研究目的
Investigating the limits of long-wavelength tuning of a holmium-doped fibre laser and achieving watt-level output at 2.2 μm.
研究成果
The study achieved the first watt-level (4.1 W) output from a silica fibre laser operating at 2.2 μm. Further optimisation of the resonator design should yield higher output power and higher efficiency in the 2.15-2.2 μm spectral region.
研究不足
The tuning range was limited on the short-wavelength side by increasing transmission for the dichroic mirror used for pump coupling, and at long wavelengths by the onset of parasitic lasing below 2100 nm. The slope efficiency of 50-60 % in the optimum operating region is lower by 10-20 % compared to experiments with the same fibre in linear cavities, which is likely caused by intra-cavity coupling losses.
1：Experimental Design and Method Selection:
A tuneable Ho fibre laser was built and optimised for high efficiency at long wavelengths. A 6.5 m long Ho-doped fibre with 35 dB core absorption at 1950 nm was used, and was resonantly free-space pumped by a 20 W 1958 nm Tm-doped fibre laser. The two ends of the gain fibre were bonded to AR-coated end caps to reduce parasitic lasing. An intra-cavity transmission grating was utilised to provide wavelength selective feedback with the first diffracted order fed into the other end of the fibre to form a tuneable ring cavity.
2：5 m long Ho-doped fibre with 35 dB core absorption at 1950 nm was used, and was resonantly free-space pumped by a 20 W 1958 nm Tm-doped fibre laser. The two ends of the gain fibre were bonded to AR-coated end caps to reduce parasitic lasing. An intra-cavity transmission grating was utilised to provide wavelength selective feedback with the first diffracted order fed into the other end of the fibre to form a tuneable ring cavity.
Sample Selection and Data Sources:
2. Sample Selection and Data Sources: The Ho-fibre had an all-glass triple-clad design for efficient 2 μm cladding pumping.
3：List of Experimental Equipment and Materials:
20 W 1958 nm Tm-doped fibre laser, AR-coated end caps, intra-cavity transmission grating, 20 % reflective mirror.
4：Experimental Procedures and Operational Workflow:
Output coupling was achieved with a 20 % reflective mirror in the free-space part of the ring, and unidirectional lasing with a contrast of ~50:1 was achieved by retroreflecting one of the outputs from this mirror.
5：Data Analysis Methods:
The slope efficiencies were measured from 2050-2200 nm. The power curve and optical spectrum at 2200 nm were recorded.
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