Abstract
In an actively Q-switched fiber laser (AQS-FL) a type of acousto-optic modulator (AOM) or (potentially) electro-optic modulator (EOM) controls the generation of output nanosecond wide pulses. An integrated Gaussian pulse shape is desirable in many applications such as material processing, microfabrication, ultrasound generation, gold photothermal therapy, etc. However, because of the system dynamics, generation of perfect Gaussian pulse shapes is not guaranteed in an AQS-FL, additionally designing the AQS-FL for a desired pulse peak and duration is an inverse problem which needs cumbersome trial-error efforts. We have developed a framework consisting of a rigorous FDM method plus a dedicated and innovative multi-objective genetic algorithm (GA) which assists the designer in achieving the desired Gaussian pulses within a reasonable time frame. The developed GA evolves the timing parameters of modulator plus the pump power and fiber length until the suitable goal is reached. To demonstrate the flexibility and design feasibility of our GA, three different single pulse and pulse train generation scenarios on a 7.5 m long Ytterbium-doped double clad fiber (YD-DCF) are examined to achieve the Gaussian,150 Wand 200 W peak power, 250 ns and 300 ns width pulses. To the best of our knowledge, it is the first implementation of an intelligent algorithm for optimizing the output pulse of an AQS-FL. It is worth noting that depending on the fiber host material and modulator specifications, much higher peak powers and different pulse durations are feasible, furthermore in case of utilizing the AOM, the pertaining limitations and feasibility are considered.
Highlights
A Gaussian pulse shape is defined by its peak power and full-width at half-maximum (FWHM) parameters, it causes an appropriate thermal profile in materials, as such the Gaussian profile pulses are desirable in different applications such as material processing, microfabrication, marking, medical equipment, LIDAR, etc
In summary, we have developed a dedicated finite deference method model based on the distributed traveling wave model for actively Q-switched fiber lasers (AQS-FLs)
We have developed a dedicated genetic algorithm (GA) from scratch to optimize the output pulse and repetition characteristics of the AQS-FL
Summary
Gaussian pulse shape is defined by its peak power and full-width at half-maximum (FWHM) parameters, it causes an appropriate thermal profile in materials, as such the Gaussian profile pulses are desirable in different applications such as material processing, microfabrication, marking, medical equipment, LIDAR, etc. Study of RO effect on the AQS output pulse shape would be possible through switching on the pump power just in the time of modulator ramp up under different rise time (tr ) conditions. In order to achieve a valid result, the simultaneous effect of different ASE channels (competition of spectral components) should be calculated at every specific time and position step This process is accomplished via solving a number (K ) of the above PDE sets simultaneously or through a self-consistent iteration loop; otherwise the results would not be trustable. All of these parameters except the pump power are unitless.
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