During my experiments I want the emitted laser beams to come back with a different wavelength than the original wavelength using a fluorescent foil or fluorescent film.

The laser I'm currently using has a wavelength of 632.8 nm. The color of the emitted beams doesn't matter (it can have every color).

Therefore I want to ask if something like this is principally possible and if a fluorescent foil/ film does exist?

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    $\begingroup$ Depending on type of laser (pulsed/power etc you do not define this) you may be able to change wavelength by frequency doubling (or sum frequency mixing in general), use an optical parametric oscillator, make a super-continuum, or by exciting another laser. Fluorescence films will not work. $\endgroup$ – porphyrin Jul 4 '19 at 15:27
  • $\begingroup$ You have a He-Ne laser, so you need a fluorescent substance that emits at longer wavelength, which is a bit of a challenge since the nominal (but not actual) infrared starts at 700 nm. You would be far better of with a green laser pointer (532 nm) or even a 405 nm laser pointer (I have one, so I know they exist). These laser pointers are cheap and readily available. The nice thing about a green laser pointer is you can just shine it on things that you think might be suitable, e.g., red plastic wrap, and see if you get fluorescence. Good luck! $\endgroup$ – Ed V Jul 4 '19 at 22:20
  • $\begingroup$ @Ed V, The OP states that 'I want the emitted laser beam to come back' not just fluorescence, which makes the thing impossible with some arbitrary fluorescent material unless it is in a laser cavity etc. In any case HeNe's and laser pointers are very feeble, and as you point out will produce a little fluorescence, but no laser beam :) $\endgroup$ – porphyrin Jul 5 '19 at 9:08
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    $\begingroup$ @porphyrin Ah, I assumed the OP just wanted a little fluorescence, maybe to see where the He-Ne beam was going. We usually used unsolicited business cards or uranium glass for that. So your first comment pretty much says it all. Thanks for the catch! $\endgroup$ – Ed V Jul 5 '19 at 9:44
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    $\begingroup$ @Ed V, yes I've used cards the same way, often v good to detect uv light. $\endgroup$ – porphyrin Jul 5 '19 at 10:03

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