In the meantime, while I am waiting for the IR LED array to arrive I decided to give a try to an IR laser illuminator. I have some IR diodes harvested from old CDROMs so I wanted to try whether the laser illumination can work at all.
First question is whether the IR diode has strong enough output for area illumination. Upon information back to year 2004 I found, that the power output of these varies in between 40-60mW. I doubt that would be sufficient for my application but I wanted to test it.
The second question is whether the unfocused beam is wide enough to cover a certain area that is needed when flying with a race quadcopter. Another question is whether I can find any focusing lens that can be used to focus/unfocus the beam.
Third issue can be the beam pattern/shape, best would be to find an IR diode that has an oval or circular pattern.
After checking around 8-10 laser diodes I have I finally found one that seems to be fine for the job.
I have driven it by 90mA for the first round, but the beam was too weak. After some more reading I deciced to increase the current, to a higher amount.
It was a simple try/fail process as I did not know about the specs of the diode nothing at all.
So I settled at 260mA and to my surprise the diode is just slightly warm at its housing, but the optical power raised significally.
I have made two tests, one with a collimating lens and one without. Of course, the beam was wider without the lens, and there were also no artifacts on the picture.
The outdoor test made without the lens, just bare diode in original housing:
It is evident that the diode’s wavelength is not in the higher 900+nm range, rather around 780nm (the IR diodes used in CDROMs), as I can see the red glow. So for the stealth build I can not use it, but still, now it is clear that a laser IR diode application can be a working solution, even at lower output powers.
A big advantage of such a solution is small current consumption (<300mA) and small (tiny) size that is essential for mounting it on a quadcopter. Comparing to this, an IR led solution is much bigger, heavier and consumes more power.
I am ordering now some new 900+nm laser IR diodes for further testing. Stay tuned!