In order to reduce the nonlinear effects in optical fiber effectively and make energy output of the light beam much more uniformly, a flat-top beam-shaping device based on micro-structured optical fiber (MOF) has been designed in this paper. Output of flat-top fundamental mode is realized by introducing a low refractive index inner core in the refraction-guiding MOF. Based on this principle, output performance of flat-top MOF is simulated and alayzed with the Rsoft. The structure parameters of the flat-top MOF are obtained after optimization, and the diameter of the corresponding mode field is 10.37 μm and the defect degree is 0.16%. These results show that the flat-top fundamental mode with large mode area can be carried out in the designed MOF, and moreover, they also provide theoretical basis for the fabrication of the flat-top MOF.
Kilowatts class diode-pumped Cs vapor laser (DPCL) has been realized and this kind of lasers have military applications potentially for its high output power with high efficiency. Pumped by a fiber coupled laser diode, the key operating parameters of a DPCL are studied, including the spot size of focused pumping light, pressure ratio of buffer gases, vapor cell length, temperature of Cs vapor and reflectivity of output coupler. The spot size is properly chosen in the consideration of both the intensity scalability and mode matching. Pressure ratio is optimized under a modest pressure of mixed gases of helium and ethane. Under the optimized pressure ratio, the Cs vapor can absorb the pumping energy and convert it into laser energy efficiently. Besides, the temperature and reflectivity are also optimized to operate the DPCL in optimum state. The results have significant instructions for the experimental design of DPCL.
Diode-pumped alkali vapor lasers are famous in the field of laser for their significant advantages such as very high quantum efficiency (Cs 99.5%, Rb 98.1%, K 95.2%), good thermal management performance and excellent beam output quality etc. A rate equation model fully considering the spatial distributions of pumping light and oscillating light is established under the hypothesis of quasi-two-level energy system of DPALs in this paper. Meanwhile, expressions of threshold pumping power, mode-matching efficiency and output power and slop efficiency in low pumping and strong pumping, respectively, are obtained. Then, the influences of mode-matching efficiency on working performance of DPALs are discussed and analyzed. Results show that mode-matching efficiency mainly impacts on threshold pumping power, output power and slop efficiency in low pumping but that nearly has no effects in strong pumping. Therefore, this model benefits the further research of DPALs.
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