Optical and electrical bandwidth "outside" air

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MiddleVision
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My questions is about the conversion of a range of wavelengths in Hz, such as for an optical filter, in a medium different from air. Since the refractive index n is higher than 1, (let's say n=1.5) and than the value of c is almost 2x108 m/s, also the equation in the link below has to be corrected?

https://www.rp-photonics.com/bandwidth.html

When light is propagating in a different medium than air, is it also necessary to modify accordingly the equations for a Fabry-Perot etalon and similar filters?

Thanks a lot!
 

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MiddleVision said:
My questions is about the conversion of a range of wavelengths in Hz, such as for an optical filter, in a medium different from air. Since the refractive index n is higher than 1, (let's say n=1.5) and than the value of c is almost 2x108 m/s, also the equation in the link below has to be corrected?
If the propagation inside the medium is linear, there will be no modification to the spectrum of your laser.
MiddleVision said:
When light is propagating in a different medium than air, is it also necessary to modify accordingly the equations for a Fabry-Perot etalon and similar filters?
Yes, the Fabry-Perot equation must be modified to accommodate the dispersion of the medium.
 
MiddleVision said:
Does the filter effective index in the equation above have to be corrected then when that filter is not used in air?

https://en.wikipedia.org/wiki/Interference_filter
The fact that the index is called effective refractive index instead of refractive index only, most likely means that its value is determined by more than one media. But to be more accurate, I suggest that you check the related reference (ref. [2]) to know how that equation was derived.