Hi All - I am trying to immerse myself in NLO and purchased Robert W. Boyd's Third Edition on Nonlinear Optics. I'm already struggling just 3 pages into the book.(adsbygoogle = window.adsbygoogle || []).push({});

We are looking at the polarization of a material in a NLO chromophore, so:

P(t)=[tex]\epsilon[/tex] [X(1)E(t)+X(2)E^{2}(t)+X(3)E^{3}(t)......]

where P is the polarization at time t, X is the NLO susceptibility for the corresponding ordered response, and E(t) is the strength of the applied electric field.

The text goes on to say "One might expect that the lowest-order correction term X(2)E^{2}(t) to be comparable to the linear response, X(1)E(t), when the amplitude of the applied field, E(t), is equal to the characteristic atomic electric field E(atomic)=e/4[tex]\pi[/tex][tex]\epsilon[/tex]_{0}a_{0}^{2}"

Then they derive a whole bunch of stuff, which I follow, but my question is why do we expect the second-order polarization to equal the first-order polarization when the applied field equals E(atomic)?

Why is that

if E(applied)=E(atomic) then

X(1)E(t)=X(2)E^{2}(t)

**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!

# Nonlinear Optics

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