Femtosecond fiber delivery at 920 nm for two-photon microscopy

We present a femtosecond laser system at 920 nm delivering ultrashort pulses via a hollow-core photonic bandgap fiber (HC-PBGF). The laser system is designed to simplify two-photon microscopy applications and can be used for miniaturized two-photon microscopes.1 While previously presented solutions have been tailored to a specific length and dispersion coefficient of the HC-PBGF,1 we now show a compact and flexible scheme for dispersion compensation which is compatible with a wide range of fiber types and lengths. In addition, this new approach fully maintains the capability of software-controlled dispersion compensation in the range from 0 to -40,000 fs(2) after the pulse delivery fiber. Hence, the dispersion of common two-photon microscopes can be pre-compensated in order to obtain compressed pulses at the sample plane. Our newly developed system displays excellent long-term fiber coupling stability under varying environmental conditions. It is capable of polarization-preserving femtosecond pulse delivery at 920 nm and reaches Watt-level power after the delivery fiber, making it suitable for in-vivo brain imaging of GCaMP in mouse models.