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laserdj
03-08-2013, 17:49
Hi folks

A while ago I bought 2 viasho 2W greens, with lab drivers.
With less than 50 hrs of use one of them is doing very low output.

I don´t have an LPM to meter them, but the low output one is visually around 100-200mw, wont even heat my fingertip :p

Can I swap drivers and heads for testing? (they´re the same model)
If the problem is in the head, what can I look for as clues? ( it is very impractical for me to send the unit back, because of customs...)

The beam is very tight.. looks definitely TEM00 just low power

Any help / tips appreciated!

Thanks,

Bruno

sugeek
03-08-2013, 18:22
Can I swap drivers and heads for testing? (they´re the same model)


Each driver is tuned specifically for each head so don't do that. Problems could be that the driver needs to be re-tuned, a TEC is loose or dead (temperature tuning for the pump or KTP) etc... If it is under warranty get that thing back if not most tuning would need a meter so... Wait for other responses, I just wanted to note don't switch the drivers.

-Adam

laserdj
03-08-2013, 18:35
If it is under warranty get that thing back if not most tuning would need a meter so...

Very difficult to send back to China... Brazilian customs make it very hard and expensive.


Wait for other responses, I just wanted to note don't switch the drivers.

Thanks for the advice! If there´s anything obvious that I could look for, please let me know...

sbk
03-09-2013, 00:54
I don't believe it's a dead TEC as the laser should start at high power and then decrease in power, if the ambiant temp is not too high. As the Viasho's TEC only have cooling function, not heating.

Even if it's not recommander you could eventually connect the bad head on the good driver and briefly test it with analog modulation, start with low power, gently increase and see what happens. If the head is really bad, connecting another driver not perfectly matched won't hurts more...

Then if you have a multimeter you could carefully beginning doing measures there and there, but in the end the best would be to return it :(

Bbe
03-09-2013, 02:41
http://www.photonlexicon.com/forums/showthread.php/18530-V****o-DPSS-Green-has-died-need-help?highlight=viasho

In my 4w module nd:yvo4 crystal had died. For some reason, there was a crack in it. Frank proposed to replace the crystals. But for the money :D
I do not think you have a problem in the electronics, but even so worth checking out...

35212

planters
03-09-2013, 10:11
I don't believe it's a dead TEC as the laser should start at high power and then decrease in power, if the ambient temp is not too high.

I agree. Deep into a scratch build with these DPSS systems what I am learning is not to be so afraid of them. Isn't this true of almost everything? If the Vashio is a YAG rather than a vanadate, then there is more likelihood that the pump diode is temperature controlled in order to tweak its wavelength to optimize absorption. But, the operational temperature ranges for these 808nm pumps is over a 10-20 degree range, the wavelength variation for these diodes is 1-2nm and the delta for temperature is approx 0.25nm/C and so the variation from head to head will be maybe 10degrees? or less. This is an educated guess, however the point is that you are not going to explode anything with this variation by exchanging heads. Similarly, although the KTP may be temperature tuned to optimize the angle of the interaction of the fundamental and the SHG beam there are basically two classes of KTP used for DPSS lasers; those that operate near room temperature and those that are cut to operate near 100C to minimize damage from "grey tracking" in very high powered DPSS lasers. Bottom line, is that if the Vashio requires close temperature regulation to adjust this angle ( I kinda doubt this this) then the variation from head to head will be around room temperature and it can hardly get worse than it is for you already.

There may be some misalignment of the cavity optics or a dead diode (I'll bet the 2W uses two 3-5W diodes), but if the crystal(s) are cracked, at best, you would probably see some weird looking modes

The problem is that I don't know what you should do once you have tried this exchange. Whether it is the driver or the head you will need to replace/repair something and that gets back to the issue with customs. Hmm...

sbk
03-09-2013, 11:00
Similarly, although the KTP may be temperature tuned to optimize the angle of the interaction of the fundamental and the SHG beam there are basically two classes of KTP used for DPSS lasers; those that operate near room temperature and those that are cut to operate near 100C to minimize damage from "grey tracking" in very high powered DPSS lasers. Bottom line, is that if the Vashio requires close temperature regulation to adjust this angle ( I kinda doubt this this) then the variation from head to head will be around room temperature and it can hardly get worse than it is for you already.


Viasho aren't even using a specific TEC for the crystals (it's the same TEC for diode and crystals furthermore it only cools), I bet that the KTP operates at room temperature :)

But on the Viasho drivers (at least the 4W models) there's an incredible lot of adjustment potentiometers, I know the functions of the few mains but what the others are doing I'm just wondering...

laserdj
03-10-2013, 16:25
Ok guys,

I took the plunge and swapped the heads / drivers for a few seconds...
Looks like the problem is in the head. Any suggestions what to look for?
In the meantime I sent Frank an email, but no response so far.

Thanks

planters
03-10-2013, 18:23
I know the functions of the few mains but what the others are doing I'm just wondering...

Funny thing..the fan on my Vashio changes speed with modulation power and immediately not as a possible response to a temperature feed back loop. Its too quick.


Any suggestions what to look for?

Does the beam look irregular or have a larger or asymmetrical divergence?
Does it modulate normally for 0-5V input and is it just proportionally lower in output at all modulation settings?
Does warming (or cooling) the entire head while running at a stable setting effect power output?

Here is a trick. You can construct a remarkably sensitive power meter from almost any TEC (the higher its normal operating voltage range the better) and a volt-ohm meter. Use a little thermal epoxy to mount it to an aluminum heat sink (for these power levels don't worry about a fan) and cover the exposed face of the TEC with some flat black paint(high temp oven/furnace paint works well). The sensitivity is a little spooky. It will act as a bolometer and produce a detectable voltage when you place your hand within 5-6 cm of its surface. You don't need to know the actual watts of your problem laser, just what makes it better or worse. This is why calibrating your "power meter" is unnecessary.

Hopefully, Frank will be able to help because if you are on your own then you may need to "open the patient up" and it may be a little like guiding you through an appendectomy from the northern hemisphere. Oh boy!

laserdj
03-10-2013, 20:03
Does the beam look irregular or have a larger or asymmetrical divergence?

No, beam looks very nice, spot is near TEM00


Does it modulate normally for 0-5V input and is it just proportionally lower in output at all modulation settings?

Modulation seems to work fine. Also, since I have the lab driver I can lower the current and the beam becomes even fainter


Does warming (or cooling) the entire head while running at a stable setting effect power output?

I tried only warming, by blocking the fan. Head became warm to the touch, with no visible change in output.

I can try cooling it and report back, do you think it is necessary?


Hopefully, Frank will be able to help because if you are on your own then you may need to "open the patient up" and it may be a little like guiding you through an appendectomy from the northern hemisphere. Oh boy!

I hope so, and really appreciate your help! It may be useful to many others as well!