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Laser Modes

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Laserman

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Hi I am new to the forums and a little new to laser pointers. I've had my fair share of cheap $1 laser pointers and recently discovered these high end lasers. I currently don't have a laser, although my 200mW red laser should be here about Wednesday. I've been reading around on this forum mainly as well as other sites. The one thing I have seen without much explanation was laser modes. What is that? I figured it was as simple as the electricity going through the driver into the diode and back out. What are the modes? How can you tell the difference between modes? And how does a laser mode hop? Sorry for the n00bish question... lol
 





The mode is, to put it very simply, what the dot and beam of your laser looks like.

Ideally, you want TEM00, which is a perfect dot. TEM01 is two dots close together, so you have two weak beams coming out of the one laser.

Generally the higher TEM# the worse.

Laguerre-gaussian.png


Lasers mode hop (move between these modes) usually due to temperature. Do you know how a green laser works? An infrared diode pumps into a set of crystals which change the colour to 532nm (green) When the diode heats up (much like a light bulb) it shifts colour very slightly, so little the human eye couldn't tell. The crystals don't like this, and an adverse performance or mode-hopping occurs. Also when crystals expand due to heat and move around.
 
It should be noted that the above post is referring to is the transverse mode. That is, what you see when you look at the dot. It is perpendicular to the direction of propagation. Another thing that is called a mode, is the longitudinal, or resonator mode. This is essentially when you have a laser there will be a mirror on each side and there will be some exact number of waves of light between them. A mode hop (with respect to the resonator modes) is when it jumps from having 1000 to having 1001 waves between the mirrors. When not dealing with laser pointers this is generally what is meant by a mode hop.
 
Ok, wow. Thanks.

So, to avoid over heating, what would be the best duty cycle for a 200mW Maglite laser? I got it from the HighTechLazers site.
I read on the WL site that you should usually keep it on for 100 seconds and off for 10, would that be right?

And thanks again for all the help.
 
Laserman said:
Ok, wow. Thanks.

So, to avoid over heating, what would be the best duty cycle for a 200mW Maglite laser? I got it from the HighTechLazers site.
I read on the WL site that you should usually keep it on for 100 seconds and off for 10, would that be right?

And thanks again for all the help.
Click to expand...


I'd leave it off longer than that in between burns. Let the unit cool down before you heat it up again.

Peace,
dave
 
Maybe 60 seconds on, 30 off? 60 seconds is enough to burn a lot of stuff, and better safe than sorry. :D
 
Like Dave said. Use common sense, there really is no set fast duty cycle, because every laser is different, even off the same production line. 60 seconds on, 60 seconds off is a good starting point. If your laser feels warm, give it a rest.

Jase
 
If the maglite is a red burner it wont mode hop IIRC because it only has the diode, no crystals or anything, but still best to give it a duty cycle anyway so that it doesn't cause heat damage to the diode, resulting in power problems or just a broken diode altogether.

Happy lasing

Diachi
 
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