From: pcdhSpamMeSenseless@electrooptical.net   
      
   On 2/1/2014 4:42 AM, haiticare2011@gmail.com wrote:   
   > I just got a book on evanescent waves, and it is focused on fiber   
   > optics, circuit lithography, and the like.   
   >   
   > But the question I wsnt to pose is, can the evanescent wave phenom be   
   > used in a humdrum manner to make simple optics measurements? Can even   
   > a cave man do it?   
      
   Sure thing.  Pick up a glass of water and look at your fingertips   
   through the free water surface.  At least some fingerprint readers do   
   the same thing.   
      
   > Here is experiment #1: Take an acrylic rod, and "pipe" light into it   
   > in a darkened room. When you touch it, light will "spill" out the rod   
   > around your finger.   
   >   
   > The first question is whether this is "evanescent." I think it is,   
   > but would like any opinions.   
      
   Partly, around the edges.  Most of it is just normal refraction.   
      
   >   
   > Next, I would like an explanation as to why light "spills" out. Part   
   > of this phenom is frustrated internal reflection, but the 'trigger'   
   > is evanescent, or is it? Could it be explained by just a refractive   
   > index change that interrupts TIR? Yes, I know the physics demo is   
   > done with separate light paths, to emphasize the E field evanescent   
   > nature, but is the evanescent phenom operative here also?   
   >   
   > Experiment #2: Years ago, I invented a light up sign that you see in   
   > restaurants everywhere. (1) (I invented it independently in 1975, and   
   > not sure if the invention was a lot of independent people - but   
   > that's not important.)   
   >   
   > OK - Here's the physics question about these signs. The magic thing   
   > about them is the letters "glow," you get net light output from the   
   > disturbance on the surface. How is that happening? And here is a   
   > thought experiment: If you were to mark on the surface of the sign   
   > with a transparent marker, like a piece of parraffin, would it glow?   
   > And more: If you were to mark with a white-board marker which leaves   
   > little or no bulk material, just some dye, would it also glow?   
   > Finally, it seems that roughing the surface also makes it glow. This   
   > probably trivial scattering untelated to "evanescent."   
      
   The guided light refracts normally into the binder of the marker ink,   
   then scatters off the particles and other irregularities.   
      
   >   
   > Finally finally - I'd be interested in hearing about attempts to use   
   > this effect in non-fiber optic regimes, for measurement purposes.   
   > Mark Johnson in his book describes light being piped into a falling   
   > stream of water inside a reflective cavity, but gives few details.   
      
   Attenuated TIR is used for spectroscopy of highly absorbing samples.   
      
   Due to the different attenuation rate in S and P polarized evanescent   
   light, TIR causes polarization shifts.  I've used that effect to adjust   
   the balance of interferometers based on polarizing cubes.   
      
   Evanescent coupling is used in pumping some lasers, because it helps   
   keep the pump light out of the laser output.   
      
      
   Cheers   
      
   Phil Hobbs   
      
      
      
   --   
   Dr Philip C D Hobbs   
   Principal Consultant   
   ElectroOptical Innovations LLC   
   Optics, Electro-optics, Photonics, Analog Electronics   
      
   160 North State Road #203   
   Briarcliff Manor NY 10510   
      
   hobbs at electrooptical dot net   
   http://electrooptical.net   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)