Polarisation, Knife Edge & V/H ??

Ive read about polarisation, knife edge and horizontal & vertical alignment but want to know more (I dont understand)

OK I need a basic explanation of what polarisation is, is it a relation to the laser or the optic or both and what is going on during the alignment/combining of 2+ lasers. Is it carried out just to get max power from the laser.

What is knife edge alignment?

And what is being discussed id someone is talking about horizontal & vertical orientation.

Can you align (get correct polarisation?) lasers through optics without a LPM and if so how?

Sorry for all the questions but all the answers I have seen so far go into deep physics and I just need some simple explanations.

Thanks

Here's a way to think about polarization that isn't necessarily accurate, but results in a mental model that works for most uses.

Picture a photon traveling towards a window with venetian blinds. Now remember its wave nature and how as it's traveling towards the window in a straight line, it's waving back in forth perpendicular to the line of travel. As it reaches the blinds, if its wave is in the direction that will slip through the lines between the blinds, it'll pass through, but if it's perpendicular, it can't slip through the blinds and will bounce off. So horizontally polarized light will pass through a horizontal polarization filter, while vertically polarized light will bounce off. BTW, If you shine a beam with polarization at 45 degrees, half will bounce off and half will pass through. The part that bounces off will then be vertically polarized and the part that passed through horizontally polarized.

As I said, this is a very simplified model. See wikipedia for what Photon Polarization really is.

A PBS cube will reflect light of one polarization and pass light of the other polarization. You can use this to overlap two beams with polarizations that are at right angles to each other. To get maximum power a LPM would be helpful, but you can eyeball it decently. Let's say you're doing the pass through beam first. Shine it at the PBS and rotate. As you rotate, it'll go from all reflecting to partially reflecting and partially passing through, to all passing through. Just stop when it looks like it's all passing through and very little or no light is being reflected. Then do the same with the reflect beam.

You can only combine 2 linearly polarized beams this way, as the resultant beam will have random polarization and if you try to pass it through another PBS, only half will go through.

To "combine" multiple beams, people actually place the beams right next to each other so it looks like one beam, but fatter, then use optics to shrink the beam back down at the expense of worse divergence. They use knife edge mirrors to do this. Bounce one beam off a mirror right at the very edge and pass the other beam right by the edge of the mirror so that the two end up beside each other.

Some people knife edge a bunch of vertically polarized beams into a fat cluster of beams, do the same with horizontally polarized beams, then combine the two clusters with a PBS, then shrink it down.

This is all for combining beams of the same color. If you want to combine different colors, you can also use dichroic filters, or dichros. These are mirrors that reflect one color and pass through other colors.

Thanks Max thats a good enough and clear enough answer to deserve a bit of rep:gj:


Cheers

Well said!

Thanks Max for the great explanation!
-Robert

heres some info which you may or may not find useful.

knife edging is just aligning two beams parallel.

what i did in my 5 colour projector build is knife edged two 660 open can reds into a cube. i then put my 635nm module into the cube.

i set the 660s polarisation the same, but at 90degreed to the 635 beam. due to the size of the 635 beam i could easily fit the two 660 beams inside it using a cube.

heres are some pics which might help you understand

Thanks Andy,

On a side note, I got a Red PBS cube that I will be using soon.
I see you have arrows on top of yours, are the cubes designed to have beams coming in on a certain 2 sides or would it work just as well if the beams entered on the opposite 2 sides?
Mine isnt marked?

i marked mine just to make my life easy.

you can use any side you want it makes no odds, you just have to turn the laser so suit the side your using.

im on my phone at the moment but go onto my site theres a guide there with a vid on how to use a cube

Lovely stuff....cheers

home now, link

Laser Man - POLARIZED CUBED BEAMSPITTERS

you can see in the pic how the laser beams look without lens on, they are different shapes