I like to protect the diode window and the G2 is very efficient so I don't mind re expanding with a double concave then focusing from a wider point further away with a much wider lens, but how to calculate the lens needed so as not to have those wings, the sanwu 3X shows it can be done, now I just want to do it bigger.
I have used a single lens to work with the diodes natural divergence from a further/wider point and zoom that down to a point, if I get wings I can keep focusing until there's a center hot spot, but the wings look like wasted energy.
For true long range I think single axis correction of the aggressive axis is the 1st order of business, then we can work with a fairly consistent beam, also when one axis diverges so much more than the other this could lead to the wings/distortions when focusing over distance problem.
If we had a perfect round beam that had a divergence that was close to the same on both axis that would be easy, I have done this with the 532nm pumped crystal pair types very well, but the beam quality is very good.
The 3 element clips some of the ends and keeps the line shorter, so a bigger 3 element setup employed further out that also has more total magnification could be used, but just a single lens working with the natural divergence is going to run into the uneven divergence problem and make wings I would think, and I have seen, but there can be a best compromise setup, I just don't know how to calculate it.
One thought was to use the 3 element and sanwu 3X back half then use a much wider lens much further out, but the line width with that setup is already longer than using the G2 ( which makes the line really long ) and a cylindrical pair to reign in the aggressive axis, that method prior to the same 3X BE makes a big difference both in near and far field point of focus dot size.
I am glad to compromise so long as I get burning results, I feel like I should build my 2 diode unit with each NUBM44 using an efficient G2 primary ( that also protects the diode window ) and a 6X cyl pair to square up the beam some, combine via PBS then re expand that beam ( double concave ) ??? and focus it down with a 1. Aspheric, 2. Plano Convex/PCX, 3. Biconvex of a much wider diameter, the distance needed will be determined by the rate of re-expansion, but it will be re-expansion of a squared up beam.
But if I can cheat and get decent burning results with a couple of wider lenses that works for me, a tight line burns too, I use a burning line of light every day in my play.
Another thought is 2 corrected beams sitting side by side will diverge where they overlap more and more with distance, that in it's self will provide 12+ watts of fun.
Thanks for the links, I will experiment with those lenses and that search term is also helpful, I owe you a rep
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Biconvex lenses (BCX) and asymmetric lenses (ABL), similar to PCX ones, have positive focal lengths combined with convex surfaces. The surfaces of BCX lenses have equal and symmetrical radius of curvature, while ABL ones have both convex surfaces but with different radius of curvature. In the latter case there is a special relationship between the two surfaces, called form factor, which identifies the best shape that an asymmetric lens can have as a function of the distances between the lens and its conjugate points.
In cases where you have equal object and image distances, i.e. when an unitary magnification is required, BCX lenses are a viable solution that can completely cancel some aberrations such as distortion, lateral chromatic aberration and coma, while ensuring low residuals of spherical aberration. These types of lenses can be used as a magnifying lenses when the object is located, from the lens, at a distance less than the focal length and observed from the opposite side. For a BCX or an ABL lens with a focal length less than 250 mm, it can be also defined as the apparent magnification the ratio Ix = 1 / (4f), where f is the focal length expressed in meters. For lenses with focal length greater than 250 mm, instead, the previously expressed formula can be expressed as Ix = [1 / (4f)] +1.
I see why we use asymmetrical lenses with multi mode beams, we still get a diverging line that grows in width to height ratio, but it compensates some for the most visible MM projection, you have seen it, where it looks like a beam inside of a beam.
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I was about to buy this and noticed the angle of the glase through the hole in the left side, it looks slanted. The rear and front shape looks good but why that slant seen through the hole?
http://i.ebayimg.com/images/g/5fsAAOSwjqVZBoLH/s-l1600.jpg
