content_image/319676.jpg content_image/319677.jpg content_image/319678.jpg content_image/319679.jpg content_image/319680.jpg content_image/319681.jpg
of the integration over all space. Therefore we have that 

<img src='content_image/319676.jpg'>

<img src='content_image/319677.jpg'>

Note that we have implicitly taken k 0 = | ⃗ k | and will continue to do so for the rest of the calculation. 

If we define 

and recall that 

<img src='content_image/319678.jpg'>

<img src='content_image/319679.jpg'>

<img src='content_image/319680.jpg'>

<img src='content_image/319681.jpg'>

