轴向隐失波激励的回音壁模式光纤激光器

Longitudinal Evanescent-Wave Pumped Whispering-Gallery-Mode Fibre Laser

采用轴向隐失波激励增益的方式,使激光增益区域局限在光纤回音壁模式的模场区域内,显著地降低了回音壁模式光纤激光辐射的抽运阈值,由此形成一种低阈值的回音壁模式光纤激光器。在微焦耳量级的低抽运能量条件下,用回音壁模式光纤激光器研究了激光染料的浓度效应。实验结果表明,随着激光染料浓度的增加,回音壁模式激光辐射的波长向长波方向移动,激光波长范围变宽。用回音壁模式染料激光的四能级模型得到激光上能级和所有能级上的分子数比值γ(λ)曲线后,很好地解释了实验结果。低抽运阈值的回音壁模式光纤激光器,为研究液体激光现象提供了极为便利的手段。

A new kind of low threshold optical fiber laser has been fabricated by immersing a fused silica optical fiber into a low refractive index dye solution. Pumped by evanescent wave along the fiber axis, dye gain is confined in the evanescent field of whispering gallery mode （WGM） of the fiber, which leads to a low pumping threshold for lasing emission. The concentration effects in liquid dye lasing emission have been studied via a WGM fibre laser under the pumping energy of 50 μJ. The results show that with the increase of rhodamine 6G dye concentration in ethanol alcohol, lasing wavelength is red shifted and lasing wavelength range is widened. The experimental observations are well explained by the 7（2） curve, a ratio of molecular density for the upper and total lasing energy levels, which is deduced from the four-energy level model of dye lasing from a WGM fibre laser. The low threshold optical fiber laser provides a convenient way to study liquid dye lasing phenomenon.