High-power/energy all-fiber nanoseconds pulsed MOPA system based on Yb-doped spun tapered double-clad fiber

Nanosecond laser sources that simultaneously offer high pulse energy and narrow spectral bandwidth as well as an excellent temporal and spatial coherence are essential for coherence-sensitive applications such as holographic lithography. Achieving such performance in fiber-based systems is challenging because the amplification of spectrally narrow pulses is fundamentally limited by stimulated Brillouin scattering, which induces pulse distortions, backward-propagating light, and potential damage to optical components. In this study, we demonstrate a narrow-linewidth nanosecond fiber laser capable of generating 1.6 mJ pulse energy using an all-glass architecture based on spun, tapered, double-clad fibers, without the use of any active or passive Brillouin-suppression techniques. The laser produces 8 ns pulses at a repetition rate of 100 kHz, with a degree of polarization exceeding 97.5%. The output beam exhibits near-diffraction-limited quality (M2 ≈ 1.3) and a spectral linewidth of 53.8 MHz. At full performance, the system reaches an average output power of 160 W, corresponding to a slope efficiency of 76.6%. Measurements of the spatial coherence yield a value of 0.94. These results highlight the suitability of this compact fiber-laser platform for applications requiring high-energy pulses with excellent spectral purity, spatial coherence, and polarization stability.