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

超快激光脉冲具有宽波长可调谐性，在许多科学和工业应用中具有决定性的优势。然而，现今最常用的产生这种脉冲的技术，例如，光学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，本质上需要庞大且昂贵的设备，同时仍然不能互变地保证无间隙可调谐性。而且，输出脉冲的持续时间保持在初始泵浦激光器的水平，使得需要增加进一步的复杂性以实现更短的持续时间。在此背景下，我们开发了一种简单而经济的系统来产生波长可调谐的光脉冲，其额外的好处是脉冲持续时间比用作泵浦的放大激光器的脉冲持续时间短。（由自相位调制或受激拉曼散射引起的）气体填充空芯光纤（HCF）中的拉曼散射，然后是随后的光学滤波阶段。一旦最外层的光谱瓣（其可以通过改变气体压力来调谐）是从通过光学滤波的加宽的输出光谱中选择的，直接获得准变换极限脉冲，能量转换效率约为10- 15（与商业光学参量放大器相当）和脉冲持续时间比泵浦激光器的脉冲持续时间短3-4倍。根据最近的市场评估报告，一些公司和研究人员已经对这种新开发的可调系统表现出极大的兴趣。该NSERC I2 I第一阶段项目现在有可能大大提高我们的技术的商业价值，通过针对以下3个目标：（i）设计一个更紧凑的系统，其特点是HCF（< 2 m）比以前使用的（~ 6 m）更短，这一解决方案显然更有利于实际应用;（ii）开发一种实用的可调谐光谱滤波仪器，采用折叠式4-f布局;以及（iii）演示市场研究中确定的一种简单应用：一种方便的太赫兹光谱学装置，其采用由经滤波的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.