Getting Rid of Cat Spray Odor on Carpet?

HELP ME PLEASE. I just discovered that a neighborhood cat has been spraying in my cellar window onto my carpet. OMG, the smell is enough to gag you. What can I do to get the pee out of the carpet?

I have closed the window, so he won't be able to continue to do it. Any help you can give me I thank you for already.