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Laser Mounting Fun

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LAN_403

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Sun Oct 22 2006, 08:28AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I hope it has been 48hrs...

IT LIVES

I mounted one of my 23 ~20w 808nm bars, and fired it up at 1:03am PDT.

Setting a solar cell in front of it (very rough estimate) gave a running current of ~20 amps, and an IR card showed the threshold to be about 5 amps.

Runs were limited in length becuase it was still mounted on my small hotplate, which isn't the ideal heatsink...

What suprised me the most was that the beam is almost round at about .5" in front of the array (the fast axis happened to have diverged 1cm; the lenght of the bar).

Some shots of the laser

croped version showing the bar well below threshold

Will try to give a little more info later today, need sleep

Steve Conner

Sun Oct 22 2006, 11:56AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

That's pretty impressive! What is the first picture, a piece of foam plastic burnt by the beam?

Marko

Sun Oct 22 2006, 12:12PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I hesitated to reply because I was ashamed of my ignorance :/

IIRC, your ssy1 yag is a heavily-dobed for pulsed operation, how you plan to run it with CW diodes?

How do you solder the dies to tin? Are they metal-plated already..?

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Sun Oct 22 2006, 07:31PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

The first pic is a piece of antistatic foam that was held ~.5" from the array. The holes are 1cm in diameter. I should point out that the beam coming out of the array is not normally round, but rather a 1cm line that is slowly diverging (at a few degrees- called the slow axis) in width, and very highly divergent on the vertical axis (like 90degrees- called the fast axis). It just so happened that at .5" away from the bar the fast axis had diverged 1cm, which was the length of the slow axis, which gave a nice beam. It would not work to put a lens in front of it to get a smaller spot, you would get a line ~1cm long.

Don't be ashamed Firkragg, I was asking that same question 2 weeks ago

Basically, the doping of the yag is not very crucial, just so long as you have enough it will work. For flashamp bars they use a very high doping (like 1-3%) because it has to handle very high pulses. For diode lasers we use lower doping (like .5%) because we are running considerably (well, in most cases) lower peak power. The added Nd ions are harmful, they are not too large of a problem.

The reason that I cannot use a ssy-1 head unmodified has to to with the % reflectance of the output coupler (OC) mirror. No one knows the exact reflectance, but we think is is ~80%. This means that you have to have a lot of power into the bar before you get enough feedback for it to start lasing, which is good for a flashlamp pumped laser. I am going to replace it with a much higher reflectance (~98%) one, which will give a much higher amount of feedback, which will hopefully lower the threshold to a reasonable value. (sam noted that it might even work at a few watts)

As to soldering these guys down, they are already gold plated on both sides. All you do is set the copper mount on a how plate set for ~110c, add some flux (I am using a normal flux pen, but it doesn't seen very soluble in IPA, so I may try something different), add a very small amount of solder (melting point = 97C), and use a q-tip to smear it around. Now set on a bar, shiny side DOWN (put it in upside down the first time >_<) and pray that you got the side the light comes out forward (got that backward the first time too) and if all went well it will suck down onto the solder and life will be good. Use a cut off q-tip (ie the wooden stick side) to position it exactly on the edge of the mount. Then let it cool, add a little more flux on the top of the die, heat is back up and add a tine bit more solder to the top, then smear with a q-tip, and wipe most of it off. Then grab a piece of copper foil, add some flux, set on the plate, tin the tip, wipe the solder off, then carefully set it on the bar (with an insulator below it) and then bolt it down. I had to use a piece of copper to put some pressure on the whole sandwich while it cooled to keep everything nice and tight (you want to have the absolute minimum amount of solder between the die/copper block since indium isn't the greatest conductor, and be positive that there are no bubbles under the bar or the temp will be uneven and the wavelength wont be constant across the whole bar).

Viola, GaAs sandwich

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Tue Nov 07 2006, 01:51AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I just wanted to note that I am still slaving away with these diodes (I not done anything not related to lasers or school besides attend a scout meeting and go trick-or-treating in weeks) and am making some progress. I have mounted 2 more bars, although that has not been my primary focus.

Some of you diehard 4hv fans may remember MdFluffin's thread about some green modules he acquired here. Since he was in the buy of the laser diodes, we decided that I would take a stab at fixing his modules.

So he shipped then over, I took then apart, and determined that all of his diodes were dead (not having an optical spectrometer I just held my combination vandate/ktp crystal in front of the laser running a 1A, and none gave any green).

So I needed 3 808nm laser diodes... Then I looked at the bars and thought a little more. Then I got out the exacto knife and after sacrificing most of a bar to the laser gods I managed to cleave out a few laser chips.

So I soldered one down to the c-mount on his laser, and then bolted the mess back together, and viola it worked! I ran it at 1.2A for ~5 hours and it seemed really dependent on temp (I have seen anywhere from 5mw to 75mw) but placing the whole module on a heatsink (so it stayed at room temp) I got a pretty stable 20mw of green. Just enough to see the beam in artificial light.

I also made up some labels for my diodes based on the info that I got from the ones I mounted, and listed one on eBay here

edit:
Some yag rods just showed up, as soon as someone posts I will post pics. Green laser repair pics available if requested.

McFluffin

Tue Nov 07 2006, 05:47AM

Registered Member #119 Joined: Fri Feb 10 2006, 06:26AM
Location: USA
Posts: 114

Well, being partner in crime...probably about time I say SOMETHING on this thread. Just been a bit busy. Anyway, too bad about the YAG rod, hope everything works out with that. Worst part is I live near the person who shipped it and I believe they said I could have inspected and probably picked it up myself. Then I could have shipped it off safely. I have a large (0 to 7.5V, 0 to 150A) power supply coming to me to test the diodes. Just hoping it is regulated enough. I ordered a largish TEC for the PGL lasers which I'm hoping will help with that. Might get something smaller later, but it would be good to have as a general purpose cooler to mess with. Hope all goes well with eBay.

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Tue Nov 07 2006, 06:37AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

The yag rod John is reffering to is this:

The seller (who will remain nameless until the problem is resolved) packages it as so:

And in shipping it it snapped one of the ends off. That yag may be strong, but it isn't up to UPS without some protection...

In any case, I did get one rod in tact

And some mounts

Unfortunately the mounts are for a 1.6mm rod, and I got a 1.2mm rod, so there is .4mm of play. While that doesn't sound like a lot, it should be like .01mm or something insanley perfect. But then again the mounts were free so I can't really complain

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