10 bucks via PP to the individual who calculates this for me...

Hehe, i suppose it's right sometimes

My math agrees with Benm. Of course, this relies on the assumptions the aperture is exactly 3µm and you've got a perfect lens. Atmosphere increases scattering, but it does not increase divergence.

@Alaskan: That is above my level of expertise, sorry I didn't reply sooner. For some reason I was not checking my subscribed threads.

I built a beam expander for a PL520 single mode green diode and it sure does give a brighter spot at a great distance than my 1.4 watt NDG7475T laser diode, it's really cool how a low power 80mw single mode diode like this can not only compete with the much higher mutlimode diodes, but leave them in the dust how much more power you can spot at a distance with them.

Edit: I had to come back and report tonight we have a broken cloud layer at 22,000 feet and I was able to see a spot on the base of them using my little single mode laser diode. It was difficult to see, but when pointing at a hole in the clouds and back at a cloud I could clearly see a terminus spot appear each time, very weak due to the distance, but there.

Alaskan said:

I will ppal 10 bucks to someone who can calculate both the theoretical as well as give a good opinion on the likely divergence this diode will have when expanded to 100mm diameter using a PCX lens, any takers?

http://www.junktronix.com/ebay/proddocs/54xxdiodelaser_ds_cl_ae.pdf

Money to be paid upon confirmation the figures are good so please show me how you derived it. I will pay 15 dollars if you just want me to donate it to the forum instead.

Click to expand...

Use this app. https://lightmachinery.com/optical-design-center/lasers-and-laser-beams/gaussian-beam-propagation/
You have to use two optical lenses. I suggest one negative lens and of course one pcx lens.
Ignore the slow axis. Input the fast axis
Ignore the lower emitter dimension. Input the high divergence
Convert the emitter size to millimeters size = 0.0000003mm and input that into the appropriate box.

Thanks, I'm playing around with it now.

Alaskan said:

Thanks, I'm playing around with it now.

Click to expand...

You're welcome. In the results the numbers to watch.

Spacing of the first optic from the diode is important. I would predetermine how far from the diode this first optic will be placed, then actually measure the greater diameter, or you could just go for some arbitrarily low value, the lowest this app allows is 0.001 or -1000

I did some playing around with it. I assume the lowest beam diameter at the first lens -1000 diameter
I used a -6mm lens spaced 5mm from the diode and the second lens +100 pcx is spaced 97.19mm from the first.
Divergence of 30 degrees
The results are
Beam diameter at the second lens is 5.49mm
Rayleigh Range ( length) is 14,295.81mm this is an important number. This number tells you how much the beam will expand within that range which amounts to 1.4 times its original diameter

Alaskan said:

Thanks, and again for the explanation of why the rectangle output I'm observing changes by 90 degrees when viewed a distance away, I couldn't figure out why the beam did that before, now I see why, due to the divergence of that axis widening so fast.

Click to expand...

I'll jump in this old thread. (Was not monitoring for a long time :wave:

If you observe what you write, the beam is not collimated - it is focused :eg:
Why?

The emitter size 1 um x 3 um (not exact numbers matter, but the ratio). You add a lens and want to get the smallest spot at a certain distance. In optical terms you are creating an image of the object (the emitter). The spot size is proportion to a magnification of the optical system (M). For simple lens M is equal ratio between distances from the object to the lens (s1), and the lens to the image (s2) >> M=s2/s1. [ All these distances go into a formula 1/s + 1/s2 = 1/f ]
Thus having the large divergence on a fast axis but a smaller emitter, the dimension of a focused spot is smaller compared to a slow axis. (Just look at high power blue spots)

Back to the real life - lens' aberrations, a diffraction of the beam create more problems in calculations of the spot size. Collimation -> focusing to infinity -> good luck with a turbulence in atmosphere. Nevertheless it can be solved - like in shooting the Moon.