Both of my red lasers have the same thing. And it's not a lens artifact that can be cleaned, because I have repeatedly cleaned all my lens, and further, you can tell the lens artifacts (squiggly lines on the unfocused dot) from these.
I have a feeling it has something do with with it being open can....
It may also have something to do with not using an AR coated lens? Anyone know?
I just tested both my reds, one open can, one not, and the open can diode laser had a similar "dust effect" to the OP's. (May have been because the lens was dirty, I don't use my open can red that often.)
If cleaning the diode does not work, it may not be a dust problem.
" In the focus of a diffraction-limited beam (i.e., at the location where the beam radius reaches its minimum), the optical wavefronts are flat. Any scrambling of the wavefronts, e.g. due to optical components with poor quality, spherical aberrations of lenses, thermal effects in a gain medium, diffraction at apertures, or by parasitic reflections, can spoil the beam quality. For monochromatic beams, the beam quality could in principle be restored e.g. with a phase mask which exactly compensates the wavefront distortions, but this is usually difficult in practice, even in cases where the distortions are stationary. A more flexible approach is to use adaptive optics in combination with a wavefront sensor."
Ref: Encyclopedia of Laser Physics and Technology - beam quality, laser beam, M2 factor, ISO Standard 11146, divergence, nonlinear frequency conversion
Looks like a dirty or scratched lens to me personally. About the only way i've ever been able to get lenses clean is to remove them and completely submerge them in rubbing alcohol and swish them around. ***DON'T DO THIS WITH MULTI ELEMENT LENSES*** heh. It won't hurt them but they'll take forever to dry out unless you dismantle them.
Fremo: Do NOT polish the lens. Clean gently with non-lint Qtip or optical cloth using alcohol or a specialty fluid. Repeat at least twice. Personally, my 200mw O-like red laser has similar artifacts.
Lens in reasonable quality lasers are usually coated, any 'abrasive' will break down the coating since it is super-thin. Additionally, the lens may not be made of optical glass, but optical plastic (acrylic) which too is coated but is a softer material.
Wikipedia has a really nice writeup on 'Optical Coating' if you wish to read about it.
There probably should be a name for laser enthusiasts who seek artifacts in the beam... maybe 'laser anthropology'???
Um, you can get rubbing alcohol in pretty much any drugstore. turpentine is going to eat your coatings and/or lens if it's acrylic.. the AR coatings are delicate... so are the lenses. Never use paint thinner on anything you want to keep.