In the world of scattering the angle at which you detect the scattered radiation is known as $q$, where

$$ \vec{q} = \frac{4\pi\eta}{\lambda}\sin(\theta/2) $$

I read in a lot of books that this is known as the scattering vector or "momentum transfer". What I am trying to understand is why it is called "momentum transfer"?

In the physical sense, say a beam of laser light hits a particle and creates dipole oscillations which re-radiate the scattered wave. What does the particular scattering vector have to do with the oscillations? Doesn't the particle just act as new source of light scattering uniformly in all directions? In this example ignore form-factor.

Thanks

In the world of scattering the angle at which you detect the scattered radiation is known as $q$, where

$$ \vec{q} = \frac{4\pi\eta}{\lambda}\sin(\theta/2) $$

I read in a lot of books that this is known as the scattering vector or "momentum transfer". What I am trying to understand is why it is called "momentum transfer"?

In the physical sense, say a beam of laser light hits a particle and creates dipole oscillations which re-radiate the scattered wave. What does the particular scattering vector have to do with the oscillations? Doesn't the particle just act as new source of light scattering uniformly in all directions? In this example ignore form-factor.