Where to put the a pin hole aperture for better beam profile

[Fotobysw]

Hi diode experts ;
I have this topic on the 445nm area but I thought I would try here too.

I was wondering if anybody knew the best place to mount a pin hole aperture to profile the beam to a small dot.

I have a 9mm 445nm with the G2 glass lens from DTR running 2.9 watts on 2.45 amps. It runs at a constant 30% C for hours with my TEC setup pictures below. I have tested the pictured set-up for 14 hrs at the above specs with no drop in wattage or rise in temp.
I think I can get about 1.5-1.9 watts from the 638nm red diode with the same set-up.
Both these diodes were bought from DTR with his G2 lenses.

So where is the best place to put the pin hole aperture?
Should it go in front of the lens or after the lens?

I am building a 4-5 watt 3 diode graphics projector with TEC on all diodes and I want the best profile before it hits the scanners.


Thanks for the help
Fotobysw

[Picasso]

Most projectors I've seen on this forum do it at the scanner. Some with cardboard.....

[badger1666]

Cardboard ?? You are joking right! Clipping high power beams with cardboard = fire!

Most projectors I've seen on this forum do it at the scanner. Some with cardboard.....

[-bart-]

In fact the galvos themselves are a masking-aperture. A masking-aperture is something different than a pinhole. Optically you can't just shoot a beam through a round hole and expect the beam to become round over its entire path. It doesn't work that way.

Forget round beams, a square beamprofile is sufficient for graphics.
You can achieve this by prismpair or by cylinder lensset.
Matched divergence is much more important than beamprofile, both for graphics and beamshows.

If you insist on a round beamprofile, correct the beam to a square then run it though a kepplerian telescope. Put the pinhole at the focalpoint of the telescope. Expect at least 50% losses at your first try.

[LaNeK779]

especially this particular red one will not benefit at all by the addition of just a pinhole. the mitsu beam characteristics are tough to deal with.
you need a shorter Focal length lens, a diode mount that allows centering the diode to the lens and a cylinder lens pair. then you can start talking about whether a pinhole / apperture etc is appropriate

i just reference your other thread here, to keep it all in one place http://www.photonlexicon.com/forums/...e+beam+profile

[planters]

I have this topic on the 445nm area but I thought I would try here too.

I'm chasing you around here. Check out your other thread.

[buffo]

run it though a kepplerian telescope. Put the pinhole at the focalpoint of the telescope. Expect at least 50% losses at your first try.

This is the exact advice I was given by an optical specialist (PhD) from Semrock.

A Keplerian telescope (or more correctly, a 1:1 Keplerian collimator in this application) is a pair of identical lenses (double-convex or plano-convex) that are positioned exactly twice their focal length apart. The pinhole goes in the middle (at the focal point). Then, as you move the pinhole closer to the first lens, you begin to "carve out" more of the beam. You lose power, but you get a smaller beam profile. Divergence should be unchanged.

Bonus: the light that diffracts around the edge of the pinhole should miss the output lens completely (assuming your lenses aren't stupidly large), so you won't have a "halo" around the beam.

Adam

PS: While it looks great on paper, I must admit that I've never actually tried it in a projector. It's on my to-do list though...

[mixedgas]

A Kep telescope is a nice shot if you use long enough focal length lenses. However keep in mind that if the die is not emitting a profile that you like as one of its transverse modes, a shaped hole may not help you much. I've tried this, and I've had sucess with hand selected devices. Dr Lava's lens set is the best solution I've seen so far for 445

Steve

[planters]

See the video I made showing the spatial filter in my new projector project.

Steve,
What I have found is that at these very long FL (ie 100mm) the focal spot is almost macroscopic as in probably greater than 100um. Building up a stop (pin hole) to approximate the shape of the far field spot and hence the shape of this preliminary focus is easy and cheap.