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.
This paper studies the method of using a high-power fiber combiner to form a Gaussian beam into a flat-top beam, and divides the factors that affect the shaping effect of the flat-top beam. The theoretical analysis model of the fiber power combiner is established based on the waveguide theory, and the excitation characteristics of the fiber mode in the output fiber are analyzed. Based on the beam propagation method, the propagation and superposition characteristics of the highorder modes excited in the fiber combiner are simulated, and the flat-top beam synthesis method is studied. According to the simulation model, a high-power fiber combiner was made, and a high-power laser beam combining experiment was carried out. Finally, a flat-top beam with a beam quality of 10 and an output power of 20kW is obtained. During the experiment, we also found that the uniformity of the flat-top beam increases as the output power of the fiber laser increases.
A high power short-cavity random fiber laser employing the gain mechanism of the Yb-doped fiber and the half-open cavity structure and the temporal optical rogue waves (RWs) behavior are observed and investigated in the paper. The record output power without the stimulated Raman scattering (SRS) is promoted to 26.6 W in the YDRFL with the GDF length of 120 m. The stochastic pulses and temporal optical RWs are observed and demonstrated in the short cavity YDRFL for the first time. It is found that the proportion of RWs depends on the GDF length which can also affect the stability of output lasing. The research results reveal that achieving the relative stable output power requires the greater pump power for the shorter GDF length, although decreasing the GDF length will promote the maximum output power of the YDRFL without the SRS.
The random fiber laser (RFL) which is a milestone in laser physics and nonlinear optics, has attracted considerable attention recently. Most previous RFLs are based on distributed feedback of Rayleigh scattering amplified through stimulated Raman/Brillouin scattering effect in single mode fibers, which required long-distance (tens of kilometers) single mode fibers and high threshold up to watt-level due to the extremely small Rayleigh scattering coefficient of the fiber. We proposed and demonstrated a half-open cavity RFL based on a segment of a artificially controlled backscattering SMF(ACB-SMF) with a length of 210m, 310m or 390m. A fiber Bragg grating with the central wavelength of 1530nm and a segment of ACB-SMF forms the half-open cavity. The proposed RFL achieves the threshold of 25mW, 30mW and 30mW, respectively. Random lasing at the wavelength of 1530nm and the extinction ratio of 50dB is achieved when a segment of 5m EDF is pumped by a 980nm LD in the RFL. Another half-open cavity RFL based on a segment of a artificially controlled backscattering EDF(ACBS-EDF) is also demonstrated without an ACB-SMF. The 3m ACB-EDF is fabricated by using the femtosecond laser with pulse energy of 0.34mJ which introduces about 50 reflectors in the EDF. Random lasing at the wavelength of 1530nm is achieved with the output power of 7.5mW and the efficiency of 1.88%. Two novel RFLs with much short cavities have been achieved with low threshold and high efficiency.
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