Where to put the aperture placement for the 638nm and the 445nm diodes

[Fotobysw]

Hi diode people;
I was wondering if anybody knew the best place to mount an aperture to profile the beam to a small dot.
I have the G2 lens on both the 445nm and 638nm that was provided with the auctions.
So where is the best place to put the 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

[LaNeK779]

(sorry for the oversimplified approach, I prefer to keep things simple. And i sure hope more knowledgable people chime in on this

well, assuming that no other optics are used, i would place the "apperture" (a round hole acting as a beam mask as i understand it) as further away as possible. For example, just before the beam hits the dichro optic. I will risk to say that a "pinhole" is what you want to implement and not an "apperture"

This is only a "demi-fix" for a beam shaping application.

A good way to go with the 445nm diode would be to add a pair of anamorhic prisms in front of the g2 lens. Anamorphic prism pairs can be found here http://shop.stanwaxlaser.co.uk/anamo...-red-311-p.asp and here http://lasershowparts.com/store/index.php and the general theory behind how they work can be found here http://www.edmundoptics.com/optics/p...specifications
I only suggest the use of prisms, as they are easier to work with than cylinder lenses, at least for me

After all these optics, the use of a pinhole would yield better results.

The same goes with the 638nm diode (although more info would help). If it is the "mitsu flashlight diode" then the best results so far have been found to be with a 2mm lens and a pair of pcx and pcv cylinder lenses. Search around here, there is tons of posts available on this (http://www.photonlexicon.com/forums/...lashlight+fail). If it is a single mode red, then maybe no pinhole is needed, as beam properties of these diodes are much much better. Most probably, even any form of secondary beam correction (anamphics or cylinder lenses) should not be necessary with the g2 lens.


To make things more complicated, the best way to really correct (actually clip) the beam shape is to use two equal lenses forming an 1:1 telescope and insert a very very small hole (definately less than 0,5mm) right into the focus point. This should have the ability to be micrometrically manipulated on two axis for precise adjustments. This tiny hole can be refered to as a "spatial filter" and you can see something vaguely similar in action in the pic below. The results are surely worth the trouble




ps. i suppose you are not building a 4-5watt 3 :diode: projector, as there is no direct green diode at that wattage available (at least to hobbists)... so it should be two diodes and a dpss green. And that means a hell of an overdive for the red diode... may i suggest you settle for 500mw of red, 500mw of green and something closer to 1w for 445? or for an 1:1:1 power ratio?

[Fotobysw]

I was trying to get around adding more optics. 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. And yes I am using a 500mw-750 DPSS 532nm green. My problem is that the best lens that DTR has still gives a square beam on the 638nm and a rectangle on the 445nm. What I want to do is to focus the lasers through a pin hole and chop the beams so I can have the best beam shape at the scanner mirrors. If I have to add more optics then I guess I will have to bite the bullet and do it.
Thanks for the help
Fotobysw

[planters]

Nice plan and a good set up. Usually the best shape at the scanner (common mirror dimensions) is a square that is slightly smaller than the width of the mirror at a 45 degree AOI. With high powers and single diodes your set up is well suited to a spatial filter. To keep the design simple, I would preform the beam shaping/expansion for each diode prior to the spatial filters then tweak the size of the square shaped beams with a low amplification positive/positive telescope (Keplerain). The longer the FL of these positive lenses the larger the focal spot and the depth of field tolerance. The better way to filter at the focal plane is to clamp thin blades while leaving a gap than to use a commercial round pin hole ( hard to size and the wrong shape). Place the filter slightly inside the focal spot. I don't know why, but it works better. And set everything up; all the way from the diode to an actual test scan and THEN position the blades.

I am running two projectors with this kind of system and it works well. I keep breaking my promise to post this build due to other priorities, but as soon as I can you'll see this demonstrated.

[LaNeK779]

hey eric, just a quick and dirty pic of this specific arrangement would do for now

it's been a while since i last admired your work and i have missed it a bit (a big bit)

[kecked]

yea what happened? bump.

[Fotobysw]

I used a lens that DTL provided with the 9mm blue and got the red focused down to a pin point. That seemed to work fine. I am now putting the projector together. Filed the variance's Friday. So we are doing good. I will post the pictures of the system when done.