Coordination engineering enhances 920 nm emission in Nd3+-doped silica fiber for high-repetition-rate ultrashort pulses laser

Ultrashort pulses at 920 nm are highly desired light source in two-photon microscopy for the efficient excitation of green fluorescence protein. Although Nd3+-doped fibers have been utilized for the 920-nm ultrashort pulse generation, the competitive amplified spontaneous emission (ASE) at 1.06 mm remains a significant challenge in improving their performance. Here, we demonstrate a coordination engineering strategy to tailor the properties of Nd3+-doped silica fiber. With elevating the covalency between Nd3+ and bonded anions via sulfur incorporation, the gain performance at 920 nm is enhanced proactively and 1.06-mm ASE intensity is suppressed simultaneously. Using this fiber, the continuous-wave laser efficiencies and signal-to-noise ratio at 920 nm were significantly enhanced, especially, the laser efficiency reached up to 27.4%, twice that of commercial Nd3+-doped silica fiber. Importantly, the stable picosecond pulses at 920 nm were produced by passively mode-locking technique with a fundamental repetition rate up to 207 MHz, which, to the best of our knowledge, is the highest reported repetition rate of Nd3+-doped silica fibers. The presented strategy enriches the capacity of Nd3+-doped silica fiber in generating 920-nm ultrashort pulses for application in bio-photonics, and it also provides a promising way to tune the properties of rare-earth ions doped silica glasses and fibers towards ultrafast lasers.