From: behzatsahin@gmail.com   
      
   On Tuesday, January 24, 2017 at 9:17:33 AM UTC+3, ewu...@gmail.com wrote:   
   > Light needs a surface to bounce off, otherwise   
   > light cannot be detected, for example when in a dark room, a light   
   > bulb or cfl is switched on then we can see the furniture, walls    
   > in that room because the light is bouncing/reflecting of those   
   objects/surfaces.   
   > When a laser pointer is pointed at a screen or at a target that spot can be   
   detected   
   > because the laser beam falls on the target and bounces back and then is   
   detected    
   > by a photosensor.   
   >    
   > But, what if it was possible to detect a spot or point of light in just air,   
   without   
   > the need of a surface for that spot/point to bounce of.   
   > What would be the practical applications of such an invention?   
      
   There are sideways looking power meters and beam profilers for high power   
   lasers, reflection from dust particles or in some cases O2 molecules are   
   enough. At high power levels air molecules will give all sorts of nonlinear   
   responses, and you can observe    
   many different wavelengths, raman lidar is a good example for that.  You'll   
   get no reflection in perfect vacuum though, in that case you need gravity   
   lenses and such sci-fi equipment:)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)