System for the Generation of Tunable Ultrafast Optical Pulses (Phase I)

具有宽波长可调谐特性的超快激光脉冲在许多科学和工业应用中具有决定性的优势。然而，目前最常用的产生这种脉冲的技术，例如光参量放大，需要用于频率转换和放大的多个光学非线性过程，基本上需要笨重和昂贵的设备，同时仍然不能自动保证无间隙可调谐。此外，输出脉冲的持续时间保持在初始泵浦激光的水平，因此需要进一步增加复杂性以获得更短的持续时间。在这种情况下，我们开发了一种简单且经济有效的系统来产生波长可调的光脉冲，并且具有比用作泵浦的放大激光器的脉冲持续时间更短的脉冲持续时间。我们的策略基于充气空芯光纤(HCF)中的非线性光谱展宽(由自相位调制或受激励的拉曼散射引起)，随后是光学滤波级。一旦通过光学滤波从展宽的输出光谱中选择最外面的光谱波瓣(可以通过改变气体压力来调谐)，直接获得准变换受限脉冲，能量转换效率约为10-15%(与商用光参量放大器相当)，脉冲持续时间比泵浦激光短3-4倍。根据最近的一份市场评估报告，几家公司和研究人员已经对这种新开发的可调系统表现出了浓厚的兴趣。NSERC I2I第一阶段项目现在有可能极大地提高我们技术的商业价值，目标如下：(I)设计一个更紧凑的系统，具有比以前使用的(~6 m)更短的HCF(&lt；2 m)，这一解决方案显然更适合实际实施；(Ii)开发基于折叠4-f布局的实用可调光谱滤光器；以及(Iii)展示市场研究中确定的一个简单应用：一种方便的太赫兹光谱分析装置，使用由过滤脉冲直接泵浦的有机晶体。

Ultrafast laser pulses featuring broad wavelength tunability can bring a decisive advantage in numerousscientific and industrial applications. However, nowadays the most commonly implemented technologies togenerate such pulses, e.g., optical parametric amplification, necessitate multiple optical nonlinear processes forfrequency conversion and amplification, essentially requiring bulky and expensive apparatus while still notautomatically guaranteeing a gap-free tunability. Also, the time duration of the output pulses remains at thelevel of the initial pump laser, so that further complexity needs to be added to achieve shorter durations. In thiscontext, we have developed a simple and cost-effective system to generate wavelength-tunable optical pulses,with the additional benefit of a pulse duration shorter than the one of the amplified laser employed as a pump.Our strategy is based on nonlinear spectral broadening (arising from self-phase modulation or stimulatedRaman scattering) in a gas-filled hollow-core fiber (HCF), followed by a subsequent optical filtering stage.Once the outermost spectral lobe (which can be tuned by varying the gas pressure) is selected from thebroadened output spectrum by optical filtering, quasi-transform-limited pulses are directly obtained withenergy conversion efficiencies of about 10-15% (comparable with commercial optical parametric amplifiers)and pulse durations 3-4 times shorter than the one of the pump laser. According to a recent market assessmentreport, several companies and researchers have already shown a significant interest in such newly-developedtunable system. This NSERC I2I Phase I project has now the potential to greatly increase the commercial meritof our technology, by targeting the following 3 objectives: (i) devising a more compact system featuring ashorter HCF (< 2 m) than the one previously utilized (~ 6 m), a solution clearly more favorable for realisticimplementations; (ii) developing a practical tunable spectral filtering apparatus based on a folded 4-f layout;and (iii) demonstrating a straightforward application identified in the market study: a convenient terahertzspectroscopy setup employing an organic crystal directly pumped by the filtered pulses.