# Quantum Optics: 4-wave mixing

1. Jun 11, 2015

### marco1235

Hi all, I've some questions for you which challenge my brain a lot!

I'm dealing with a Photonic course and our professor introduced us a little bit of Non-Linear Optics. We spoke about Four-Wave-Mixing (4wm for brevity) and we said that when we shine a material with $\chi ^{3}$ with two frequencies $\omega_1$ and $\omega_2$ they mix to produce a downshifted (Stokes) wave at $\omega_3 = 2\omega_1 - \omega_2$ and an upshifted (anti-Stokes) wave at $\omega_4 = 2\omega_2 - \omega_1$. The frequencies have equal spacing, that is, $\omega_1 - \omega_3 = \omega_2 - \omega_1 = \omega_4 - \omega_2$. That's ok like in fig1 of the attached files. Now in our discussion in class the professor showed the second picture, where the process is a little bit different in my opinion (is this the well-known Degenerate Four-Wave-Mixing??). He sad that also this second process is a 4wm, and that we must think that $\omega_1$ and $\omega_2$ are now the same frequency $\omega_p$ of the pumping laser. But if they are identical I don't get $\omega_3$ and $\omega_3$ as from the formula above, because if $\omega_1 = \omega_2 = \omega_p$ then by substituting I get $\omega_3 = \omega_4 = \omega_p$. There's something wrong in my head of course!! XD

The last question is how is it possible with a degenerate-4wm to create a frequency comb!
I think that if I could undestand the first part, everything it would be (a little bit) more clear!
Thank you in advance and have a beautiful day!

Greetings from Italy!!

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2. Jun 16, 2015

### Staff: Admin

Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?

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