Supercontinuum (SC) generation in ytterbium-doped fiber amplifiers usually use single-wavelength laser seeds, which leads to the supercontinuum with strong Raman peak and unsatisfactory flatness. In this paper, a 1030 nm and 1064 nm dual-wavelength seeded ytterbium-doped fiber amplifier (YDFA) is demonstrated for the first time to generate a supercontinuum, the Raman peaks generated by 1030 nm and 1064 nm pulse lasers fill in the dips of each other, which is conducive to the flattening of the spectrum. The dual-wavelength seeded amplifier exhibits high spectral flatness with an 8 dB spectral bandwidth from 1 μm to 2 μm at the average output power of 1.92 W. The influence of the power ratio of 1030nm and 1064nm pulse laser seed and the impact of different inter-pulse time-delay of the two pulse lasers on the supercontinuum are investigated experimentally. The experimental results indicate that when the power ratio of 1030 nm and 1064 nm pulse lasers is 10:1, the flatness of supercontinuum has the best performance, which is determined by the absorption/radiation cross section of ytterbium ions, and the synchronous amplification of dual-wavelength pulsed seed lasers is more conductive to the broadening and flattening of the supercontinuum, as compared with the case of one seed laser. This work provides a new way to realize high flatness supercontinuum in YDFA.
Considering the difference in the divergence angle of different spectral components of supercontinuum laser, this paper researched the beam expansion effect of supercontinuum laser in atmospheric turbulence. The simulated laser transmission is carried out in the Von Karman model. The influence of turbulence of different intensities on the beam expansion is compared, the influence of turbulence on supercontinuum laser beam expansion with vertical, slant and horizontal transmission are also studied. The results show the beam expansion effect of strong turbulence on the short- wavelength part of supercontinuum laser is more obvious than that of moderate turbulence and weak turbulence. As the intensity of turbulence increases, the spot of the short-wavelength part increases rapidly first and then increases slowly and steadily, the spot of the long-wavelength part keeps almost unchanged at first, and also then increases slowly and steadily. The relationship between the elevation angle of laser beam emission and the beam width is calculated, and three cases are specifically analyzed. In the cases of vertical transmission and slant transmission, the beam width is related to the characteristics of the light source after collimation, which increases with the increase of the wavelength. When the laser is transmitted horizontally, the beam width has been greatly expanded, especially in the short-wavelength part. As the angle increases, the radius of the spot decreases rapidly first and then keeps almost unchanged. The radius of the spot of the short wavelength part reduces a larger proportion than that of the long-wavelength part.
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