# Min spot size for light collimated from an optical fiber?

We are currently setting up an experiment in which we need to pipe laser light from one optical table to another. One way we were thinking of doing this was by coupling into an optical fiber, running it to the second table, and then recollimating the light using a lens. However, if we then wanted to focus that light down again onto a sample, would our spot size be limited by the core diameter of the fiber we used since it would be in effect acting as an extended point source? E.g. if we use a 100 micron fiber to source the light, would our spot size for focusing onto a sample also be limited to 100 microns?

• There's no reason in physics why this isn't possible in principle. In practice, getting good results will depend on having just the right lenses available. Mar 4, 2020 at 17:41
• To clarify, are you saying that 100 microns is the limit for our focused spot size (if we use a 100 micron fiber optic cable), and whether we can approach that limit depends on the quality of our lenses? Or are you saying that we should be able to focus smaller than 100 microns as long as we have good quality optics? Mar 4, 2020 at 17:59
• No, I mean you should be ale to de-magnify, but you'll need well-chosen optics to do it (particulary without aperture losses). If you were starting with 9 um fiber it would be more difficult to de-magnifiy (but still possible in principle). Mar 4, 2020 at 18:15
• Sorry again for not fully understanding. In your parlance, is 'de-magnify' equivalent to collimating the beam? Mar 4, 2020 at 18:24
• De-magnify means make an image that is smaller than the original object. Mar 4, 2020 at 18:27