Make air reflect light Is there any way in which air can be made to reflect light? By making air denser or by any other way? The task is to project images in air...
 A: If the wavelength of light is much smaller than the dimensions of obstacles; we don't encounter diffraction.$_1$ The wavelength of Visible light is $4\times10^{-7}$ to $8\times10^{-7}$ meters, which is greater than the radii of the most atoms, i.e around few $10^{-9}$meters.$_2$ So, you can expect diffraction and not reflection.  
Some of the molecules might have greater dimensions than the wavelength of light, but all the molecules won't reflect light, instead they might absorb. Even if some of the molecules do reflect, they appear so small, which will be difficult to detect from your naked eyes. Over all, the air in front of you appears transparent.  
Even if you make the air denser, it is important to have most of the molecules which reflect the visible light rather than absorbing. I would say it is possible but not impossible. Some times smoke is spread to make a laser beam visible in college laser experiments.

Credits: $_1$Karnataka 2nd PUC Physics textbook-2013 Edition-Page No.367 $_2$Modern's ABC of Physics Class XII-2013 Edition- Page No.789. Some modification has been done.
A: Air does reflect light.  That's how mirages come into being.  Granted, this reflection takes place at relatively low angles of incidence and at a relatively sharp boundary between air layers of different temperature (and thus density and thus index of refraction), but it certainly happens.
A: See this

This is taken from here
This is an article from 2011, but I believe the idea is not widespread.
It may not be called reflection on air, but it is as close as you can get! What is done is that high powered laser are pulsated to generate light points by making plasma excitation in atoms of oxygen and nitrogen in the air.
The name for this phenomenon is static volume volumetric display(See last paragraph in the wiki page)
