We experimentally demonstrate the first polymer optical fiber Bragg gratings inscribed with only one Nd:YAG laser (266 nm) pulse. The gratings have been inscribed in a single-mode poly (methyl methacrylate) optical fiber, with a core doped with benzyl dimethyl ketal for photosensitivity enhancement. One laser pulse with a duration of 8 ns and energy of 72 µJ is adequate to introduce a refractive index change of 0.5 × 10-4 in the fiber core. The stability of the gratings has been confirmed and the strain and temperature sensitivity measurements demonstrate their tunable properties.