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Forward and Backword representation of a plane wave

 
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abaset



Joined: 13 Feb 2009
Posts: 2
Location: Singapore

PostPosted: Sun Feb 15, 2009 8:13 am    Post subject: Forward and Backword representation of a plane wave Reply with quote

Hi all;
In a reflection and transmission problem of light off a dielectric slab or Fabry-Perot resonator, is it necessary to describe the wave in the slab as a sum of forward and backward wave or just a forward wave propagate in the relevant direction is enough. ?
knowing that in the above medium, the wave in the medium of incidence is Ei +Er with Er = rEi and the field medium of transmittance is Et = tEi

In this case, is there any difference between oblique and normal incidence.

any insight is very much appreciated
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hepcj
Site Admin


Joined: 23 Jun 2007
Posts: 125

PostPosted: Wed Feb 25, 2009 12:49 am    Post subject: Reply with quote

It would be one way but the reflected wave is determined by the parameters of the slab such as the thickness d of the slab, its refractive index and angle of incidence, theta. From this one can calculate the phase difference.

The phase between the forward and backward waves is given by

delta = (2pi/lambda) 2nd cos theta

where theta is the angle of incidence to the normal inside the material, (you can use Snell's law to calculate this angle), n is the refractive index of the slab.
If each surface of the slab has a reflectance R, then the transmitance is given by

T = [(1-R)^2]/[1+R^2 -2R*cos(delta)]

There will be a difference between normal and oblique incidence because the phase depends on the angle of incidence.
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