Why are laser dot shapes diffrent?

[OutlawKing]

Why is my 1W blue dot shaped as a rectangle and not circular. Are all 445nm like this?

 

[ARG]

It's because the diode is multi-mode rather than single mode. There are lower power 445's that are single mode which will give you a circular dot.

 

[SerpantSlayer]

its because they are multi mode diodes. there are single mode diodes out now that have a circular dot, however they cannot be pushed as far as multi mode 445nm diodes

 

[OutlawKing]

Ok gotcha, what is the difference/purpose between a multi mode and single mode diode?

 

[Blord]

Multi mode can deliver more power than single mode.

 

[rocket689]

Think of a multi-mode diode as a few single-mode emitters lined up in a row inside the diode can.
Each emitter gives out so much power and the sum of all the emitters makes the diode as a whole more powerful.

As far as purpose, the multi modes don't need a clean divergence/dot in the application they are used.
In the projector that they are utilized, the diodes are flourescing a phosphorescent disc to make green light.

 

[pullbangdead]

Laser dots are different shapes because lasers are different shapes, simple as that.

Think of a multi-mode diode as a few single-mode emitters lined up in a row inside the diode can.
Each emitter gives out so much power and the sum of all the emitters makes the diode as a whole more powerful.

Incorrect. It is still a single emitter, but the emitter is larger, allowing multiple modes to exist. The larger emitting area allows more power, but it's still just one, not multiple.

As far as purpose, the multi modes don't need a clean divergence/dot in the application they are used.
In the projector that they are utilized, the diodes are flourescing a phosphorescent disc to make green light.

This is still correct though, in this case the lasers are just an efficient way to make a lot of blue light.

 

[OutlawKing]

Ok thank you all for the lesson i now understand more about the modes

 

[LaZeRz]

Incorrect. It is still a single emitter, but the emitter is larger, allowing multiple modes to exist. The larger emitting area allows more power, but it's still just one, not multiple.

He was just giving a simple way of explaining the shape of the dot and the reason they can output more.

 

[jimdt7]

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Very well explained by all of you guys !

Jim

 

[BKarim]

in monomode the shape of the "dot" depends on the shape of the pump laser, on the shape of the lasing medium, of the semi-transparent mirror (on the exit face of the crystal) from where the laser exits.
if the mirror were star-shaped, you would get approximatively a star-shaped dot.


in multi-mode things are more complex due to the interferences between ligth rays.

445nm lasers are made of several crystal in line in the same diode.

naturally, all that i've said is very simplified

 

[aryntha]

OutlawKing -- (since it seems it wasn't answered) -- just FYI, yes, there are single mode (dot shaped) 445nm lasers, but they're significantly lower power. We're seeing them at 50-80mW now vs, well, 700-1000mW.