The story regarding how the United States first learned about the fundamental security vulnerability called “compromising emanations” is revealed for the first time in this 1972 paper called TEMPEST: A Signal Problem.
You can download it from the following link: https://packetstormsecurity.com/files/download/65944/tempest.pdf
Source: https://packetstormsecurity.com/files/65944/tempest.pdf.html