High energy (> 40 nJ), sub-100 fs, 950 nm laser for two-photon microscopy

Compact and high-energy femtosecond fiber lasers operating around 900-950 nm are desirable for multiphoton microscopy. Here, we demonstrate a >40 nJ, sub-100 fs, wavelengthtunable ultrafast laser system based on chirped pulse amplification (CPA) in thulium-doped fiber and second-harmonic generation (SHG) technology. Through effective control of the nonlinear effect in the CPA process, we have obtained 92-fs pulses at 1903 nm with an average power of 0.89W and a pulse energy of 81 nJ. By frequency doubling, 95-fs pulses at 954 nm with an average power of 0.46 W and a pulse energy of 42 nJ have been generated. In addition, our system can also achieve tunable wavelength from 932 nm to 962 nm (frequency doubled from 1863 nm to 1919 nm). A pulse width of similar to 100 fs and sufficient pulse energy are ensured over the entire tuning range. Finally, we applied the laser in a two-photon microscope and obtained superior imaging results. Due to a relatively low repetition rate (similar to 10 MHz), similar imaging quality can be achieved at significantly reduced average power compared with a commercial 80MHz laser system. At the same time, the lower average power is helpful in limiting the thermal load to the samples. It is believed that such a setup, with its well-balanced optical characteristics and compact footprint, provides an ideal source for two-photon microscopy. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

A compact and high-energy femtosecond fiber laser system based on CPA and SHG technology has been demonstrated, capable of generating high-energy, short-pulse laser with tunable wavelength. The system ensures pulse width of about 100 fs and sufficient pulse energy over the entire tuning range, performing well in a two-photon microscope.