High-power narrow-linewidth linearly-polarized Tm-doped fiber lasers operating at 2.0μm have attracted extensive interest in both scientific and industrial fields such as free space communication, remote laser sensing, coherent Doppler lidar wind detection, and gravitational wave detection. In this work, an output power of 160 W narrow-linewidth linearly polarized fiber laser operating at 2007.6 nm was realized by employing a homemade polarization-maintaining Thulium-doped fiber (PMTDF), corresponding to a slope efficiency of 45% and a 3 dB linewidth of 73 pm. The PMTDF was manufactured by modified chemical vapor deposition (MCVD) method combined with solution doping technology, with core and cladding sizes of 25 μm and 400 μm, respectively. The numerical aperture (NA) of the PMTDF is 0.1 and the cladding absorption is 4 dB/m at 793 nm. During the power scaling, the polarization extinction ratio (PER) maintained higher than 16.5 dB, indicating an excellent polarization maintaining performance of the manufactured fiber. The stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) effects were well-suppressed. This work could provide a good reference for the further power scaling of narrow-linewidth linearly polarized fiber lasers operating at 2.0 μm.
In this paper, the ytterbium-doped tapered fiber with core/inner cladding diameter varying from 31/250 μm to 62/500 μm was designed and prepared by the improved chemical vapor deposition and solution doping technology. An all-fiber nanosecond pulse amplifier was built based on the ytterbium-doped tapered fiber, and the influence of the longitudinal structure on the output characteristics of nanosecond pulsed laser was investigated. A nanosecond pulsed laser output with a central wavelength of 1064 nm, an average power of 832 W, a single pulse energy of 8.32 mJ and a peak power of 24.8 kW at a repetition rape of 100 kHz was achieved based on the ytterbium-doped tapered fiber with a large diameter uniform region length ratio of 62.5%. Compared with 50/400 μm uniform fiber, the ytterbium-doped tapered fiber showed obvious suppression effect on stimulated Raman scattering and beam degradation at a similar output power.
KEYWORDS: Oscillators, Fiber lasers, Cladding, High power lasers, Diodes, Ytterbium, Fabrication, Doping, Laser damage threshold, High power fiber lasers
In this work, deuterium loaded Yb-doped fiber has been proposed to mitigate mode instability in laser oscillator. Experimental results reveal that mode instability threshold power rises from ~459W to ~533W and ~622W at the condition of pristine fiber and fiber loaded with deuterium for 2 weeks and 4 weeks respectively. Mode instability threshold power is raised by more than 16% and 35% after 2 and 4 weeks deuterium loading compared to pristine fiber respectively, and laser slope efficiency is not affected by deuterium loading. The experimental results indicate that deuterium loading is effective in mode instability mitigation and showing potentials in further power scaling of high power fiber lasers.
The laser efficiency and temperature distribution in distributed side-coupled cladding-pumped (DSCCP) fiber lasers are investigated, using a precise and complete analytic model. We show that high-order mode pump handling and (N + 1) (N ≥ 2) DSCCP fibers can achieve a high laser efficiency when the fibers are separated. In terms of multistage pump schemes, a high laser efficiency requires an appropriate pump-node number and arrangement. According to our calculations, the temperature evolution along the signal fiber could give rise to a fluctuation in the case of strong coupling, which could decrease the mode instability threshold. The fluctuation period is usually determined by the DSCCP structure including the pump fiber number, the fiber diameter, and the fiber spacing. It is suggested that the mode instability threshold can be depressed through excellent DSCCP structure design and the selection on an appropriate pump scheme.
We have demonstrated a high power and high efficiency thulium-doped silica fiber laser using a cascade tandem pumping method. A 1915nm Tm-doped fiber laser was used as a pump source for another Tm-doped fiber laser with the output power of 63W at 1980nm, corresponding to the slope efficiency of ~80%, which is the highest power to our best knowledge. And the 3dB bandwidth was 0.24nm. The 1915nm Tm-doped fiber laser was pumped by 793nm diode laser and the slope efficiency was 51%. The preform of double cladding Tm-doped fiber for the tandem pumped fiber laser was manufactured by MCVD with using the vapor-solution hybrid doping method. The fiber has a ~25μm diameter, 0.098 NA(numerical aperture) core and 400μm diameter, 0.46 NA inner cladding. In the tandem pumped fiber laser, the resonant cavity consist of a high reflection FBG at 1980nm, flat fiber end and the homemade Tm-doped silica fiber. The optimal active fiber length was presented and it is found that when the length of homemade Tm-doped silica fiber was 7m, the efficiency was the highest. The influence of Tm concentration and ratio of Tm ion and Al ion on the efficiency was also explored. And it is found that the thulium-doped silica fiber with lower Tm concentration and higher Tm:Al ratio had lower optical efficiency. Meanwhile, the optimal fiber length became shorter.
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