# I Extinction index

1. Apr 7, 2016

### Carmen_8

We have a monochromatic plane wave with a frequency ω=10^15 (1/s). It is spread in a medium whose resonance frecuency is also ω=10^15 (1/s). The wave is attenuated in the spreading direction. In 1 cm, the electric field of the wave is 10 times smaller. Give an expression for the extinction index (K) (imaginary part of refractive index).

I know the expression for K(ω) in the special case that the wave's frequency is equal to the medium's resonance frequency. The problem is that I don't know what to do with the other data: 'In 1cm, the electric field of the wave is 10 times smaller'.

2. Apr 7, 2016

### nasu

What is the meaning of the extinction index? What equation do you know that describes how the amplitude of the wave decreases with distance from source?

3. Apr 7, 2016

### Carmen_8

The extinction index is the imaginary part of refraction index. The physical meaning has to do with the amount of attenuation of the wave. And teh answer for the second question..the only one that I have in mind is the expresion for electric field as a monochromatic plane wave with a complex wave vector.

4. Apr 7, 2016

### nasu

OK, and which part of the equation of the plane wave with complex wave-vector describes the attenuation of the wave?
It will be more useful to write the actual equation rather than describing it in words.