Lenses and in between

[ez2022]

Hello to all ,
well i got my first laser pointer , damn topic is so interesting .
I'm trying to learn a bit about lenses .
so i have couple of question that are not new i guess , sorry for the fishness .
i could not find any resources for this info .

is focal length will represent the distance from LD to lens in mm ?
do i need a collimation lens before beam expender , if so .... what is the right distance to lens ? ( i read that you can use focus or collimation lens )
can i use any collimation lens with beam expender ?

 

[Borislav@87]

I don't know what you expect anyone to tell you. Give information about the laser. You can upload a picture of the laser, how it was made and what lens it is currently with. Not all lasers can be replaced.

 

[RA_pierce]

1. is focal length will represent the distance from LD to lens in mm ?
2. do i need a collimation lens before beam expender , if so .... what is the right distance to lens ? ( i read that you can use focus or collimation lens )
3. can i use any collimation lens with beam expender ?

1. Almost. The "back focal length" is more useful for plano-convex aspheric collimators and plano-convex spherical lenses. It represents the distance between the lens surface closest to the virtual focal point of the lens (where the diode emitter should theoretically be positioned).
2. Yes. A beam expander works by expanding an already collimated beam. There is an inverse relationship between minimum beam divergence and beam diameter. Beam expanders work by increasing beam diameter initially in order to reduce divergence angle.
3. Theoretically, yes.

Take a look around at Edmund Optics learning resources. They offer some good information on optics that might help build your basic understanding of how laser collimation works.

Welcome to the forum.