Geng Jihong, Wang Qing, Jiang Shibin
AdValue Photonics, 3708 E Columbia Street, Suite 100, Tucson, Arizona 85714, USA.
Appl Opt. 2012 Mar 1;51(7):834-40. doi: 10.1364/AO.51.000834.
Broadband mid-infrared supercontinuum pulses were generated directly from a short piece of active fiber in a single-mode Tm-doped fiber amplifier. The broadband mid-infrared pulses have an extremely high spectral flatness with 600 nm FWHM bandwidth (from 1.9 μm to 2.5 μm), >15 kW peak power, and >20 GW/cm(2) laser peak intensity. This new approach exhibits a significantly different physical mechanism from other supercontinuum generation demonstrations in the literature, in which usually a piece of passive fiber was used for nonlinear spectral broadening. The physical mechanism for the broadband mid-infrared supercontinuum generation in this approach has been attributed to a combined effect of two superradiative processes of Tm(3+) ions (i.e., the (3)F(4)-(3)H(6) transition covering the 1.82.1 μm spectral region and the (3)H(4)-(3)H(5) transition covering the 2.2~2.5 μm spectral region), and also nonlinear optical processes as well in the Tm-doped gain fiber. The spectra of the mid-infrared supercontinuum pulses were further broadened in a 2 m chalcogenide fiber with 20 dB bandwidth ~1100 nm and a 3 m fluoride fiber with 20 dB bandwidth ~2600 nm.
宽带中红外超连续谱脉冲直接由单模掺铥光纤放大器中的一小段有源光纤产生。宽带中红外脉冲具有极高的光谱平整度，半高全宽带宽约为600nm（从1.9μm至2.5μm），峰值功率大于15kW，激光峰值强度大于20GW/cm²。这种新方法展现出与文献中其他超连续谱产生演示显著不同的物理机制，在那些演示中通常使用一段无源光纤进行非线性光谱展宽。这种方法中宽带中红外超连续谱产生的物理机制归因于铥离子（Tm³⁺）的两个超辐射过程的联合效应（即覆盖1.82.1μm光谱区域的³F₄ - ³H₆跃迁和覆盖2.22.5μm光谱区域的³H₄ - ³H₅跃迁），以及掺铥增益光纤中的非线性光学过程。中红外超连续谱脉冲的光谱在一根2m长、20dB带宽约为1100nm的硫系光纤和一根3m长、20dB带宽约为2600nm的氟化物光纤中进一步展宽。
