Based on the simplified model of the tunable fiber laser system, the tuning performance of the laser was analyzed. Two kinds of tunable setups were established, which are the configurations with an external cavity and the configuration of the Littrow cavity. The tuning output characteristics experimentally were analyzed by means of setups. The simulation gives the output efficiency of two tunable lasers as 40% and 30%. In the experiment, the measured slope efficiency of the two lasers was 24% and 18.3%, and the tunable range of the two lasers was 32 nm and 40 nm, respectively. Both lasers could achieve laser output with good beam quality.
For spectral beam combining, an experimental system of dynamic beam quality caused by the thermal deformation of a grating has been designed and established. According to the theoretical model established, the distribution of the temperature field, as well as the thermal deformation of the grating, has been analyzed. Further, the combined beam quality and the intensity distribution have been numerically calculated in detail. The results show that the maximum temperature and the grating thermal deformation increase with the extension of irradiation time, resulting in side lobes appearing in the intensity distribution. In the experiment, the measured combined beam quality factor Mx2 was 1.29 without the thermal deformation. When the grating was heated by pump lasers at different times, Mx2 can arrive at 1.34, 1.37, and 1.41, respectively. The results reveal that the combined beam quality increases with the increase in irradiation time and changes rapidly at the beginning of heating, consistent with the theoretical analysis. The discussion and analysis of the dynamic beam quality are potentially valuable for reducing the influence of thermal deformation on the beam quality.
On the basis of the principle of spectral beam combining (SBC), a simple combining system using a reflecting volume Bragg grating as a combiner was designed in which two focusing lenses were used to control the incident angles of input beams, and two concave lenses were used to solve the problem of beam divergence caused by focusing lenses. The effects of the beam divergence angle (DA) on diffraction efficiency and beam quality were analyzed theoretically. The simulation results showed that a larger DA will reduce diffraction efficiency and lead to deterioration of beam quality. In the SBC experiment, the performances of the output beam with and without concave lenses were compared. The experimental results showed that, when the concave lenses were not inserted, the measured output power was 503 mW with a combining efficiency of 85.3% and the beam quality factor of 1.68. The experiment further showed that the combined power was 566 mW with a combining efficiency of 96% and a beam quality factor of 1.31 when concave lenses were used.
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