In nonlinear optics, a major challenge is to maximize the interaction between the light from laser sources and low-density media such as gases. An ultrafast laser beam can be focused to form a highly intense spot over a small concentrated area. The ultrafast laser beam has a short pulse width of less than one picosecond and high peak power in the beam profile (Fig. 1). The beam profile of the laser source describes the energy density and distribution of light, and the beam profile of a laser source is usually affected during the propagation and collimation of the beam. An efficient nonlinear optical sensor also requires high peak power at low energy (low average power) over short duration of laser pulse, a high beam profile and long interaction length. These requirements of a nonlinear optical sensor with low attenuation constant can be achieved in hollow-core photonic crystal fiber (HC-PCF). Gas-filled HC-PCF exhibits optical nonlinearity for an ultrashort temporal and spectral broadening of NIR pulses [1], [2]. The nonlinearity in HC-PCF can be achieved by tuning the gas pressure. Gas-filled HC-PCF nonlinear media are low-cost, replenishable, reconfigurable and exhibit sharp spectral lines [3]. Linear and nonlinear responses are also found in other types of optical fibers.

中文翻译：

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太赫兹机制中空心反谐振光纤传感器的线性度和非线性度

在非线性光学中，一个主要挑战是最大化来自激光源的光与气体等低密度介质之间的相互作用。超快激光束可以聚焦在一个小的集中区域上形成一个高强度的光斑。超快激光束具有小于 1 皮秒的短脉冲宽度和光束轮廓中的高峰值功率（图 1）。激光源的光束轮廓描述了光的能量密度和分布，激光源的光束轮廓通常在光束的传播和准直过程中受到影响。高效的非线性光学传感器还需要在短激光脉冲持续时间、高光束轮廓和长相互作用长度内以低能量（低平均功率）获得高峰值功率。具有低衰减常数的非线性光学传感器的这些要求可以在空心光子晶体光纤 (HC-PCF) 中实现。气体填充的 HC-PCF 表现出光学非线性，用于 NIR 脉冲的超短时间和光谱展宽 [1]、[2]。HC-PCF 的非线性可以通过调节气体压力来实现。充气的 HC-PCF 非线性介质成本低、可补充、可重新配置，并且显示出尖锐的谱线 [3]。在其他类型的光纤中也发现了线性和非线性响应。可重构并表现出尖锐的谱线 [3]。在其他类型的光纤中也发现了线性和非线性响应。可重构并表现出尖锐的谱线 [3]。在其他类型的光纤中也发现了线性和非线性响应。