am

The frequency on laser diodes drift as they age. Temperature will also effect their wavelength. I noticed as the 355nm laser was on that the output would raise and then drop so i put the power supply in service mode and adjusted the set point for max absorption. Nos i get about 4.24 watts out according to the front panel. I tried a couple power meters on it and it looks like the internal power meter is way off. They all say it is putting out over 6 watts. The green is putting out about 7.25.

Thought about dye pumping but that sounds like a potential mess. Only way i would try it is if i found a head complete and cheap. And no interest in having anything to do with making pcbs. Not with the dorkbotpdx http://hackaday.com/2012/06/28/an-inter ... rkbot-pdx/
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Re: DPSS Laser Gloat!

Postby Doug Coulter » Sat Jun 30, 2012 5:13 pm

There are a ton of things you can do with photoresist that might interest you. I've been working on a homebrew mix that uses PVA and dichromate which is kind of numb to all but around 335 nm. Think about selective etching or electroplating or chemical machining...maybe even on curved surfaces you can't just contact print. At any rate, that's the bulb that lit up in my head when I heard you had that.
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Re: DPSS Laser Gloat!

Postby Jerry » Mon Jul 02, 2012 5:33 am

That might be worth trying. First I have to figure out beam delivery. Normal optics are not working so hot. Well.. I guess they are. Lenses get rather warm quickly. Normal BK7 optical glass starts dropping right where this laser outputs. The beam actually causes the glass to fluoresce along the path it takes through it. So it is absorbing quite a bit. Also normal mirrors don't work as well. I can cut aluminum foil with the laser and I can vaporize the chrome off a quartz IC mask. So I need fused silica lenses with ar coats for 355 and dielectric mirrors for the same.

I did find something interesting. Insects sure can see the light. Two moths decided to investigate. All I saw was a white flash when they hit! Didn't vaporize them but it did kill them.

I did some adjustments on the temps of the SHG and THG crystals and got the output up to about 6.6 watts. I also got a real laser power meter and the green is actually putting out a bit over 7.
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Re: DPSS Laser Gloat!

Postby Doug Coulter » Mon Jul 02, 2012 9:30 am

I would think any first-surface mirror would do for 335, would it not? Lenses, yeah, not so simple. You could evap Al onto a concave lens and use it as a mirror to focus perhaps? FWIW, once I found a couple key techniques, evap-ing aluminum is a piece of cake and the results pretty impressive.

I've seen some odd uses for photolith that got me going. That's how RCA used to deposit the phosphor dots for color pic tubes in just the right place - you mix the phosphor into the resist, make it hard here and there with the light, then bake the mess and remove the PVA that way, leaving the stuff right where you want it. Ditto china paint to be fired - which is often your classic curved surface, hard to image on otherwise.

Oh yeah, the dichromate/PVA resist is proportional for depositing "gray scale" if you like...
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