mRad calculation

[Bradfo69]

Thanks. It sounds like they're going to send me a new green with prisms in it which may be a bit less power but a cleaner output. They may have achieved similar results to what you did but in a different way.

What I'm also trying to do here is ensure where the problem lies and make sure it's narrowed down before we begin shipping things back and forth halfway around the world.

[swamidog]

i'm been working with a 520 diode green here. in my experience, an anamorphic prism pair creates a much cleaner beam, but the losses are greater. without a prism pair, you really have to use a spatial filter.

Thanks. It sounds like they're going to send me a new green with prisms in it which may be a bit less power but a cleaner output. They may have achieved similar results to what you did but in a different way.

What I'm also trying to do here is ensure where the problem lies and make sure it's narrowed down before we begin shipping things back and forth halfway around the world.

[tribble]

Which 520 is that, swami?

Do we think the Pluto green is divergent because they were trying to fit it on to small galvo mirrors?

[swamidog]

laserwave 1W 520.

planters can answer these questions better than i can, but the trade off for small near field spot is an increase in far field divergence. for giggles, you can try putting an anamorphic prism pair in the beam path of the green module. i tried that with my green unit and ended up with a *very* nice far field spot.

TANSTAFFL.

Which 520 is that, swami?

Do we think the Pluto green is divergent because they were trying to fit it on to small galvo mirrors?

[tribble]

TANSTAFFL.

Truth.

Given that, I am wondering about the best optics train for the single-mode setup. I was thinking of starting a new thread for discussion of collimator selection and theory to know which collimating lens to buy, as good ones seem to be pricey, one wouldn't want to buy a bunch just to find the best one for any particular application. You should be able to do some math and figure out which FL collimator to use for an initial beam size of "a x b". The real mystery seems to be emitter size, but I'm getting ahead of myself, I think.

[Bradfo69]

TANSTAFFL ??? Is that anything like that popular Netherlands LEM dessert called a stroopwaffle?

[tribble]

Mmmmm, desertwaffle... sounds like something swami might have for breakfast.

There Ain't No Such Thing As a Free Lunch.

Or, you can't get tiny beams and low divergence at the same time out of a diode.

[norty303]

Just a note regarding the 'too tall' comment on the previous page.

Don't forget that the scanners flip the orientation, so when diagnosing something 'post scanners', something that appears 'too tall' is actually 'too wide' in the horizontal plane out of the nose of the module (assuming a fairly conventional projector layout, etc)

And this is why you have to adjust the opposite dichro/bounce mirror axis to what your brain tells you when aligning the beams (up/down for left/right on the wall)

[planters]

I have one of these 1W 520's that DTR sent me some time ago, but I haven't had a chance to evaluate it yet. Nevertheless, DTR's site shows the green producing a far field pattern that is very similar to the 445 diodes, only a little tighter. This makes sense as it is the same GaN junction with the crystal lattice stressed to generate green. Based on this I would treat this the same as a blue. I would use any aspheric collimator that transmitted @520 (probably many of the existing blue ones will) and then use a cylinder pair to expand the asymmetric, smaller near field dimension to reduce the spread in this dimension in the far field. The cylinder pairs work better and have lower loss than the prisms. There is no free lunch. If the collimator has a shorter focal length then the initial spot will be smaller, but will have to be expanded more to achieve the same divergence as a longer FL collimator and a lower power cylindrical expansion pair. I'm kind of surprised that the beam coming out of the blue module is still so asymmetrical in the far field if it was corrected by the prism pair.

Spatial filtering will do a good job of cleaning the dim glow and the wings from the far field, but will do nothing to reduce the size of the core of the beam. This needs to be accomplished by the collimator and the cylinders.

[tribble]

If the collimator has a shorter focal length then the initial spot will be smaller, but will have to be expanded more to achieve the same divergence as a longer FL collimator and a lower power cylindrical expansion pair.

Given those two options, are there circumstances which benefit from using the shorter or longer FL for the collimator? Or are they equivalent in practice?