Cylindrical lens help

[ZeroPoint]

Hi guys,
I'm just now getting around to trying out Dave's cylindrical lenses for my P73 but I am either doing something completely wrong or I have been under a false impression as to what the cylindrical lenses actually do. I admit that I am not currently using Dave's 2mm lens for the diode (yet) but I was still expecting better results than I have been getting. Without the cylindrical lenses I get a sharp line with high divergence on one axis of the beam. When I add the cylindrical lenses the line becomes a rectangle with high divergence on both axes. I was under the impression that the purpose of the cylindrical lenses was to increase beam size with the tradeoff being lower divergence. Instead, it has simply increased the divergence of the slower axis to match the fast one so that I'm left with a high divergence rectangle instead of a high divergence line. Have I missed something? Any advice is much appreciated. Thanks in advance.

Luke

[dave]

You are doing something wrong I think.

The slow axis shouldnt change.. Do you have the stripe horizontal, or vertical like I suspect you do.

Start with the line horizontal. set the cylindriacal lenses ~25mm apart, and move them as a pair closer/further from the diode to get the best compromise between beam size at aperture and divergence

[ZeroPoint]

Hi Dave,
I have the line horizontal, although I did try it vertical as well but that was clearly wrong. I will try again with your advice although I think my real problem is my unstable work area. nothing is mounted firmly so the smallest touch or bump knocks everything out of alignment. I have only been doing coarse adjustments to see the general effects of the lenses but I suspect they are in need of very fine tuning to see the real benefits.

You said that the slow axis should not change so does that mean I should still expect to get a line for the end result instead of the rectangle I have been getting?

Thanks,
Luke

[m0f]

The line should shrink to a smaller line. Looking at the output without the lenses, with the line horizontal, the vertical size of the line (small already) doesn't change. The horizontal size which is long will shorten to almost a dot.

If the diode is rotated even slightly, you'll get almost a spiral type shape when adjusting the lenses, if this happens, adjust the rotation of the diode a small bit. Without the rotation exact, the end result dot will be bigger and not as clean looking as it can be.

And make sure to focus the collimator to infinity or just slightly less, until the line is as thin as you can get before starting. The alignment process is a bit of a pain, but with enough fiddling the results can be pretty good. The G71's are a bit better than the P73's for size of dot in the end, but can still get a reasonably small dot with the P73's.

And just to verify, you're using the smaller lens should be closest to the diode ?

[ZeroPoint]

Thanks m0f!! That actually clarifies another suspicion i had. The rectangle I was achieving wasn't actually a true rectangle but rather the edge of a spiral where the beam starts to wrap around to the other direction. It was really more of a diamond shape but it confirms just how particular these adjustments are and that, in addition to the position of my lenses, the rotational position of my diode is also off.

Yes, the smaller lens is the one closest to the diode with the concave side facing away. I'll fool around with it a little more as soon as I can pull myself away from this darn tv show -.-

Thanks for the help.
'

[buffo]

Start with the line horizontal.

Wait - just to be clear, you're talking about the beam profile in the FAR FIELD being a horizontal line, right? Because in the near field it should appear as a vertical line, and the image you'll see on the cylindrical lens face will also be a vertical line (albeit a very short one, only a few mm).

Adam

[ZeroPoint]

Yes, it is set up horizontal in the far field. The image on the first lens is a vertical line and the image on the second lens is a square. I'm still trying to get a decent far field image with the lenses in place but it does seem to be improving.

[polishedball]

The spiral look will also show if your not mounted or set perfect level with the lens.

[planters]

I use at least one adjustable cylinder in the pair and usually two to get the very smallest spots. Take a look at this video and this might help you to visualize the effect of each lens.

http://www.youtube.com/watch?v=A5sjyEGFOhE

[ZeroPoint]

Awesome video Planters! That helped a lot.