Katy Perry's sophomore album, "Teenage Dream," which spawned five Billboard Hot 100 No. 1 hits, pristinely captured the buoyancy of youth through gooey synth-pop. She's still championing optimism with super-producers Max Martin, Lukasz "Dr. Luke" Gottwald and Cirkut as her sonic guides, but the album is also a well-executed step toward adulthood. "Unconditionally" trades in the "Teenage Dream" idealism for a more reliable romance. Elsewhere, Perry evokes her recent divorce ("Ghost") with slowed-down guitar hooks.