Install motion-sensing lights above the area containing the cat door. If raccoons come near your cat door at night, a sudden, bright light may act as a deterrent.
Place any pet food that is attracting the raccoons up on a counter or tabletop. While your cats can jump high and will still be able to access the food, raccoons cannot. Once the raccoons realize there is no food to be found in your home, they should stop coming around.
Lay a sheet of cardboard or a piece of thin plywood flat on the ground in front of the cat door at night. Sprinkle a generous amount of cayenne pepper over the cardboard or plywood; raccoons have a very strong sense of smell and dislike the odor of cayenne pepper, making it an effective natural repellent.
Keep your cats indoors at night if the raccoon problem is particularly bad and secure a lock on the cat door to keep raccoons out.