High-energy, low-repetition broadband ultrafast lasers empowered by hollow-core fiber

Low-repetition-rate ultrafast lasers with high peak power and broadband spectrum are key components in applications such as industrial processing, lidar, optical imaging, and spectroscopy. To turn these capabilities from concepts into reality, the missing element is a low nonlinearity and low dispersion waveguide with purified transverse mode that can be mass-produced. Here, a self-made anti-resonant hollow-core fiber with a nonlinear coefficient as low as 1.97×10-7 and single transverse mode low-loss transmission is inserted into a nonlinear polarization rotation mode locking cavity with simple and compact configuration to realize high performance ultrafast laser. A turn-key single-pulse mode-locked all-fiber laser with repetition rate as low as 2.63 MHz, peak power up to 103 kW, and bandwidth of 35 nm is demonstrated. The stable phase relationship of the different wavelengths enables highly coherent swept signal with low frequency noise of 97 Hz2/Hz by time stretching technology, which has been demonstrated for coherent detection systems. A 1.6 m detection range with a MHz-level refresh frame rate in swept source optical coherence tomography system is demonstrated. Besides, a fast vibration signal of 113.2 kHz is reconstructed by demodulating the phase of the interference signal. Furthermore, the laser is also used in a dispersive Fourier transform spectrometer to achieve fast spectral monitoring with the highest resolution of 1.54 pm. The proposed scheme provides a new perspective for developing high-performance low-repetition-rate mode-locked lasers and promoting the development of optical applications.