(Catching up and) Understanding 445nm diode lasers

[Tw15t3r]

So, it's been about 3 years since I was quite active on this forum, and I decided to come back since now I have slightly more experience with electronics than I did previously. I have been spending the last few days trying to see what's with the "new" (to me) 445nm diode lasers, and while I see everyone using ordered drivers or simple linear drivers, driving them to 2A and beyond for 3W and beyond, I can't seem to find any thread or post detailing what the 445nm diodes are typically like.

I remember there were threads talking about properties of red (650nm) and violet (405nm) diodes, e.g. they need 3.2v (iirc) to lase, and the PHRs needing 5v (?) or something, since most were trying their own DDL drivers or other more elaborate self-built drivers.

So what about these new M140s? What's the voltage needed to lase? And has anyone tried a DDL driver for it? What's the min voltage needed to run that?

Also, from back then, typical max current for running reds were ~320mA for 250mW (I think this was Jayrob's MXDL build), but that was pretty risky, with most people settling for ~250mA for just under 200mW of power. These were standard AixiZ acrylic lens (or for those who paid the premium Meredith Glass), and so I could tell what were typical current drive values. But now with a number of lens options available, I'm seeing a huge spread of powers, from 1.5W to 3W outputs.

So what is the typical drive current for the M140 for long life? And what's the max power that anyone has gotten so far?

I would like to get a feel for these new diodes, and I hope anyone's experience might be useful!

 

[pschlosser]

Welcome back.


3 Watts from a single 445 diode is rare. In fact, don't count on it. However, many (but not all) 445 diodes are capable of 2 Watts of output. The 445s are multimodal and nearly linear in their output, giving 1mW/1mA. With that said, 1.8A seams to be the accepted safe maximum to drive them.

The G1/G2 lenses produce more output, in part, because the opening is larger and more of the native fast and slow axis beam profile is seen as compared to acrylic lenses with a smaller (and beam profile improving) aperture. At these powers, the acrylic pens will not hold up.

 

[Bionic-Badger]

A little correction: the G1/G2 has the same size "opening" as other 6.3mm lenses but it has a shorter focal length (2.39mm). The short focal length does mean that the lens has a large numerical aperture (0.6 according to Laser66), i.e. a greater range of angles that it will capture light. More of the diode's output is captured by the lens when collimating, rather than reflecting/absorbing off the lens/lens barrel. The short focal length, in conjunction with using a single lens means the lens transmits more light than most other lens arrangements. The drawback of the G1/G2 lens is that the beam pattern doesn't look as nice as other lenses that chop off some of the laser's output (as Lazereer's long focal length lens does).

 

[Tw15t3r]

Hmm... aperture of 0.6? I take that would mean an F0.6 aperture (in terms of photography). That'd be very large indeed! And I'm guessing it also allows more light to be gathered from the diode, much like how widening the rear of the Aixiz module used to.

So, 1.8A is the typical current huh... And yeap, I've seen the chart for output power, 1mW on 1mA. Very nice! (almost looks like 100% efficiency until one realises that it's not being powered at 1V )

Anyone knows the voltage that these diodes need to lase? I saw on one thread something around 4V, but the person didn't seem sure.

 

[Bionic-Badger]

No, the f-number is roughly equivalent to 1/(2*NA) where NA is the numerical aperture. So it's more like 0.8333 in terms of f-number, which is still pretty good. Note that this is for a tiny 6.3mm lens, with a 2.39mm focal length, so you'd need a very tiny camera.

It's about 4-4.5V to lase. Most drivers are constant current and boost/buck, so it usually doesn't matter that much, as they'll adjust.

 

[Tw15t3r]

Ah ok, well, an F number like that is still large indeed! And yea, F-numbers are ratios, so I understand the "tiny camera" thing.

4-4.5V... righto! Although I'm planning to use a pre-made driver since PCBs are tiny compared to normal soldering, it's good to know what's it doing, so I'd have an idea if things go wrong, or if I wanted to customise further, etc.

Thanks for the help!