Green spot problem - TEM 00 or...?

[Steve Milani]

Hi all guys

Inside my ~2.5W projector I have a green CNI module MGL-H—WL203-500.
I measured it and it give out 620mw. Good point for it.

Now the problem...
Since few days its spot goes ...crazy. I explain me better.
When at full power its spot are "double", something like this oo (two points are very close between them, but cleary visible both).
When i turn down the output power by DS3CB card (Stanwax Laser), its spot return practically to be only one ( to be sincere, there is still a very very little "double" spot.... maybe its phantom??).
I also tried to take the DS3CB card off and to control the output power by QuickShow settings. The problem is still the same, unchanged: double spot. In the air, at full CW power, is cleary visible the double ray.
Module has worked not more than 40-50 hours (bought in October 2012). When I bought it, it was perfect: single spot 3mm diameter.
Now, if I want to obtain a discrete spot, I have to reduce its power about 45-55 % (not alwas stable also...). At full power it is stable, but doubled!

Obviously I have not opened the module. I want not. I'm afraid to do something wrong.

My questions are:

1) a 500mw green module is a single or double diode module? If double diode, maybe they have gone out of alignment?
2) Maybe module has gone from (near)" TEM 0" to "TEM 00" ?
3) ???????????

Any advice/help is more than welcome

Thanks and forgive me for disturb.

Greetings

Steve

[steve-o]

Green DPSS lasers do some strange things .. maybe the xtal has heated and cracked or become out of alignment with the pump diode? Just guessing here until the experts arrive ..

[mojo]

Have a CNI MGL-III 300mW unit having similar issues. After some months the maximum power went down by around 25% and with higher currents the laser jumps from TEM00 to TEM01.

also modulation is like hell - starts to "flicker" for some seconds before getting stable. Does this still work with your unit?

have already triedto adjust the temperatures - no success, also the crystal coatings etc. do look quite fine.

[kitatit]

Hi Steve,

I can't offer much of an explanation to why this is happening but the phenomena is called mode hopping.
Have a look at which beam mode it is hopping too.

https://www.google.com.au/search?q=i...iw=568&bih=268

While you are waiting for the experienced guys spot this thread, try doing searches on reasons for a mode hopping green.

Question 1. It will only have one pump diode so this is not the problem.

Question 2. Yes I think this is what has happened ( it's hopping from tem0 to tem10 or tem1.

I had this happen on a CNI OEM pointer core. I was hoping to use it in a mini projector with passive cooling.
It started behaving in a similar manner at to what you'd described.
I ended up using a small TEC cooled Lasever instead.

Good luck and fingers crossed.
Kit

[Steve Milani]

Thanks Kit.

Now it's all clear to me.
I looked at TEMP table which you have linked me and I compared with my green beam. I've clearly seen the shape of my beam: it is like a very small vertical strip instead of a circle.
Module has gone to TEM 01. No doubt about.

Thanks once more for detailed infos you kindly gave me.

I want NOT to say bad about CNI.... Maybe I've been unlucky only... But next time I'll buy modules from other factory

Greetings
Steve