650nm 4W C mount

[planters]

PM to DTR after being asked to test these. He said to go ahead and post this, so...

OK,

To begin these are very good diodes. The divergence can be tamed with the use of independent cylinders for each axis. I was able to take the uncollimated beam out of the diode and collimate it to a 7mm by less than 2mm (the really impressive axis) and @ 11M focus it to a 12mm by 6mm spot. As a comparison in my projectors 2 Mitsu P73s can be fit into a 5mm apature scanner and at 11M give a 6mm x6mm spot. Forgive my smugness, but that's better than anyone else achieves....Anyway, when you analyze the beam dimensions; 2mmx7mm =14mmSQ vs 5mmx5mm =25mm SQ. Then, compare this to the farfield dimensions; 6mm x12mm =72mmSQ vs 6mm x6mm =36mmSQ, the result is that these are every bit as good/intense as 2 P73s except of course these C mount diodes are 2x as powerful as 2 P73s.

For line scanning applications(the company?) the good axis is extremely good and these would be a definite winner.

I did not try high power limits as you already have a handle on this. What I would like to try is multistage TEC cooling and temperature shifting down around the 630nm region. Along with this I suspect an impressive increase in power output.

With 6 of these I am pretty sure I could build a 30W red laser (world record?) that would fit the new EMS scanners...of boy. The problem is cost. @ $400 each I can take 4Mitsu P73s and combine them for the same output with less financial risk in the vulnerable components (a PBS does not go LED).

You OK if I post this?

Eric

[logsquared]

Funny, i was just sending a message to CDBEAM about these diodes 2 minutes ago.

Have you tried focusing the beam at a much greater distance? I found that I could focus the spot to a small diameter at around 10M but it would rapidly diverge after that. The beam would then be very large at say... 30M. This threw me off at first. After setting the beam to focus further away (30-40M) the divergence was much worse.

[planters]

That's surprising. I am sure the beam waist was not between the diode and the 11 M screen as I aligned it in fog. But, I'll check this tonight as the optics are still in place.

[logsquared]

In my case I think the beam waist was at the screen.

The nice square spot is pretty awesome, ehh?

[planters]

OK,I magnified everything and ran through a dozen cylinders. The results are pretty consistent @ 28 M (as long as I am able to accommodate inside for the position of the optical table). With a initial beam 4mm x 6mm V by H I get 6mm V (seriously) by 60mm horizontally. I continue to be amazed by the vertical at 3W it looks like a knife crossing the room. I think the FAC is a little off ( I mean a VERY little off) the line in the far field needs a little of a compromise in vertical focus. My guess the horizontal could be reduced with an aspheric cylinder. I'm saying this because the far field has the look of a focal plain that runs through a compromise focus. Anyone who has spent some time at a telescope eyepiece knows what I mean. It is hard to describe.

I am still plagued by cost. These are expensive and playing a hit or miss game trialing some aspheric cylinders isn't cheap and to do so for a diode that isn't going to be broadly used seems a little like a dead end. Don't get me wrong. These are pretty amazing and if cost competitive I think they could be lens-ed to blow away the Mitsu's

[logsquared]

Thanks for double checking.

I am trying to figure out where I went wrong in testing my sample? To get under 1mRad at full power I had about 25mm at aperture on the slow axis. Were your measurements taken at full ~4 watts? I noticed the raw divergence goes up really fast with increasing current.

I am starting to think they may be worth an extra look just because of the plain simplicity of the 1 diode approach.

Has any more info on their origin come up?

[planters]

Were you using a PCX lens? If so, then I got the same results you described when I first started this. You see a nice, neat... huge square which is actually the overlay of two poorly focused beams (and I now am beginning to think 4 beams and hence the temptation to try an aspheric) But it is clear that the two axises have different focal lengths. Often the asymmetry of the far field spot is called astigmatism. It is not. It is just asymmetry in the diode image. THIS is astigmatism. Once you see the vertical axis with essentially no divergence your going to get sucked in to this.

[logsquared]

Were you using a PCX lens?

Yeah PCX. I did try a 100mm fl cylinder on just the slow axis but the beam was way bigger than the 12mm wide lens at 100mm from the diode.

But it is clear that the two axises have different focal lengths.

Yes I definitely remember being able to focus both axis independently with a PCX. I don't think it made a huge difference in the divergence measurements, if I remember correctly.

Dang it planters, you are making me second guess my measurements

The reason I rejected the diode for use in my projector was the slow axis divergence was almost 2X that of the 71 and 73 and the emitter appeared to be 2x that of the 73.

Planters I trust your skill and diligence. I am wondering how I measured so far off? Unfortunately, I don't have the diode to retest. Is it possible the SA varies greatly from diode to diode?

The FAC corrected axis performed exactly like you describe.

[planters]

Yeah PCX. I did try a 100mm fl cylinder on just the slow axis but the beam was way bigger than the 12mm wide lens at 100mm from the diode.

That's defiantly not how the raw diode output expands for me. But, the performance is not typical. When I put a 100mm FL lens about 100mm from the diode the beam is about 9mm wide and the spot @ 28M is about 50mm wide. When I put a 50mm lens in about 50 mm from the diode, the beam is about 6mm wide and the far field is about 60mm wide. When I say "about" this not because I didn't measure very carefully. It is because the power output effects the divergence a little. The divergence is better than this @threshold and is maybe 15% worse @4W. This non-linearity for beam size and divergence is another reason that I suspect spherical aberration is present. The stronger lens introduces more spherical aberration and when oriented with the curved surface away from the diode it counteracts some of the aberration present in the raw output. The performance is significantly worse when I flip the lens.

[logsquared]

So, it looks as though the raw divergence is vastly different between diodes. At least I know I am not losing my mind.

Check this graph of the slow axis of the diode I tested.



If you do the trig. on 13.4deg at 100mm the beam width is 24mm.

This is what turned me off. If I had 9mm I would have been jumping for joy. These were to be used with the 9.5mm eye magics. I could have knifed 4 of them on the mirrors or 8 with pbs.

Maybe each diode could be tested by DTR? I would seriously consider using them if they would fit my scanners.