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Converting Spectra Physics ZLM Laser Head to 532NM (Part 0, initial pumping)

brianpe

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I've wanted to build a high powered DPSS green for a long time and won an eBay auction for a used Spectra Physics ZLM laser head. This head can do about 10W of 1064 and my intent is to convert it to green, or failing that strip it for crystals and optics and build my own.

But first, I have to pump it and get it to work before I start ripping into it. And therein lies my first of many questions to the forum. The head accepts two fiber coupled pump diode inputs, one on each end of the resonator. Spectra Physics uses FC fiber couplings designed around their FCBar diodes...which I can't find anywhere. The majority of diodes I see, both new and used surplus seem to use SMA connectors.

I've been looking for a high power fiber that has SMA on one end and FC on the other. I've found SMA to FC adapters, but they are designed to mate two fibers and I don't want the efficiency losses and waste that would imply. Options for me in order of preference:

  • Find diode arrays with FC connectors for a reasonable price, where "reasonable" would be around $400us/diode or less.
  • Find a high power SMA to FC short fiber. Thorlabs makes a high power SMA/SMA fiber for around $160us but I have't see a fiber offered with different connection styles.
  • Replace the FC coupler on the laser head with SMA. I don't have the head yet so I don't know how feasible this is. I know the couplers on the laser have collimation optics; I don't know if they could be mated with a different connector. I've seen connectors with collimators built-in, but would need to match focal lengths for input to the vandinate.
  • Two fibers, SMA / FC converter. Undesirable, but would work as a test.
  • Just shine a light in there and hope for the best.

Ok, that last one was a joke.

Am I barking up the wrong tree here? Thanks in advance for any ideas.
 



brianpe

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Oh, that's perfect. Prices aren't even that bad for a custom patch. Thank you.
 

Alaskan

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Man do I have a data dump for you:

Kevin at Starlight-Photonics drew this for me showing the Spectra-Physics ZLM Z-fold beam path. I just received this photo and drawing yesterday:



I bought the other two ZLM 1064 nm heads he had last month, want to do the same thing. Recently I have been able to find 40 watt 805-811 nm Coherent FAP800 lasers for under 200 dollars, they pop up every now and then but usually at twice that price. Look for modules which are made for Coherent Avia lasers, I can pass on three fleabay sellers who get them from time to time buying surplus from Coherent.

Here's a photo of the output pattern of the last FAP800 I bought which had some dark fibers, the seller replaced it for free though letting me keep this one. I just received the replacement yesterday and have not checked it yet. I used the back side of a laser power meter head as a power dump to take a photo of the beam produced by this FAP, you can see the dark side on the lower right where there was little to no output from those fibers. Even at a fairly low output (2.1 VDC @ 12.6 amps) without a heat sink I had to be quick taking this photo so the unit could not get too warm.

For this photo I used a short glass cylinder with the beam shot through it end to end in front of the FAP output, not a collimator. When using a collimator you would not see the pattern this wide so close to the FAP, with a collimator you would need to shoot the beam on a wall or something 15 feet away to allow the beam to expand enough (due to its high divergence) to see the individual fiber outputs:


Note: On the back side of the LPM head those small dark spots are threaded screw holes. In this photo you can see 14 bright spots from the good fibers, five of them on the bottom right side dim or completely dark.

For the above photo showing the FAP800 output, a small glass cylinder was mounted in front of the fiber output with the beam shot through it end to end, not a collimator. When using a collimator you would not see the pattern this wide close to the output of the FAP and would likely need to shoot the beam at a wall about 15 feet away to allow the beam to expand enough (due to its high divergence) to see the individual fiber outputs. The photo taken with an iPhone which has an IR filter in it. Regardless of the filter, the power output from the FAP was high enough at a few watts for the IR spot to be detected.

Buying surplus is the only way for most hobbyists to afford these units but sometimes they have a few dark fibers, the last one I bought had about 1/3 of them dark which is probably caused by burned out fibers or perhaps bad diodes in the bar or diode array inside the FAP but with the pattern dark all on one side like that I suspect a fiber problem. Due to this kind of failure being fairly common among surplus finds, see if you can get the seller to guarantee no dark fibers so you can return it if you don't like it. To see if they are dark put a collimator in front of the FAP SMA output connector and use a camera which is sensitive enough to 800 nm to view it on a surface.

Here's a photo of a setup to see the dark fibers I did a few years ago, this uses one of those SMA collimators out of a surplus 473 nm medical laser projected onto a wall about 15 feet away where you can see one of the fibers is dark in the bottom right side of the beam pattern. The photo against the lens face was taken at very low output power just above the lasing threshold, but far enough above it to light all of the fibers, if they were good. The photo taken of the pattern on the wall was at a few watts output:



Below, the 12.7 mm diameter PCX SMA collimator I used with the FAP for the above photo. The lens in it has no AR coating I can see and is not a good choice for use at full power output, one member had the output of his FAP800 burn due to back reflection.





Only thing is when buying these FAP modules surplus is sometimes they have dark fibers, the last one I bought had about 1/3 of the fibers dark which is probably caused by bad diodes in the bar array inside the FAP and why it ended up on the surplus junk pile. Due to this problem being fairly common, if you get one from a surplus seller try to see if they will guarantee no dark fibers so you can return it if you don't like it. To see if they are dark put a collimator in front of the FAP SMA output connector and use a camera which is sensitive enough to 800 nm to view it on a surface.

Below, modules which look like this are often 805.5 to 811 nm and were made for lasers like the Avia with a nice TEC inside to keep the FAP at the correct temperature to produce 808 nm.


Fiber cables here too, this man is retired but made these for a living when he was last employed:


Is this FAP trash or ? https://www.ebay.com/itm/Coherent-FAP-800-813nm-40W-Laser-Diode-Fiber-Array-Package-/174040896502 - I don’t know this seller.

Edit: Here's another thread on powering a FAP: https://laserpointerforums.com/threads/calling-all-fappers-fap800-precautions-and-driving-advice.104635/
 
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paul1598419

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Chris, are you any closer to building a 532nm laser from these? I know you've been looking to do this for some time. I would like to look into your progress on this so far.
 

Alaskan

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Yes, you are pointing out I've been working on this a long time and not actually doing it, I am near critical mass to get moving on it soon, just received the hosts from Vietnam I want to mount them in yesterday.

I am closer and closer, I have all of the main parts several times over, not just these, several other 1064 nm producing cavities as well as TEC temperature control modules for the laser diode and various heater mounts for a few different sizes of KTP crystals which I also have in hand to see which one works best.

Edit: I don't like to start a project without lots of options.
 
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paul1598419

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It's time to see if you can make one work outside of a host. Take that plunge! We learn much more from our failures than our successes.
 

Alaskan

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Preacher! I'm in the choir! Some of the photo's I posed in this thread are recent, in the last few days. That's evidence I'm working on it :)
 
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brianpe

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Awesome data dump, Alaskan, thanks! I bought two 40w FAP 800's from this post...so I hope they're not trashed. We'll find out:

And +1 on the link to powering them. I haven't sourced a power supply or cooling yet. Eventually I want to build a board that handles power + tec control that's all under software control. This chip looks like the ticket: dual output, analog current control through a microcontroller interface. Should be able to scale up to the gobs of current these things take:

But I will need something to fire up these FAPs just to see what condition they're in. Still waiting on them to arrive, and new goggles, since mine aren't good for IR.

BTW been very impressed with Starlight Photonics. They actually know what they're selling.
 




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