Source: http://aoot.osa.org/oe/abstract.cfm?uri=oe-27-6-8738
Timestamp: 2019-04-26 11:41:50+00:00

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A high-power multi-transverse modes random fiber laser (RFL) is investigated by combining a master oscillator power-amplifier (MOPA) configuration with a segment of extra-large mode area step-index multimode fiber (MMF). Spatial coherence of the high-power multi-transverse modes RFL has been analyzed, which shows that speckle contrast is reduced dramatically with the output power increasing. In this way, considerably low speckle contrast of ~0.01 is achieved under high laser power of ~56 W, which are the records for multi-transverse modes RFLs in both spatial coherence and output power. This work paves a way to develop high-power RFLs with very low spatial coherence for wide-range speckle-free imaging and free-space communication applications.
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Fig. 1 Schematic diagram of experimental setup. HR-FBG, high-reflectivity fiber Bragg grating. LD, laser diode. YDF, Ytterbium-doped fiber. CPS, cladding power stripper. ISO, isolator. MMF, multimode fiber. RFL, random fiber laser. PA, power amplifier.
Fig. 2 (a) Optical spectra of the random-lasing seed light measured at different pump power. (b) Output power of random-lasing seed light versus pump power.
Fig. 3 (a) Optical spectra of the amplified RFL. (b) Output power of the incorporated pump power in the power amplifier. inset, photograph of the output power value after the amplified light is exported from the MMF.
Fig. 4 Speckle patterns formed after light passing through a ground glass diffuser at different power.
Fig. 5 Speckle contrast with variation range verse output power of RFL.

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