High Power Passive Phase Locking of Four Yb-Doped Fiber Amplifiers by an All-Optical Feedback Loop

We report the passive phase locking of four high power Yb-doped fiber amplifiers with ring cavity.The interference patterns at different output power are observed and the Strehl ratios are measured.The maximum coherent output power of the fiber array is up to 1062 W by multi-stage amplification.The stable beam profiles of various phase relationships are observed by controlling the position of the feedback fiber,in good agreement with the calculated results.By using master oscillator power-amplifier(MOPA)architecture and broadband operation of passively phased systems,higher power scaling with high beam quality appears to be feasible.

The Improved Power of the Central Lobe in the Beam Combination and High Power Output

In order to increase the power fraction of the central lobe in the coherent beam combination of lasers in an array,the effects of the distance factor of near-field distribution on far-field interference patterns are calculated and demonstrated experimentally.An improved beam array of interwoven distribution is demonstrated to enable the power in the central lobe to reach 41%.An optimized mirror array is carefully designed to obtain a high duty ratio,which is up to 53.3% at a high power level.By using these optimized methods and designs,the passive phase locking of eight Yb-doped fiber amplifiers with ring cavities are obtained,and a pleasing interference pattern with 87% visibility is observed.The maximum coherent output power of the system is up to 1066 W.

Controllable Dual-Wavelength Fiber Laser

We demonstrate a controllable dual-wavelength fiber laser which contains a master laser and a slave laser.The master laser is a kind of ring cavity laser which can be injected into by the slave laser.The output laser wavelength is controlled by injected power of the slave laser;both single- and dual-wavelength operation can be achieved.Under free running,the master laser generates 1064 nm laser output.Here the slave laser is a 1072 nm fiber laser.The 1064nm and 1072 nm laser coexist in output spectrum for relatively low injected power.Dual-wavelength and power-ratio-tunable operation can be achieved.If the injected power of the slave laser is high enough,the 1064nm laser is extinguished automatically and there is only 1072nm laser output.

Compact All-Fiber 102W Picosecond MOPA Laser with a Narrow Spectral Linewidth

We report an all-fiber-based master oscillator power amplifier picosecond ytterbium-doped fiber laser with an average power of 102W and a spectral line width of 0.1 nm.The seed source is a compact single mode passively mode-locked fiber laser with an average power of 2.48 W.Finally,the laser maximum average output power of 102W picosecond pulses is realized by a direct all-fiber amplifier structure in one stage.The experiment enables the optical-to-optical conversion efficiency to reach 61.4%,with the central wavelength of 1063.7nm.A significant feature of this experiment is the spectral line width of 0.1 nm.The spectrum has no broadening or nonlinear effects when the pump is strengthened.

Competition of Stimulated Raman Scattering in H_(2)-CH_(4) Mixed Gases

Competition of stimulated Raman scattering was observed in hydrogen-methane mixed gases pumped by a KrF laser.The Stokespulse of methane gas oscillated,shortened and was destroyed with the addition ofvarious ratios of hydrogen gas.A model including the feedback of the cell windows as well as competition between hydrogen and methane gas agree well with the experimental observations.