Purwar Harsh, Idlahcen Saïd, Rozé Claude, Sedarsky David, Blaisot Jean-Bernard
Opt Express. 2014 Jun 30;22(13):15778-90. doi: 10.1364/OE.22.015778.
Imaging with ultrashort exposure times is generally achieved with a crossed-beam geometry. In the usual arrangement, an off-axis gating pulse induces birefringence in a medium exhibiting a strong Kerr response (commonly carbon disulfide) which is followed by a polarizer aligned to fully attenuate the on-axis imaging beam. By properly timing the gate pulse, imaging light experiences a polarization change allowing time-dependent transmission through the polarizer to form an ultrashort image. The crossed-beam system is effective in generating short gate times, however, signal transmission through the system is complicated by the crossing angle of the gate and imaging beams. This work presents a robust ultrafast time-gated imaging scheme based on a combination of type-I frequency doubling and a collinear optical arrangement in carbon disulfide. We discuss spatial effects arising from crossed-beam Kerr gating, and examine the imaging spatial resolution and transmission timing affected by collinear activation of the Kerr medium, which eliminates crossing angle spatial effects and produces gate times on the order of 1 ps. In addition, the collinear, two-color system is applied to image structure in an optical fiber and a gasoline fuel spray, in order to demonstrate image formation utilizing ballistic or refracted light, selected on the basis of its transmission time.
超短曝光时间成像通常通过交叉光束几何结构来实现。在常规配置中，一个离轴选通脉冲会在具有强克尔响应的介质（通常是二硫化碳）中诱导双折射，随后是一个偏振器，其排列方式是使沿轴成像光束完全衰减。通过适当地调整选通脉冲的时间，成像光会经历偏振变化，从而允许随时间变化的光透过偏振器形成超短图像。交叉光束系统在产生短选通时间方面是有效的，然而，信号通过该系统的传输会因选通光束和成像光束的交叉角度而变得复杂。这项工作提出了一种基于I型倍频和二硫化碳中共线光学配置相结合的稳健超快时间选通成像方案。我们讨论了交叉光束克尔选通产生的空间效应，并研究了克尔介质共线激活对成像空间分辨率和传输时间的影响，这消除了交叉角空间效应并产生了约1皮秒量级的选通时间。此外，共线双色系统被应用于对光纤和汽油燃料喷雾中的结构进行成像，以便展示利用基于传输时间选择的弹道光或折射光形成图像的过程。
