Is there any incoherent collimated monocromatic light source? I was looking for an incoherent monochromatic collimated light source. I know that if I shine a laser through some medium I'll partially lose the coherence but I will also sacrifice the collimation I was wondering if it exists an incoherent monochromatic collimated light source. Or any device to transform a collimated laser into an incoherent collimated light source. 

To my understanding, I can maintain the coherence even if the laser is not collimated, an incoherent collimated light source would be composed of photons with different phase shifts but collimated. Am I wrong?
 A: If light is monochromatic there is only one frequency $\omega$ (temporal coherence). If it is collimated there is only one direction of $\vec k$ (spatial coherence). Since $\omega = |\vec k| c$ this fixes the light to be a single plane wave and this is coherent in every sense.
A: LEDs emit incoherent light.
Now you are asking for a collimated light. This means, that the beams spread at a limited rate (angle) at certain distance.
Now if you accept LEDs as collimated (relatively), then it is just about monochrome.
Now LEDs are actually not monochromatic, but the spectrum is narrow relatively to human vision, so it is technically monochromatic.


A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A perfectly collimated light beam, with no divergence, would not disperse with distance. Such a beam cannot be created, due to diffraction.


https://en.wikipedia.org/wiki/Collimated_beam


The solid package of the LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner. For larger LED packages total internal reflection (TIR) lenses are often used to the same effect. However, when large quantities of light are needed many light sources are usually deployed, which are difficult to focus or collimate towards the same target.


https://en.wikipedia.org/wiki/Light-emitting_diode
So the answer is that if you want monochromatic light (and you accept that it has a narrow technical wavelength spectrum), and accept that the collimation is relative, then LEDs can work.
