New nanosecond Q-switched Nd:VO4 laser fifth harmonic for fast hydrogen-free fiber Bragg gratings fabrication

We demonstrate the fabrication of fiber Bragg gratings using a novel high-repetition rate nanosecond Q-switched Nd:VO₄ laser fifth harmonic (213 nm) source for the first time in boron and hydrogen-free, Ge doped fiber. Strong gratings are rapidly obtained with the phase mask technique in hydrogen-free B/Ge doped photosensitive fiber with relatively low average power (100 mW), as well as in standard Corning SMF28 fiber. The evolution of the refractive index change during UV-exposure is presented. Photosensitivity of fibers to the 213 nm light is compared to the fourth harmonic (266 nm) light, as well as picosecond 213 nm radiation and is shown to be significantly higher than both. We believe that the photosensitivity of SMF28 fiber is due to a single-photon rather than two-photon absorption process.