Tu Haohua, Boppart Stephen A
Biophotonics Imaging Laboratory, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Opt Express. 2009 Sep 28;17(20):17983-8. doi: 10.1364/OE.17.017983.
Cherenkov radiation from short photonic crystal fiber with a high air-fill fraction can selectively convert the 1020 nm fs pump pulses from a laser oscillator to the fundamental-mode signal pulses at a significantly shorter wavelength. Across the ultraviolet-visible spectral region, the typical fiber output is characterized by a single isolated Cherenkov band having a multimilliwatt-level average power, a Gaussian-shaped spectrum, and a 3-dB bandwidth of 15 nm. By selecting photonic crystal fibers with smaller cores, the central wavelength of the Cherenkov band can be easily extended to 347 nm in the ultraviolet, in sharp contrast to various supercontinuum or non-supercontinuum fiber sources that have difficulty extending their emission spectra below 400 nm. The supercontinuum generation often associated with fs pulse-pumped fibers is efficiently suppressed by detuning the zero-dispersion wavelength of the photonic crystal fiber far shorter than the pump wavelength, a condition termed as the short nonlinear-interaction condition.
具有高空气填充率的短光子晶体光纤产生的切伦科夫辐射能够将激光振荡器输出的1020纳米飞秒泵浦脉冲选择性地转换为波长显著更短的基模信号脉冲。在紫外-可见光谱区域，典型的光纤输出表现为具有多毫瓦级平均功率、高斯形状光谱以及15纳米3分贝带宽的单个孤立切伦科夫带。通过选择纤芯更小的光子晶体光纤，切伦科夫带的中心波长能够轻松扩展至紫外波段的347纳米，这与各种难以将其发射光谱扩展至400纳米以下的超连续或非超连续光纤光源形成鲜明对比。通过将光子晶体光纤的零色散波长调谐至远低于泵浦波长，即所谓的短非线性相互作用条件，通常与飞秒脉冲泵浦光纤相关的超连续谱产生被有效抑制。
