高功率掺鐿光纖雷射之研究

Abstract

摻鐿光纖雷射近來以每年功率倍增之趨勢成長，相較於傳統高功率雷射，其在千瓦級以上功率輸出時仍可保持60%光轉換效率與接近繞射極限之光束品質；其他如激發光源為半導體雷射故使用壽命長，增益介質為光纖形態故可輕薄短小且散熱性能佳，以商業角度來說可大幅降低營運維修成本，大有取代傳統高功率雷射在雷射加工、非線性光學與雷射電漿物理上的運用。在雷射性能上，連續輸出、Q開關奈秒級脈衝或鎖模飛秒級脈衝之光纖雷射及其光纖功率放大器之技術發展已逐漸成熟。未來的挑戰為單模十千瓦級與單頻線極化之連續輸出以及百毫焦耳級脈衝能量與千瓦級平均功率之脈衝輸出。 在本論文中，作為初步的研究，我們成功地以入射功率20 W、波長915 nm光纖耦合半導體雷射來端面激發摻鐿光纖，成功產生波長1064 nm且連續功率9 W之雷射，並與模擬結果在雷射斜率效率、激發閥值與中心波長上得到良好驗證，並分析其端面耦光效率之最佳化、摻鐿光纖吸收量測。

Recently, with the rapid growth of Yb-fiber laser powers, the great advantages of Yb-fiber lasers over the conventional high-power lasers are the possibility of achieving extremely high conversion efficiency of 60% at kW outputs, and yet maintaining high beam quality close to the diffraction limit. The particular features of Yb-fiber lasers, including with laser diode as the excitation (i.e. longer lifetime, low cost) and with fiber form as the gain medium (i.e. compact) , is of major significance for the replacement of the conventional high-power lasers in applications of laser machining, non-linear optics and laser plasma. For the other fiber laser applications, such as CW output, Q-switched with ns pulse duration, mode-locked with fs pulse duration and fiber amplifiers, become mature recently. Further efforts need to be devoted to achieve single-mode 10-kW, CW linear polarization, 100 mJ of pulse energy and kW level of average power. We have initially established Yb-fiber laser by using pump source with 915 nm of wavelength and 20 W of incident power, and successfully produced 9 W of lasing power with 1064 nm of wavelength in this thesis. The experimental results are verified by simulation in slope efficiency, threshold, and central wavelength. Moreover, we have also analyzed optimal efficiency in coupling power and measured the absorption coefficient of Yb fiber.