Opnext HL6545MG Diodes

[The_Doctor]

According to the specifications in the pdf file the lens can be used from
635 - 850nm.

True, but that might be uncoated. As Marconi said, some firms have them in more suitable wavelength AR coatings than others. Even the uncoated ones lose only 10%, so unless you're getting nice multilayer dielectrics for broadband AR, they're still good as a general purpose lens. Getting them coated can make the cost rise tenfold. If that makes the difference between 180 mW and 200 mW it's probably satisfying to go that extra distance, but you'd have to buy a lot of them to make it cost effective, or get into a buy that someone else is already doing.

Thicker beams are not really a problem, I would like to use a "inverse" beamexpander after the combiner cube.

I like starting with the best thinness and lowest divergence possible. If you try to fix this later in the proceedings, the optics cost and complexity rises badly.

What will be the difference between an acrylic and glass lens in our application?

As far as I know, not much. Acrylic is a very transparent medium and moulded acrylic aspheres are extremely good optically, not just good for the money. The main weaknesses are a limit to maximum power, but they're good for at least 250 mW each, I think, and the other weakness is that heat changes their focal length enough to threaten fine collimation settings. On the other hand, that bug can be a 'feature' if you design for it, you can use small changes in temperature to fine tune the collimation without complex electronics or mechanics. It's also easier to damage them while cleaning them, but in a sealed combiner you won't be doing that often.

[PNjunction]

Cool info, Doctor. I had the impression that acrylic was worse than that.

Couple questions for ya'll since I don't know much about optics yet.

One... would a wide, but low divergence beam help or hurt long distance visibility for night time sky pointing?

Secondly, before I go off half cocked, thinking I know what I'm talking about and spending $40 on a lens/case, is the MI linked to in my above post worth the money for my purposes? The intended uses would be essentially outdoors at night, and doing stupid Youtube tricks. I do like the easy change focus, but already have a plastic lensed Aixiz that does that. Any opinions on that Meredith LDC-2?

[marconi]

Cool info, Doctor. I had the impression that acrylic was worse than that.

Couple questions for ya'll since I don't know much about optics yet.

One... would a wide, but low divergence beam help or hurt long distance visibility for night time sky pointing?

Secondly, before I go off half cocked, thinking I know what I'm talking about and spending $40 on a lens/case, is the MI linked to in my above post worth the money for my purposes? The intended uses would be essentially outdoors at night, and doing stupid Youtube tricks. I do like the easy change focus, but already have a plastic lensed Aixiz that does that. Any opinions on that Meredith LDC-2?

Acrylics are great lenses.. Ive actually used them up to several watts without any adverse effects. Just as long as I choose the correct lens. In fact I have several SDL diodes that have them attached to the front of them.

Yes, A wide low divergent beam will be very good for long distances but dont go too wide as you wont be able to see the beam. But if you want a small spot size at a great distance, this is what you sacrifice..

That LDC-2 is a great lens. I expect it to only have 3 percent loss..
As it is AR coated , But I would email them and ask at what wavelength they are coated at.
I have tested them and they seem coated for red. I have actually used them in my first prototype dual red unit.
Transmission was approx 95 percent but thats the extent of my testing.

[SenKat]

You BET they are ! Not sure of the exact specs - but they are visibly brighter than the "normal" 18x diodes....

[dave]

What size beam were you getting from the ldc-2 Marconi?

[marconi]

Hi Dave
using a Mitsubishi 80mW diode...
Measured aprox 1.75 x 2.75mm beam diameter 5mm from the front
of the lens
spot size at 16ft aprox 2 x 3mm

[steve-o]

The intended uses would be essentially outdoors at night, and doing stupid Youtube tricks.

Sounds cool. Don't get busted tho.. No airports nearby I hope

[PNjunction]

Thanks for the answers, guys. I perhaps had the mistaken impression that a wider beam might be more visible over long distance because of it's width, and also because the higher NA would make up some of the difference by letting more light through.

Hey, imagination is fun, even when it doesn't correspond to reality.

OK, so to see if I'm getting the idea... given the same diode, a thinner beam will be more visibly intense, even though the lens' NA might be slightly less efficient?

My primary goal is for the most visible beam across the night sky. The stupid Youtube tricks are a very distant second, and can already be done using another Aixiz that's already up and running.

[PNjunction]

Hehe... should be fine, Steve-o. My location does triangulate with two major airports nearby. However, I'm extremely careful both indoors and out in selecting where a beam will go, what it may terminate on, and keep very aware of all environmental factors such as planes in the sky, looked up federal and state laws, etc. I even wait for weather patterns to cause planes to approach from a different direction, leaving the sky above my area virtually traffic-less. Years of handling firearms has made such safety practices second nature.

Additionally, I've got my noob, greenie owning friends scared to even put the batteries in their lasers... lol. So, now that I've provided my safety credentials...

[The_Doctor]

OK, so to see if I'm getting the idea... given the same diode, a thinner beam will be more visibly intense, even though the lens' NA might be slightly less efficient?

Yes, but there is reason to enlarge a collimated beam if you want high visibility of the beam, not just the distant spot. Even a 0.5 milliradian beam from a 1 mm width at aperture is going to spread a bit after 500 yards. If you made that beam enlarged ten times, it won't be a fine bright needle, but it will still be a damn sight better at 500 yards than it was. Start with the best collimation you can get, no matter what, if going for long range. In practise this means use a wider, longer focal length lens to make the wider beam. It's easier to set and keep the focus optimal, and it reduces the optics you'll need later, if any.