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As I've few to no science background I may use the wrong terms/vocabulary.

As I try to create a tool for my job (wood worker), I try to create an unscalling with distance pattern from a laser DOE (1mW laser is enough, and I do have laser glasses for other tools).

An DOE (Diffractive Optical Element) pattern usually scale with distance as this

Using a set of lenses (in the reverse order of a camera) I should be able to get that

the lens is my image is definitely going to be more complicated.

My questions is:

As far as I could research using bad keywords, a "telecentric" lens should do, but why? Is there another way to achieve that? (with other objects than lasers)

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  • $\begingroup$ What is DOE? Please define acronyms that might be unfamiliar upon first use (here, in the title) And what is an unscalling pattern? $\endgroup$ – garyp Dec 26 '17 at 13:42
  • $\begingroup$ An unscalling pattern is a pattern that doesn't scale with distance (Im not a native speaker nor really good in English) $\endgroup$ – A.albin Dec 26 '17 at 13:52
  • $\begingroup$ en.wikipedia.org/wiki/Bessel_beam. See also axicon $\endgroup$ – mmesser314 Dec 26 '17 at 15:13
  • $\begingroup$ Why do you need a beam that does not diverge? Since you are a woodworker, I would guess you are using the laser to scorch the surface of the wood to draw a picture. Or burn away the surface to etch a picture into the wood. Except that a 1mW laser isn't powerful enough to do that. $\endgroup$ – mmesser314 Dec 26 '17 at 15:18
  • $\begingroup$ So DOE is Diffractive Optical Element? $\endgroup$ – garyp Dec 26 '17 at 18:33
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There does not exist any practical optical beam that does not eventually scale with distance. A Bessel-beam is a theoretical beam that would not scale, but in practice one can only make an approximate Bessel-beam (with, for instance, an axicon), but such an approximate Bessel-beam only remains in tack for a finite distance, then it also starts to diverge.

An example of a telecentric system is what is called a 4f system. It consists of two lenses placed one behind the other separated by a distance equal to the sum of their focal lengths. It is an imagining system: the pattern that exists in the transverse plane at one focal length before the first lens will be reproduced at one focal distance behind the second lens. That why it is calld a 4f system: the distance from the input plane to the output plane is 4 focal lengths. The size of the output pattern would be magnified compared to the input pattern by ratio of the focal lengths.

So if in your wood work application you need a particular sized pattern at a particular distance then you can use a 4f system. Otherwise, you may need to provide more information way you need a non-scaling beam in your application.

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