Tuned cascade laser

Tuning of a diode-cladding-pumped cascade Ho ³⁺-doped fluoride fiber laser is demonstrated using a single plane ruled diffraction grating. At the maximum available pump power, a tuning range 2955-3021 nm, an output power of >500 mW, and a bandwidth of < 1nm was achieved for tuning across the ⁵I ₆→ ⁵I ₇ transition. In a separate experiment, the ⁵I ₇→ ⁵I ₈ laser transition was tuned from 2064 to 2082 nm (with a bandwidth of < 0.5 nm) which simultaneously shortened the average emission wavelength of the free-running ⁵I ₆→ ⁵I ₇ laser transition of the cascade from 2.959 to 2.954 μm. This demonstration represents the first fiber laser that can tune beyond 3 μm.