Instead of looking up the answer immediately:

What is FFT ? : A Short Intro to the Fast Fourier Transform - Keysight

The solutions work for Goodman's text is typically organized by chapter to reinforce foundational and applied principles:

The rigorous mathematical starting points.

You’ll likely be asked to find the intensity at the back focal plane of a lens.

Take the provided solution and re-derive it on a blank sheet without looking . If you cannot reproduce it, you haven’t learned it.

"Introduction to Fourier Optics" by Joseph W. Goodman is a classic textbook that provides a comprehensive introduction to the principles of Fourier optics. The solutions work provides a detailed and step-by-step approach to solving the problems presented in the book, and it is an essential resource for students and researchers working in the field of optics. The key concepts and takeaways from the book and its solutions work include the Fourier transform, diffraction, imaging, coherent illumination, and holography. Fourier optics has a wide range of applications in fields such as optical communication systems, imaging systems, spectroscopy, and holography.

He looked back at Goodman’s main text. There it was, in Section 4.3: “The angular spectrum approach.” The solution manual wasn’t giving him the answer; it was giving him the interpretation . It was whispering: “Stop calculating. Start transforming.”