Singele / Multi mode?

[MrMcChicken]

What is the difference between single and multimode diodes? I read it all the time but i doesn't know what this mean.

 

[DrSid]

In simple terms it refers to shape of the beam. Single mode is nice round dot with clean maximum in the middle. Multi mode is usually wide ellipse, or even rectangle, often with several maximums. It is usually result for different diode construction. To achieve high power, the active region is made wider, which then allows light inside to resonate in more then one path.
Single mode diodes are used where beam quality is important, like DVD or BR.
Multimode diodes are used where output power is important, like projectors, or IR communication diodes.
Multimode beams are problematic to focus at large distance, because they have different divergence in each axis.
Green DPSS lasers also can have more modes, but they are usually not so prominent.

Also interesting reading: Transverse mode - Wikipedia, the free encyclopedia

 

[MrMcChicken]

Ah, okay thanks +1 :beer:

 

[Things]

This is the output of a single mode diode:

And multimode:

Notice all the lines and how it generally looks a lot messier? This is because the diode is running in a different transverse mode, thus using more of the cavity. The result of this is the beam is an irregular shape.

 

[MrMcChicken]

seems that there is really a huge difference . Thx a lot!

 

[Things]

There is, but that is a raw diode output (No lens in front) You don't notice all these lines once you have focused it down into a small beam. The only difference is a single mode diode will have more of a round beam, whereas multimode will look more like a rectangle.

 

[TheReddish]

is that one of yours, I have never seen a 445 wigging out with that much interference it looks kinda sweet for being a mess.

of was it something you camera did to it.

 

[Blord]

That is a normal output of a 445nm diode without a lens.

 

[TheReddish]

I dont see them lines on mine with my eyes, I see 3 lines with my eyes, but not 50 and I don't see wings either with the lens out, just a long oval with 3 lines. or to edit, I don't see the interference in the fast axis radiation

 

[DTR]

They will vary a bit and depending on the current the lines may or may not be as defined. Here is a picture I took of a M140's raw output.

 

[TheReddish]

ok that is more like what it looks like to me, you still got a wing on the left, I have not pushed an a140 or M140 past 1.4a yet so maybe that has something to do with it. I just was commenting on his fast axis radiation or the darker blue on the outside, the interference pattern looks very irregular to me and was wondering if it was something to do with the way his camera saw it.