Kearney Sean P
Appl Opt. 2014 Oct 1;53(28):6579-85. doi: 10.1364/AO.53.006579.
A simple spectral focusing scheme for bandwidth optimization of gas-phase rotational coherent anti-Stokes Raman scattering (CARS) spectra is presented. The method is useful when femtosecond pump/Stokes preparation of the Raman coherence is utilized. The approach is of practical utility when working with laser pulses that are not strictly transform limited or when windows or other sources of pulse chirp may be present in the experiment. A delay between the femtosecond preparation pulses is introduced to shift the maximum Raman preparation away from zero frequency and toward the Stokes or anti-Stokes side of the spectrum with no loss in total preparation bandwidth. Shifts of 100 cm(-1) or more are attainable and allow for enhanced detection of high-energy (150-300 cm(-1)) rotational Raman transitions at near-transform-limited optimum sensitivity. A simple theoretical treatment for the case of identical pump and Stokes pulses with linear frequency chirp is presented. The approach is then demonstrated experimentally for typical levels of transform-limited laser performance obtained in our laboratory with nonresonant CARS in argon and Raman-resonant spectra from a lean H2 air flat flame.
提出了一种用于优化气相旋转相干反斯托克斯拉曼散射（CARS）光谱带宽的简单光谱聚焦方案。当利用飞秒泵浦/斯托克斯脉冲制备拉曼相干时，该方法很有用。当使用的激光脉冲不是严格的变换极限脉冲，或者实验中可能存在窗口或其他脉冲啁啾源时，该方法具有实际应用价值。引入飞秒制备脉冲之间的延迟，将最大拉曼制备从零频率移向光谱的斯托克斯或反斯托克斯一侧，而总制备带宽没有损失。可以实现100 cm⁻¹ 或更大的位移，并能以接近变换极限的最佳灵敏度增强对高能（150 - 300 cm⁻¹）旋转拉曼跃迁的检测。给出了具有线性频率啁啾的相同泵浦和斯托克斯脉冲情况下的简单理论处理。然后，针对在我们实验室中通过氩气中的非共振CARS以及贫氢空气扁平火焰的拉曼共振光谱获得的典型变换极限激光性能水平，对该方法进行了实验验证。
