Wings like this ---O--- on open can red diode beam

[kecked]

Has anybody had an issue with open can reds having "wings" on the beam? I am seeing a nice round dot with straight lines coming from the center like this ---O--- Never saw this before. It is not the lens as i tried several different ones. I'm going to try blackening the inside of the colimator next to reduce and possible reflections. Strange thou since I have never needed to do this before.

[andy_con]

sure do, dont know the reason but its a normal red thing

[kecked]

Any suggestions to cure it?

[andy_con]

why is it a problem?

[kecked]

yes, anytime the beam stops on a hot spot it shows the line.

[ElektroFreak]

That's also present on the 445nm diodes, except its a full rectangular halo. The wings/halo are caused by light leakage around the edges of the diode die and they can be found on most higher-powered diodes.. the only way I can think of to eliminate them completely would be to use a spatial filter.

[kecked]

What is a spatial filter and were do I find one?

[drlava]

if you put an aperture mask on the back of your collimating lens it should help with this. Look up the back focal length of the lens and find the diode raw divergence and that with a little trig will tell you the size of the mask necessary.

[allthatwhichis]

Just throw a mask up right before the scanners... assuming you are pointing them at scanners.

[ElektroFreak]

What is a spatial filter and were do I find one?

A spatial filter basically a pinhole of a very tiny size. The hole that the laser beam passes through should be circular and as close as possible to the smallest possible spot size at the focal point of a focused perfect laser beam (TEM00, m^2 of 1) at a given wavelength, so very tiny. The laser beam is then focused to a point and the filter's pinhole placed precisely at the focal point. Ideally The resulting output should be TEM00 with very nearly gaussian power distribution, but there may be some power loss..

Realistically, a spatial filter would be a pretty advanced way of getting rid of the wings, but it is the only way I know of to get rid of them completely. Both suggestions above will help with the issue, but there will still always be a little bit of the wings visible, particularly in the far field. Depending on the distace from aperture to your first scanner mirror, allthat's idea above would probably give the best results. The farther the beam travels from the aperture before the mask, the better.