Raygun Gothic was a term coined in the short story, The Gernsback Continuum (pdf) . I encountered William Gibson’s story in the anthology, Steampunk II: Steampunk Reloaded (Highly recommended). Gibson uses the story to explore the dark side of the bright shiny future first envisioned in the early Science fiction pulp magazines introduced by Hugo Gernsback.
Cohen introduced us and explained that Dialta [a noted pop-art historian] was the prime mover behind the latest Barris-Watford project, an illustrated history of what she called “American Streamlined Modern.” Cohen called it “raygun Gothic.” Their working title was The Airstream Futuropolis: The Tomorrow That Never Was.
— William Gibson, The Gernsback Continuum
This future society was depicted as the triumph of technology in the service of mankind. This fictional world, like most of the pulp fiction of the time was full of the biases that filled American Media. The future would be an idealized American society that contained only a white-anglo culture. Robots and aliens would replace other races and ethnicities.
In Gibson’s story a photographer is hired to gather images of the architectural remnants that were based on this vision of the future. As he explores the American country-side taking photographs, he becomes aware that reality is shifting. He is somehow entering this alternate America. Is he having a mental breakdown ? Is he tuning into parallel time line ? Or is reality bending to accommodate his photographic vision ?
Note: While double checking background information, I discovered a short British film, Tomorrow Calling, an adaptation of The Gernsback Continuum. It is an an interesting & effective adaptation, but I suggest that you read the story first ( see link above).