200mW DX DPSS dying?

[dnar]

Hi All,

My 200mW DX DPSS looks like it is dying! It has run in a heatsink for many hours, but last night it suddenly went very dim.

It has always consumed 650mA at 3.0V, it is now consuming 800mA. Weird. The IR diode is working, I checked. The green beam is very dim, only visible up close.

When I first power it on, it is bright as normal for only 1 second, then it goes very dim and looses TEM00 (4-5 small dots).

I suspect the krystal is @&#^ed. I have tried adjusting the pot, carefully. Starting at 200mA and slowly moving up to 700mA, the beam appears normal around 650mA and then goes dim again.

When I first got this laser, I did think 650mA was a lot of juice...

In the mean time, I am using the identical 50mW unit bought from DX in the same shipment. This 50mW has much better beam profile than the 200mW, the 200mW also produced it's beam way off center (near the edge of the final collimating lens).

I have a number of other 30-50mW 532's, I was considering a krystal transplant (ambitious yes!) but I suspect the smaller units won't have krystals to match this awesome 200mW unit. When healthy, this baby burnt matches and black plastic.

Oh well, if all is lost, it was only like $50 on DX. I really would like a good replacement so I may continue experimenting with building my own scanner....

All advice welcomed.

 

[goninanbl00d]

Yeah, either your crystals or the pump diode is probably fuxx0red. The same happened to my green module one day out of the blue.

If your beam drops suddenly in output power, it's probably a damaged crystal. Chances are the module was never designed to take such a large amount of power, and was a 50 or so mW which had overpumped crystals, which would have damaged them over time.

The crystals themselves are tiny- less than 1x1x1mm square- and there's no way they can sustain such large amounts of power without being damaged. So a transplant won't help. You'll want a proper high-power modules with crystals which can sustain such large amounts of pump power without being damaged (thermal stresses, coating damage, misalignment). A lot of things can go wrong, and it may not be your fault either.

700mA isn't a lot either, considering that the pump diode is at least 1W for it to even come close to 200mW of green output.

Hope this helps, and sorry to hear about your loss.

 

[dnar]

Thanks.

Well with nothing to loose, I dissected the laser. The crystal surface (LD side) is burnt...

R.I.P.

 

[goninanbl00d]

Burnt?

"Well there'sh ya prublem!"

At least my crystal surface still had the coatings on it.

Pictures? I still don't believe that the coating would have burnt off.

Also- if you're looking into a scanner, look into a proper lab laser/module with TTL modulation- it's much easier to control than any of these cheapie green modules. A 100mW labbie rated for constant duty should be around $100-150 from a reputable dealer.

But if you're still after a module:

High power 300mW green laser module/IR filtered [OLHGLM250] - $225.00 : Welcome to O-Like.com, Your source for laser products

That should have the nice juicy crystals that won't go up in smoke. Mount it on a massive heatsink and it should do fine even for constant duty cycles. It also has a 6 month warranty to top it off.

 

[Prototype]

Most <1W greens (not lab modules) use a small bonded crystal set. So the size is irrelevant, it's how hard they're being driven and their quality. Also, TTL modulation is 0V off, 5V on, not many colors, while, in theory, analog modulation provides 16,000,000 colors from an RGB laser.


Edit: I *think* on the power of modules vs. crystal set size.

 

[goninanbl00d]

That's what the crystals in the DX modules are. But they're less than 0.5x0.5x1mm all up. I don't think one of those could cope with 1W of pump IR even with a peltier- the crystal simply can't dump heat into the module's body fast enough. So even if the body appears cool, the crystals could be burning up inside without you even knowing.

For example, CNI pen crystals are usually 1 to 1.5mm wide. The PGL-III-A has crystals which are 2mm wide. The more area to deal with the power, the better.

If the crystal can't dissapate the heat, inevitably there will be thermal stress between the module and the crystal, and that will cause the crystal to distort and crack.

I'm not a scanner person, so I don't really know about different modulations[sic], but I do know TTL is better than switching the power on and off at the module's source.

 

[Prototype]

I'm not saying anything about the size, of course that matters, I'm just pointing out that they all use a small bonded set.

 

[goninanbl00d]

The bonded set is extremely crappy.

Half of mine was covered with the white bonding substance.

 

[BShanahan14rulz]

I should hope htey aren't bonded with opaque glue.... that is probalby the silicone they use to glue the crystal to the L heatsink.

I had always wondered if anybody found some nice 12mm modules that happened to have nicer crystals in them... Also wondered if there are better bonded sets to buy. Orienting the yag and then the ktp in a space that small would be difficult for me.

I had toyed with the idea of remounting the crystals with a more suitable epoxy, but why break something that works.

 

[aryntha]

Just wondering, this isn't the first post where I've seen "sudden DPSS death" ... -- is it possible that a speck of (opaque) dust landing on the end of the crystal facing the LD, could cause rapid heating and sudden failure?

 

[goninanbl00d]

Mine wasn't like that, the pump LD's die was in direct contact with one face of the Nd:YVO4.

The crystals also looked fine (coating undamaged, no cracks/scratches)

 

[JLSE]

If you have a meter to test the output, try backing off the current that the LD is seeing. The LD can go out of its required range of 808 and also cause the output to drop. Find its highest output, then back it off 20-30mW.

When lining the crystal set up, I always look for the 'sweet spot', problem is, once youve found it, if you go over what it can take from the pump, even briefly, that sweet spot goes away.

Re-aligning the set can sometimes defeat this, but only if the set has suffered no damage to its coating or cracks. And once again you are at the mercy of the quality.. You only get a couple of chances to find another 'sweet spot' if you are lucky.

IIRC I covered some of the alignment process here > http://laserpointerforums.com/f45/200mw-diy-green-labby-1000mw-pump-30923.html

Its not the same setup, but may give an idea... If you need help fixing yours, feel free to ask and I will see what I can help with.