Do mirrors mess w/mrad?

[polishedball]

Been working on some p73s but haven't much a throw distance so I have to use 2 bounce mirrors to get to 50' but at every bounce the beam seems to get a bit larger than that entering. Anyhow at 50' the beam is about 30mm wide does this sound about right.

image.jpg

[logsquared]

cheap mirror can cause a "blooming" effect. 30mm seem about right for 50 feet. what is the size at aperture?

[badger1666]

If the mirror is not dead flat it can mess up the divergence

[Vidal Wolf]

higher powers can cause the overcoating on aluminum mirrors to melt & *bloom* making the beam divergence increase. Steve / Mixedgas informed me about that one.

[planters]

Been working on some p73s but haven't much a throw distance so I have to use 2 bounce mirrors to get to 50' but at every bounce the beam seems to get a bit larger than that entering. Anyhow at 50' the beam is about 30mm wide does this sound about right.

This depends completely on the near field beam size. With your 2mrad divergence You should be seeing about a 2.5mm square beam. If it is larger, then there can be improvement. When doing retro-reflective focusing (like in my video) even a standard quality 2nd surface household mirror works fine. The aberrations, aside from scatter and light loss due to non-scientific coatings, tend to be proportional to the size of the spot on the mirror and for approx 1 cm I have found these to be negligible.

[mixedgas]

No, not really. Its often a illusion to the eye, when the coating is poorly made and has a lot of scatter or a you have a plate glass mirror.

Steve

[nitelitedean]

I have seen and utilized a method to combat divergence off bounce mirrors, but it really only works with larger ones, 10 to 12 inch square. Normally the mirror is either held in place by clamps or glued in place with silicon. The clamped one is the best for this method. Remove the mirror and glue a 8-32 screw right in the center of it, on the back. Drill a hole in the rear plate for the screw to go thru. You will have to space the mirror off the back with an o-ring, you will have to source them, but they are not expensive. The o-ring should be about .250 thick and its diameter is just about the height and width of the mirror. Remount the mirror and use the clamps to make sure the mirror will not fall off. Put a wingnut on the glued bolt in the middle and tighten a very small amount. Assuming the mirror is .125 inch or smaller it will deform with a concave pattern and work against the divergence somewhat. It doesn't take much, since the distance is large. Put a little dab of silicon on the wingnut to hold it there. An adjustable concave mirror is what you now have....

Dean, Nitelite Lasers