One of my microscopy application I would need a very narrow (0.5mm - 0.1mm) light beam (not laser!) to illuminate biological specimen. (cells) Is there any method to create such light beam? As an analogy, how would be possible to "compress" a 1cm in diameter collimated light beam from a powerful LED into a 0.5mm very bright light beam?
You can get such a beam to a certain extent. You need a very high luminance source.
Maybe you should look for etendue conservation to get an understanding.
Thank you very much for this answer. Etendue was new for me...
Actually, I am speculating about this:
https://www.edmundoptics.com.sg/f/compound-parabolic-concentrators-cpcs-3213/13944/
Actually you will select a portion of the phase space of the source and convert this one to a small diameter small angle beam. The possible outcome is independent from the actual optics.
For several practical reasons, I would not recommend a CPC (google CPC pictures and you will find 1000 sketches and 1 piece of hardware).
You could put together some specs of your beam and I'll suggest something to you for free.
Thank you for your answer.
Well, I would like to build a special illumination system for dark field microscopy. Now I use a classic darkfield condenser, what gives relatively good image quality. But I would like to try a different illumination method, when the light beam is perpendicular (or slightly oblique) to the axis of the objective. That is why I would need a very narrow but very high luminance. Previously I have already experimented using similar illumination, however not in darkfield setup and this oblique illumination gives a 3D like image of the cells what is very impressive. I would like to try this setup in darkfield configuration.
The idea came from the "legendary" Rife microscope where this oblique illumination was used. (By the way, what is the reason nobody has ever tried to replicate this ultra high resolution microscopy using highly advanced optics? Rife microscope: https://www.rife.de/the-smithsonian-report.html)
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