Low power single mode vs high power multi mode laser diode divergence?

I've been googling for an hour trying to find specs on the LPC-836, the higher current version and can't. Do you happen to know if that one is multi-mode? I guess the LPC-826 must be single mode if the divergence is so good. I've been reading that a low mrad is also directly related to wavelength, the shorter the wavelength the better the mrad, so I'm also looking at some of the 405nm diodes now.

Laser Project said:

I've been googling for an hour trying to find specs on the LPC-836, the higher current version and can't. Do you happen to know if that one is multi-mode? I guess the LPC-826 must be single mode if the divergence is so good. I've been reading that a low mrad is also directly related to wavelength, the shorter the wavelength the better the mrad, so I'm also looking at some of the 405nm diodes now.

Click to expand...

I believe the 836 is single mode as well. I have one coming in the mail now so will confirm this when it arrives, from what I've seen posted though it's a very small improvement over the 826 in power.

I hear the bdr-209 blu ray diode has excellent divergence.

Reading about the 16X BDR-209 Blue Ray here: https://sites.google.com/site/dtrlpf/home/diodes/bdr-209-405nm-16x-diodes - If single mode, that is powerful. I researched the 836 last year and it puts out about 50mw more power than the 826, if I remember right. I just ordered one of the BDR-209's in a module from DTR for 105 bucks with a regulator board on it set for 600ma. If I like it, I might order a bunch of diodes from him and build from those.

Remember though, the 405nm wavelength is near ultra violet. It appears very dim to the human eye which threshold is generally considered around 400nm. (Everyone's eye is a different). I don't think you would be able to see the 16X BDR from miles away.

If it is just power density you need, and not visibility then blu-ray diodes win, but for a long distance visible beam you will get more bang for your buck with green. Also, low divergence may make for higher power density, but you will never be able to aim well enough to take advantage of that (getting 2 lasers pointed at the same target 100 miles away would be hard enough, let alone a dozen. My suggestion for signaling a human eye at the greatest distance for the lowest cost would be to get 100 overspec fleabay greenies and get them all wired up to a common power source that can provide at least a good 10 amps. Duck tape those suckers together or dissect and pop all the modules into a drilled aluminum billet and let 'er rip. And make sure you show us some pictures!

Good suggestion, I think you are giving me good advice, glad we agree but I feel a bit of whip lash after going the blue direction for so long on this to turn around and go to green now. If I could find a high power blue 445nm single mode I'd be after that.

OK, I will start searching the fleebay greenies, recommendations would be much appreciated if you or anyone has good experience with a particular module and seller.

I think I'm going try a Nichia NDB7875 with these:

Lasershow Parts - 4 x mag cylindrical lens pair

That should give the the brightest possible long distance dot with going multi diode.

Fifty bucks, for a single unit I don't mind spending a fair bit of change on optics, but if I'm going to duplicate this over and over into 25 or more units built in parallel, it adds up fast. I found some small expander lenses which might work with an Axis module, maybe... but don't have the specs, China man will sell them to me but can't tell me anything about them other than diameter.

Received the 700 mw 405nm single mode Axis module with internal regulator from DTR yesterday and as I was told it was, the beam is faint compared to 455nm. I don't need a bright stream, just wanted a bright spot but if you can't see the beam as strong, the spot won't be either.

Looked into buying a bunch of overspec Chinese units which state 80mw of power cheap (real 532nm power closer to 50mw with lots of IR output with it for 16.50 USD each) but when I add up the cost per mw, I might as well just use my 2 watt lab 532nm laser with a telescope to produce the results I want and maybe I'm wasting time and money to do otherwise but those units are heavy as well as bulky. I'd go after 520nm with expanders, once the price for those diodes come down closer to that of 455nm diodes of comparable power, but for now the price is still too high for me to buy 25 diodes.

My desire was to build a high power low divergence unit using multiple diodes at far less cost than I can possibly do otherwise and at 532nm, the cost isn't hugely different. I can do it at IR but then you can't see it I can do it with 455nm but then the divergence is hell unless using lots of beam expanders. If I can get those small 6mm diameter expander lenses to work inside an Axis unit, then I might have something, because of that it looks like I'm back to using 455nm 2 watt output diodes and expanders to reduce the divergence. Although, there is still the 660nm diode Rifter suggested, the single mode LPC-826, they can be had cheap and the divergence is reported to be good but I haven't found the spec sheet to confirm what the numbers are for that yet.