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What is a mode hop?

Book

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Just as the title suggests, what does it mean that a laser is mod-hoping?

What is causing it?

How to cure the situation?

Thanks!
 

apex007

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My X105 sometimes starts out in TEM01. But after a little warmup the beams snap back together and burn the heck out of everything. Usually only happens on low batteries. It's fascinating to see two perfectly parallel beams coming out of the same aperture.
 

VW

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Ah, would a laser that randomly projects a ratiated patern as well as a beam be concidered as, mode hopping?  

Nice! I see the jpg now. So, is there any indication in which the states damage or threat the diode?
 
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mode hopping cant be fixed, the diode wont work correctly despite what you do.
it can switch back to tem00 and go to tem01....02...etc.


damn we should've added this to the FAQ earlier :(
 

MarioMaster

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it's only a problem with DPSS lasers and most likely comes from misalignment of the crystals or defects in the crystal itself, when i was repairing my 200mw green module, slight angles to the crystals could shift it anywhere from TEM00 to TEM30

it doesn't damage the diode or really anything, it's just a non desired output
 

climbak

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there are also longitudinal modes that arise from the size of the laser cavity. As it heats up, the cavity will expand and the mode will hop to a different one. For diodes especially, the short cavity length sometimes causes there to be multiple modes lasing at a given time because the bandwidth of the gain medium is broader than for say a gas laser which usually has a much longer cavity length.
 

Zom-B

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How can I reliably detect which TEM modes are in my beam?

For example, I have a green that is apparently multimode at very low currents. It shows a beam profile where the left half is brighter than the right half.

I also have another RED which produce a pattern identical to this:

Is it also multimode, an if so, would it be a mix of very high TEM's (from the other image on wikipedia) ?
 




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