Convert normal white light to laser-like light? Is there a probable device that can convert white light to laser-like light without the need of an electrical stage in-between?
I'm thinking of something along this level.  A very precise filter and polarizer into a laser-tube of sorts where the waves would interact until they are strong enough to exit.
Is that right? 
I have a feeling I'm missing something important about how laser light works.
 A: Photons generated by a laser are coherent. In other words, they have the same wavelength (energy), and polarization and phase.
By filtering unwanted photons, you could create light with a narrow spectrum and the same polarization, However, you would have plenty of different phase contributions. Lasers work like copy machines for photons, based on stimulated emission, which is due to quantum mechanics. Therefore, this is nothing, you could replace with a non-quantum device.
The user The Photon is right, you could optically pump a laser medium, which then in turn would produce laser light.
A: An essential property of laser light is its coherence.
This property makes it extremely useful, almost indispensable, for producing holograms.
But when Dennis Gabor invented holography in 1947, lasers didn't exist yet!
He managed to squeeze some more-or-less coherent light out of ordinairy light from a mercury arc lamp by heavy filtering. Of course it was very far from perfect. Nevertheless, the first ever hologram was a fact.
Laser beams are often cleaned up with a so called spatial filter, basically a pinhole.
Such a device was also part of Gabor's "heavy filtering".
http://light.ece.illinois.edu/ECE460/PDF/Holography.pdf
