can spatial filters be used on all the beams AFTER they have been combined?

[kecked]

Title says it all. Can you combine all your lasers and use a single spatial filter for the whole works? Seems like a nice way to ensure that you have perfect matched size beams. You might say trim a little on the blue but that would show as a blue halo anyway. What think yea planter god of optics? Can this be canned and mass built for a group buy? Thinking a few lenses and a little laser cutter time. Add your own blades.

Actually now I think of it could you not thread in a pin hole in a telescope and make a nice little spatial filter beam expander?

[danielbriggs]

With achromatic lenses only, I don't see why not - assuming all multi-wavelength sources have a similar non-ideal beam distribution.
Although this would not be a "long distance" solution, as the beam propagation would depend on the source quality (M^2).
If any sources are knife edged / stacked / or use any other geometric combination (except 2 sourced combined with a 1/2wp + PBS), then forget it.

[kecked]

just three in a row single diodes combined with dichro. will try and see what I get

[Galvonaut]

That makes a lot of sense.

Are spatial filters applies at the beam waist or some specific distance from it and if so, would each diode need to be focussed at precisely the same spot in order to apply the spatial filter?

Keith

[Jem]

Hehe... One beam through a SF is relatively easy (with a bit of practice). Two beams is *much* more difficult. Three beams is damn difficult and requires a very stable base plate and high quality optics mounts. Any expansion/contraction will make the process doubly difficult as it'll constantly pull itself out of alignment.

[kecked]

here is the website I get my beam expanders from http://www.meshtel.com/ I don't think you'll find them cheaper. I use 2x.

[kecked]

bummer. I was hoping for something off the shelf. Its just now that it's all diode there is a bit of smutz I was hoping to trim off. I thought the blue was ugly but the green has more because it is easier to see than the over spill from 445nm. The green is actually not bad but it is soooo evident.

[planters]

Daniel is correct. The best position for the apature is just past the mid lens focus and this has to be the same for all the colors. Multiple diodes (for each color) are no more difficult than aligning them in the first place. It's trivial. What might be difficult is co-aligning the three colors to the needed precision within the projector as well as in the far field.

[kecked]

that could explain why when I use these beam expander right after the collimator it cleans up the beam some. It must act like a pinhole. I'll try it on the green. I need to get a 3x for the blue and put the 2x on the green then they will match perfect. The blue is nice but it has a blue glow around the beam I'd like to get rid of and the green has wings I bet are from the lens or dirt

[planters]

The pinhole only works very near a focus. Only the most extreme aberrations will be eliminated by masking near the edge of a collimated beam.