The Big Green Thread (I'm gonna regret posting this in the morning)

[steve-o]

Thanks,

The limit to date has been the long wait for the second driver from Badpip, which finally did arrive. The last time I ran the output I was getting approx 1.5W @ 50% from one pump. The beam was TEM00 and a little under 2mm @ the focusing lens and 5mm in dia @ 9M.

That calculates to be 0.333mrad divergence ??? Unbelievable !!! Are you going to post pics of this monster big dawg ?

[planters]

Look at post #335 for some pictures. The performance is actually deceptively better than this because at these low divergences, if the diameter @ the aperture is increased to just under 3mm the beam is still practical for a scanner and is actually SMALLER @ 9M than at the focusing lens and is crazy HOT. The divergence is really a convergence. This is why I always try to give the raw numbers because the finite distances used to calculate the divergence means that by choosing a favorable aperture diameter you can honestly report whatever divergence you like including zero, but this is misleading. I have owned three of the major CN lasers; DHOM, Vashio and Laserwave and there is no comparison, not close.

[steve-o]

Man, I missed a few pages of this thread.. wtf .. Nice looking beam Sir Planters !!

[mixedgas]

Let us proclaim the mystery of the A vs C Axis Quantum defect rates....
Oh wait, this attached page nails it! Hard to get little piece of data.
808 pumping vs tricky but useful 878 pumping is described in the attached quoted page
Quoted for educational purposes from Laser Focus World. Article by nLight, Inc. Staff.

It translates to "You really need to be lucky or blessed to try surplus 878 nm pump diodes from Ebay"

Steve

[planters]

Steve,
Thanks for the article, but I have some serious problems with it.

After reviewing half a dozen articles describing the fundamental (1064nm) output of 808nm pumped vanadate lasers, the typical conversion efficiency is between 42% and 59%. An "improvement greater than 60%" is almost impossible to believe. Furthermore, remember this article?

https://spie.org/x15068.xml?highlight=x2404

I don't personally have access to the 880nm wavelength in order to test this, but the absorption dips shown by the nLight paper appear to be equal @ 808 and approx 880nm when the SPIE article shows that the 880nm absorption is significantly weaker.

What is the advantage of carefully balancing the polarization absorption other to compensate for the squandering of the polarized pump output in non polarization maintaining fibers?

There is a significant advantage in pumping with a wavelength closer to the lasing wavelength to minimize the wasted energy of this essentially down conversion process (this is what is meant by the quantum defect). But, this seems to me to be a separate issue from the polarization issue. nLight manufacturers diode laser pumps. Do they provide a polarization maintaining module as a pump product?

[planters]

Well I am going to share the bad as well as the good. The big vanadate project has been moving along with the occasional delay for a needed part such as the long awaited Badpip driver. The results have been promising, but I am hitting a wall. My second pump diode/ driver setup has been operating for something like 10 hours and I now have two 808nm diodes that have gone LED. I have checked the other diode beam path and there is no way the light from this pump had entered the train of the other.

The scenario went something like this; after the installation, the driver was slowly brought to threshold and this was similar to the current required for the other pump as well as for this system which had to have a diode replaced previously. I originally suspected the first diode to have fallen prey to a stray beam from the first pump. This may still be true, but I am now beginning to have my doubts. Everything was going well and with the two pumps running I continued to manually increase the modulation voltage and the single mode output was around 2.5W @ 50% pump on both sides. By the way, dual end pumping has a little quirk that if the two pump spots are not aligned at each end the mode supported by one will actually parasite-ize the other and the output can drop to less than the output form a single pump operating at the same current. Anyway, on returning to the set up and switching everything on I noticed a lower output and a little misalignment which tweaking the alignment did not fix. So, as usual I I isolated each pump and adjusted the optics for each and I noticed the threshold for the problem pump was about twice what it had been hours before although the 532 beam looked otherwise unchanged. Upon returning a second time the problem diode was now LED from the outset and would not drive the laser. I placed a scope across this diode/pump and switched it on and off and on and off as well as ramping the system up to the previous day's current. No spikes were seen or unexpected tracing.
I then replaced the diode, confirmed the current output from the driver across a dummy load and... IT HAPPENED AGAIN.

As Steve suggested, I am going to send both diodes back to the manufacturer for inspection ( along with the one I previously attributed to a stray beam).

All these diodes have been meticulously grounded. I wear a wrist strap when handling them, operate on an ESD mat, short them when moving them, and avoid any dust generation around the time of handling them. They have Lasorbs installed across them. I am not sloppy, but maybe I have missed something. These diodes are not cheap and this kind of MTTF is a no go. I can't nail this, but with the recent complaints about Badpip's drivers and my own "dead channel" experience with the first one which took so long to replace, I am going to have to resolve this. I will see if the manufacturer has any insights and I hope I am not being unfair, but I am not going to proceed until an alternative driver is available.

This is a shame as this laser was just about to go into a projector and multicolor raman lasers were to follow. If it turns out to be diode damage from the free space optics then I may have to succumb and redo the pumping to a fiber set up. This will be more expensive and bulkier, but may provide another line of defense by making the retro-reflection route more complex and less probable. This lack of a suitable driver for this as well for other projects is becoming intolerable.

[kecked]

As soon as Bill finishes his testing and gives me suitable part values for the new driver I'll offer you up some hand built while they get made commercially. You cover pcb and parts costs and I'll do the rest. Get on adam to get on bill. I've done all that I can do and am just waiting. I can have the pcb done with heavy copper for you so it can hold high current (8-10a). with 1 oz 4a with 2 oz 6a and with 3oz 10a The limit on this design is traces/heatsinks and nothing more.

I tested a badpip driver with a good differently measurement on the sense and there are no spikes seen up past 100khz. slight rounding at around 500khz but I bet that was my osc and maybe his opamp selection. Driver seems solid. I didn't try running them tandem though.

PS: your experience is strikingly similar to how I lost all three of my diodes in my all solid state rgb build. I wonder if we have to short the driver with power off between the dummy load and the diode switch outs. It might be worth putting a sampling scope across the sense and looking at what is happening.

[swamidog]

shorting the driver leads after a disconnect is always a good habit to have... no matter what the driver.

PS: your experience is strikingly similar to how I lost all three of my diodes in my all solid state rgb build. I wonder if we have to short the driver with power off between the dummy load and the diode switch outs. It might be worth putting a sampling scope across the sense and looking at what is happening.

[planters]

Kecked,

Thanks, I will defiantly take you up on that and I would go with the 3 oz. for the full 10A. Even if the diodes suffered from optical damage the current drivers make me very nervous as they were modified by Badpip to allow operation beyond the spec 2A limit/ channel. Heat should be easily dealt with as any drivers I use will be mounted like the current ones on a water cooled heat sink.

[kecked]

these will do the higher current on a PER CHANNEL basis. no need to gang them. I wish I was allowed to share the design. IT is soooo simple that it should work well. As Einstein said it has to be right if the solution found is eloquent. This is such a design.

BTW. if people want bean suppression they can do it themselves on the input of any driver they want. They just need to build a gate like used in audio for noise. Once you hit a threshold bang there is a signal. Since diodes change in the multi MHz range you really don't need to have them in idle waiting. IF that was the case a signal diode would not work, a switching diode would not work etc.... If I'm wrong someone educate me.