Cylindrical and rectangular transverse modes

[gozert]

I've been reading a bit on Wikipedia about the transverse modes on lasers, and have some questions.

So, I've read about there being cylindrical and rectangular transverse modes. I think I know what the difference between the two is, but I don't know which mode applies to a certain kind of laser.

For example, do you get a rectangular transverse mode with a 445nm rectangular beam, or doesn't that have anything to do with it?

Could anyone explain this to me?

 

[Robert S]

Ah, really interesting , i just read through that wiki article, too, didn't understand much of it, though.
Ill keep an eye on this thread.

 

[lazeristasUVISIR]

For example, do you get a rectangular transverse mode with a 445nm rectangular beam, or doesn't that have anything to do with it?

Yup, especially with a low power. The rectangular shape is due to different divergences on perpendicular axes of the beam. With additional optics [like prisms or cylindrical lenses] it can be compensated and the beam become round
The 532-nm laser beams are quite nice round shape, but the mode is rectangular too. Sometimes these lasers have a double beam, that is TEM10.

If you read Transverse mode - Wikipedia, the free encyclopedia you should keep in mind that they take a laser resonator symmetrical and give this formula

A laser diode resonator is not symmetrical in x and y axes. Thus formula for w is dependent on x and y too.

 

[gozert]

Yup, especially with a low power. The rectangular shape is due to different divergences on perpendicular axes of the beam. With additional optics [like prisms or cylindrical lenses] it can be compensated and the beam become round
The 532-nm laser beams are quite nice round shape, but the mode is rectangular too. Sometimes these lasers have a double beam, that is TEM10.

If you read Transverse mode - Wikipedia, the free encyclopedia you should keep in mind that they take a laser resonator symmetrical and give this formula

A laser diode resonator is not symmetrical in x and y axes. Thus formula for w is dependent on x and y too.

Alright, I think I kind of get it. What I'm wondering though is, there are two images. One of cylindrical and one of rectangular transverse mode. How can I tell when a laser has a cylindrical or rectangular transverse mode? Like you said, a 532nm has a rectangular transverse mode while the dot/beam is about as round as it can get.

Cylindrical:

Rectangular:

 

[lazeristasUVISIR]

How can I tell when a laser has a cylindrical or rectangular transverse mode?

Generally it is a complicated question. In principle, a cylindrical mode can be decomposed into rectangular modes and vice verse.
Look what a math formula is "easiest" to use to define your beam and its propagation.

 

[gozert]

Generally it is a complicated question. In principle, a cylindrical mode can be decomposed into rectangular modes and vice verse.
Look what a math formula is "easiest" to use to define your beam and its propagation.

Oh I get it. Not that good with math though, and probably not going to calculate it for every one of my lasers.

Thanks however for the explanation.