D i v e r g e n c e

[Alaskan]

If you start out with a single mode TEM00 laser diode and want the tightest divergence possible, how is that done? Does the size of diode chip alone determine the end result (without using a beam expander lens arrangement)?

From what I've been able to determine, divergence is king as a 100 mw single mode laser focused to infinity will produce a much smaller spot and even though much less powerful, a much brighter concentration of energy at distances of over 100 meters than most, if not all 2 watt multi-mode pointer lasers with the same focus.

So my question is this, what can be done to minimize the beam spread or divergence of a laser pointer, other than using a beam expander? Will the type of collimator lens help?

Thanks, appreciate any ideas you can share with me as I am in the process of building a single mode laser pointer.

 

[Rifter]

I have looked into this a lot lately as I am also obsessed with a tight beam. The only way so far I have found to do this is with a beam expander unfortunately.

Subscibed though incase you figure out another way.

 

[Cel]

Some have used cylindrical lenses to make the wide beam of multimode diodes more squarish. But I don't know whether you can improve the divergence of a singlemode diode though.

I heard using the correct lenses with the correct diode/wavelength produces better quality beam but I am not sure which lenses (acrylic, 3-element) go with which diode/wl (520nm, 405nm...).

Which diode are you using?

 

[upaa27]

I have heard that fast axis collamination lenses can focus a diode bar to infinity which is a major feat. Look into it.

 

[Cel]

I have heard that fast axis collamination lenses can focus a diode bar to infinity which is a major feat. Look into it.

Yeah, but he is doing a single mode build...

 

[Cyparagon]

Will the type of collimator lens help?

Yes, you can choose a larger lens with a longer focal length, but this has the same effect as a beam expander. Example:

There's really no other way to improve the divergence of an existing diode without changing the beam size. Sorry.

 

[Alaskan]

Thanks, this is very helpful, knowing the limits is what I needed. The larger lens with a longer focal point sounds good to me, I don't need a tiny thin beam for what I want which is extreme throw, to borrow a term from flashlights which can't hope to compete with a cheap laser. That's the answer for me then, a longer focal point to give the same reduction effect that a beam expander has without the loss of adding more lenses

I'm becoming obsessed with minimum divergence myself.

 

[Shakenawake]

the thing about beam expanders, they improve divergence at the cost of beam width, it's unavoidable as cyp said. beacause the beam is diverging less quickly, after a certain distance, the beam and dot will be smaller with the expander than without, though at aperture you will have a fat beam.

killer pic cyp

 

[Alaskan]

Can't get anything for nothing in this world, it's true.... However the good news is I don't care about beam-width so much, I'm after maximum light at a distance over a smaller area so that works out for me. I bought about 2000 dollars worth of single mode R, G and B laser diodes (I can't believe I did that, but I did) to produce a net output of about 3.5 watts and want to build a rifle sized pointer and control the mixes, where it diverges in the distance, of course. Maybe there are some UFO's out there beggin for a light show? No, probably not so lucky to see one of those observing some strange human playing with light, but I'm hoping I can see a white spot as well as other colors on a mountain top with a telescope, if I can get the RGB modules close enough together so when the beams diverge into one another they will produce a white stream of light.

This is off topic for the section now, but can some of you suggest how I should drive these diodes without spending a fortune on laser diode driver circuit boards? I didn't buy them with driver boards, just the diodes inserted into Aixiz modules with wires on them. The diodes are the 120mW 3.8mm Red HL63603TG, 50mW 3.8mm Green PL520 and 120mW 3.8mm Blue PL450B diodes. Bought the RGB diode modules from DTR, I will be using my GB S1 lenses for them.

 

[The Lightning Stalker]

Assuming near perfect focus, the only way
to improve divergence is to start (and end)
with a wider beam.

Also, maybe not a good idea to aim lasers at
a UFO. I hear some of them have people
inside.

 

[Alaskan]

I thought the smaller the aperture surface of the diode the better? Perhaps we just can't build large single dyes or the expense is so high they are not common? Another piece of the puzzle.

As far as pointing lasers in the sky I wouldn't dare point them at anything, especially if it was a UFO which would more likely be an aircraft. I've lived near 60 years now and as a pilot myself with several thousand hours logged, have only seen them twice.

 

[The Lightning Stalker]

I don't think die size would make a
difference. Something about lenses just
causes a smaller input to have worse
divergence. I'm not sure, maybe it has
something to do with tiny imperfections
that are cancelled out when more lens
surface is used.

 

[Alaskan]

Do you agree that a good way to reduce divergence is instead of having the collimation lens right next to the diode, use one with a longer focal point away from the diode to allow it to expand further before collimation using much larger lens and thus wider beam?

Seems better to me because then you don't have the loss of hanging a beam expander in front of the initial collimation lens.

 

[Shakenawake]

probably. it kinda looks like thats what is going on in cyp's pic. always the more lenses the more power loss.

 

[Alaskan]

Now to figure out a way to do that with my little standard 12 mm modules. Ideas?

 

[Things]

The size of the active die area does determine the minimum spot size you can achieve, but in the case of our canned diodes it's usually quite tiny. You can focus an LED to a much narrower beam vs say, an incandescent globe for this reason.