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Thanks, I think I saw the grating, it's the transparent thing right on the laser output, when unfocused the light has a series of lines. How far do you think the side beams are from the central beam on the focus point ?

I removed the laser diode from the DVD optic, and focused it using a microscope objective (with diaphragm, cause it's not a "plan" objective). Then I ve got enough focal length to take a picture of the spot, and upon zooming on the pic *ahem*, *cough*, I got a single spot. It would appear the...

-DVD lasers and cheap red laser pointers are 650 nm -one drive was Hewlett Packard rm465-h03 5 the other asus DRW-24B3ST -cant see the laser spot on a reflective surface (because it is reflected)

as proof of my sincerity please find a pic of my bench with the 2 dvd modules and the microscope objective circled in red: https://pasteboard.co/H7CZToY.jpg

if you dont look closely, i might seem to the naked eye that the beam is clean, but it really isnt if you look closely with magnification. And my target is 10 um, but what I see is more like 100 um (0.1mm) at best

for now I just tried with another dvd drive, I just rip the optics part, power it with my bench supply (after guess work for the diode pins) and then project it on a piece of paper. Same prob with the new (asus, 2nd hand, cant burn anymore) dvd I just tried. Can't take a proper picture...

i am trying to get a very small spot - for imaging purposes. I tried with and without pinhole ( the configuration I stated above are the optics i've used, but I dont use all of them at once, it's just the things i've tried)

i'm not sure anymore of why I use it. But originally it was for "spacial filtering", ie removing some artifacts from upstream optics.

no, one is a 5mW 650 nm red pointer that costs 2.5 usd the other is from Hewlett Packard rm465 DVD ROM drive

yes im in hanoi for focusing I used -nothing : the (used) DVD module already has a lens -microscope objective x10 achromat -home made pinhole (about 0.25 mm) They all give the same results, at least 2 lobes that can't be divided (by obstructing part of the light before the focusing optic)

Hello When I try focussing a regular cheap red laser or when I try with a DVD module, the minimum spot size I get is 0.1 mm (0.004") diameter. On top of that I get several dots in both cases. The several dots could be transverse modes from what I read. 1)I dont understand why I cant get a...