From: dkcombs@panix.com   
      
   In article ,   
   Salmon Egg   wrote:   
   >In article ,   
   > "rll_sb"  wrote:   
   >   
   >> Perhaps I am misunderstanding your writing, but you begin by stating the   
   >> difference between specular and diffuse reflection -- this already precludes   
   >> absorption.  Reflecting materials whether specular or diffuse do just   
   >> that -- reflect.  Absorbing materials absorb the energy and re-radiate/emit.   
   >> They do not reflect -- either diffusely or specularly.   
   >>   
   >> With 30 years of experience in infrared, I believe the definitions of   
   >> reflection and absorption are pretty clear to me.   
   >   
   >Sorry Russ, but you do not have it quite right. A good analogy is that   
   >of an electrical transmission line with a load. In fact, it is that   
   >analogy, extended and slightly modified to handle plane waves that I   
   >have used for thin film calculations. Realize that index of refraction   
   >has the nature of an electrical admittance. Most transmission line   
   >equations are pretty much the same for admittance and impedance.   
   >   
   >Consider a transmission line with a characteristic index (admittance) of   
   >1. If you connect it to an infinite line of index 1, you get no   
   >reflection and the wave continues going down the line. If the index of   
   >long line is other than 1, you get a reflection at the junction. For   
   >index 1.1, you get a reflectivity of 0.23% out of phase and for 0.9 you   
   >get about 0.28% in phase.   
   >   
   >For a metal, the index is high. at n=100, reflectivity is 0.96% and out   
   >of phase. For germanium with an index of about 4, the reflectivity is   
   >36%.   
   >   
   >This discussion has not included lossy lines. Lossy media will have   
   >imaginary components to their characteristic indexes. As long as it is   
   >not 1, there will be a mismatch and a reflection. For example, if a   
   >transmission line is terminate with a large capacitor, there will be a   
   >large reflection. A strong absorber has a large imaginary component in   
   >its complex index even if its real part is exactly 1. That will give a   
   >large reflection.   
   >   
   >India ink also gives a strong dielectric reflection, But because light   
   >will penetrate several wavelength before being absorbed, its refractive   
   >index n does not have a large enough imaginary component to contribute   
   >to the reflection.   
   >   
   >I have previously talked about red and green inks. Get some and fill in   
   >a blot on smooth paper. Look at the specular reflection. At least try to   
   >see the effect. It is easy to see specular reflection of black print. It   
   >is readily available in magazines. Have you given that a try?   
   >   
   >Also look up pronzing in respect to color printing.   
   >   
   >--   
   >   
   >Sam   
   >   
   >Conservatives are against Darwinism but for natural selection.   
   >Liberals are for Darwinism but totally against any selection.   
      
   Nice post -- this and your prior one.   
      
   What do I understand and what do I not understand?   
      
   Well, I understand that you get reflection at an impedance   
   mismatch.  More than that, I could use some help.   
      
   What wikipedia (and other) sites would I look at to   
   improve my understanding of your posts here in this thread?   
      
   Thanks!   
      
   David   
      
   --- SoupGate-Win32 v1.05   
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