This might be a bit to specalised for some of you, but i am trying to calculate the number of modes that light can propegate in a material. The question is as follows(adsbygoogle = window.adsbygoogle || []).push({});

Consider a cavity that is a cube with the side length a = 1mm filled with water (refractive index(n) 1.33). Calculate the number of cavity modes that fall withing a bandwidth Delta f = 1MHz at the frequency of Ar laser (vaccume wavelength 488nm)

Now, we have been taught the equation that the numer of modes N in the material, N = (8Pi * n^3 * a^3 8f^3) / 3 c^3 where c is the speed of light in vaccume.

We have also been taught that The number of modes in a frequency interval between f and delta f is given by DeltaNf = (dNf/df)Deltaf

I get an answer of 827 modes in that interval. I got the frequency by using f=c/landa in the vaccume and remembered that the frequency of light is the same in every medium. (6.1475x10^14 Hz) Is this the right frequency to use in the water? And am I calculating the number of modes right?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Number of modes in a cavity

Can you offer guidance or do you also need help?

Draft saved
Draft deleted

**Physics Forums | Science Articles, Homework Help, Discussion**