Go to Adobe's main web page and search for FFT or Fast Fourier Transform. You should find what you want.
That's not an adobe plugin if your talking about a Fast Fourier Transform filter, it's a third party plugin/filter that your not likely to find on the adobe site unless someone has linked to an FFT download in a forum post.
What operating system and version of photoshop are you using?
If your using windows, then here is one of the more popular FFT plugins for photoshop: