The emission band of holmium-doped silica fibers extends beyond 2200 nm, which means these lasers have potential of covering considerable parts of the atmospheric transmission window between ∼2100 nm and 2250 nm. However, efficient operation towards 2200 nm is challenging due to absorption in fused silica at the laser wavelength. Here we present a holmium-doped fiber laser specifically targeting long wavelength operation. The laser is implemented as a high-feedback wavelength selective ring cavity, and is tunable from 2025 nm to 2200 nm. A maximum slope efficiency of 58 % is obtained at 2050 nm, and a slope of 27 % at 2200 nm. A power of 5.5 W from a single aperture (8.9 W total) is demonstrated at 2200 nm. Our results represent extended coverage of the 2 µm spectral band with multiwatt-level silica fiber lasers.

We present a holmium-doped all-fiber master oscillator power amplifier (MOPA) system operating at 2108 nm targeting optical frequency conversion applications. The MOPA delivers pulses of 0.52 mJ energy at 10 kHz repetition rate after three amplification stages, with a close to square-shaped temporal profile of 50 ns duration, diffraction-limited beam quality and linear polarization. Challenges with achieving high gain and efficiency in the final amplification stage are discussed and attributed to quenching effects inferred from measurements of non-saturable absorption in the holmium fibers. Using this MOPA, we demonstrate a mid-IR conversion efficiency of 59% by direct pumping of a ZnGeP2 optical parametric oscillator.

We report an all-fiber Er/Yb master oscillator power amplifier at 1.55 μm, delivering 135 μJ pulses with 6 ns duration (full width at half-maximum) at 100 kHz pulse repetition frequency, limited by stimulated Brillouin scattering. The output contains <1% amplified spontaneous emission and has a beam quality of M=1.1. By seeding with a high-power distributed-feedback laser diode, only two fiber amplification stages are needed, which represents a low overall system complexity compared to reported sources of similar performance. With an optical-to-optical efficiency of 29% and a robust alignment-free design, the source is well suited for field applications in 3D imaging with a several-kilometer range, and we present results from using it in an in-house-developed scanning lidar system.

Nonlinear and optical limiting properties of carbon disulfide (CS 2 ) are characterized at 2.05 µm wavelength using a Q-switched Ho:YLF laser with high pulse energy. The nonlinear refractive index of CS 2 is measured using the z-scan technique, giving a value of (1.9±0.5)·10 −18 m 2 /W, i.e. (7.2±1.9)·10 −12 esu, for the 25 ns pulses from the Ho:YLF laser. Self-focusing and dielectric breakdown in CS 2 limited the output energy to 0.6 mJ in the optical limiting experiments for input energies of up to 150 mJ.