Using the modal dispersion equation with the phase-integral approaches, and con-sidering an eddy (or water mass) as a sound channel disturbance, the effects of the undisturbed channel, cold-core eddy and warm-core edd...Using the modal dispersion equation with the phase-integral approaches, and con-sidering an eddy (or water mass) as a sound channel disturbance, the effects of the undisturbed channel, cold-core eddy and warm-core eddy on the acoustic propagation characteristics are dis-cussed. According to the solutions of the dispersion equation, the relation between the modal Parameters (phase velocity, group velocity and interference distance) and the eddy intensity is obtained. When the plane wave (with an incident angle a) travels toward the center of a warm-core eddy (disturbed intensity BM ) 'double channel phenomenon' will take place in case of sin2 α < BM < 2(1 - cosα), and then the modal phase velocity and interference distance will have anomalous changes which are completely different from the case of the cold-core eddy.展开更多
The effect of transverse mode instability (TMI) is currently the main limitation for thefurther average-power scaling of fiber laser systems with diffraction-limited beamquality. In this work a main driving force for ...The effect of transverse mode instability (TMI) is currently the main limitation for thefurther average-power scaling of fiber laser systems with diffraction-limited beamquality. In this work a main driving force for TMI in fiber amplifiers is identified. Ourexperiments and simulations illustrate that the performance of fiber laser systems interms of their diffraction-limited output power can be significantly reduced whenthe pump or seed radiation exhibit intensity noise. This finding emphasizes the factthat the TMI threshold is not only determined by the active fiber but, rather, by thewhole system. In the experiment an artificially applied pump intensity-noise of 2.9%led to a reduction of the TMI threshold of 63%, whereas a similar seed intensitynoisedecreased it by just 13%. Thus, even though both noise sources have animpact on the TMI threshold, the pump intensity-noise can be considered as themain driver for TMI in saturated fiber amplifiers. Additionally, the work unveils thatthe physical origin of this behavior is linked to the noise transfer function insaturated fiber amplifiers. With the gained knowledge and the experimental andtheoretical results, it can be concluded that a suppression of pump-noise frequenciesbelow 20 kHz could strongly increase the TMI threshold in high-power fiber lasersystems.展开更多
文摘Using the modal dispersion equation with the phase-integral approaches, and con-sidering an eddy (or water mass) as a sound channel disturbance, the effects of the undisturbed channel, cold-core eddy and warm-core eddy on the acoustic propagation characteristics are dis-cussed. According to the solutions of the dispersion equation, the relation between the modal Parameters (phase velocity, group velocity and interference distance) and the eddy intensity is obtained. When the plane wave (with an incident angle a) travels toward the center of a warm-core eddy (disturbed intensity BM ) 'double channel phenomenon' will take place in case of sin2 α < BM < 2(1 - cosα), and then the modal phase velocity and interference distance will have anomalous changes which are completely different from the case of the cold-core eddy.
基金Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-416342637,416342891,GRK 2101(259607349)Fraunhofer Gesellschaft–Fraunhofer Cluster of Excellence“Advanced Photon Sources”.
文摘The effect of transverse mode instability (TMI) is currently the main limitation for thefurther average-power scaling of fiber laser systems with diffraction-limited beamquality. In this work a main driving force for TMI in fiber amplifiers is identified. Ourexperiments and simulations illustrate that the performance of fiber laser systems interms of their diffraction-limited output power can be significantly reduced whenthe pump or seed radiation exhibit intensity noise. This finding emphasizes the factthat the TMI threshold is not only determined by the active fiber but, rather, by thewhole system. In the experiment an artificially applied pump intensity-noise of 2.9%led to a reduction of the TMI threshold of 63%, whereas a similar seed intensitynoisedecreased it by just 13%. Thus, even though both noise sources have animpact on the TMI threshold, the pump intensity-noise can be considered as themain driver for TMI in saturated fiber amplifiers. Additionally, the work unveils thatthe physical origin of this behavior is linked to the noise transfer function insaturated fiber amplifiers. With the gained knowledge and the experimental andtheoretical results, it can be concluded that a suppression of pump-noise frequenciesbelow 20 kHz could strongly increase the TMI threshold in high-power fiber lasersystems.
