Sarkar Chitrakshya, Bhattacharya Rangana, Bhattacharyya S S, Saha Samir
Atomic and Molecular Physics Section, Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India.
J Chem Phys. 2007 Sep 14;127(10):104304. doi: 10.1063/1.2775448.
We have theoretically investigated the population transfer from the initial ground rovibrational level v(g)=0, J(g)=0 to the final rovibrational levels v(f)=1,2, J(f)=0 of the ground electronic state X (1)Sigma(g) (+) via the resonant intermediate level v(i)=6, J(i)=0 of the excited electronic state EF (1)Sigma(g) (+) of H(2) molecule by (2+2)-photon stimulated hyper-Raman passage (STIHRP). The density matrix technique has been employed to evaluate the population transfer to the final target levels using linearly chirped pump and Stokes laser pulses with different chirp rates. Both the pulses are considered to have the same temporal shape, pulse width, and linear parallel polarizations. We have studied in detail the dependence of the population transfer on the set of laser parameters for pulse (peak) intensities in the ranges of 1.5 x 10(11)-1.0 x 10(12) and 1.0 x 10(12)-7.0 x 10(12) W/cm(2). The corresponding pulse widths (full width at half maximum) are of the order of 115-200 and 15-30 ps. We have found that the chirp rate parameters can be optimized to achieve almost complete population transfer from the ground (g) to the final (f) target levels. This, to our knowledge, is the first application of a (2+2)-photon STIHRP process with chirpings to a model molecular system (H(2)). The study demonstrates the suitability of the chirped (2+2)-photon STIHRP technique for selective and almost total inversion of vibrational population in a diatomic molecule.
我们从理论上研究了通过（2+2）-光子受激超拉曼跃迁（STIHRP），使H₂分子基电子态X¹Σg⁺的初始基振转能级v(g)=0、J(g)=0到最终振转能级v(f)=1、2、J(f)=0的布居转移，其中间共振能级为激发电子态EF¹Σg⁺的v(i)=6、J(i)=0。利用密度矩阵技术，通过具有不同啁啾率的线性啁啾泵浦光和斯托克斯激光脉冲，评估到最终目标能级的布居转移。两个脉冲具有相同的时间形状、脉冲宽度和线性平行偏振。我们详细研究了布居转移对脉冲（峰值）强度在1.5×10¹¹-1.0×10¹²和1.0×10¹²-7.0×10¹²W/cm²范围内的一组激光参数的依赖性。相应的脉冲宽度（半高全宽）约为115-200和15-30 ps。我们发现，可以优化啁啾率参数，以实现从基态（g）到最终（f）目标能级几乎完全的布居转移。据我们所知，这是啁啾（2+2）-光子STIHRP过程首次应用于模型分子系统（H₂）。该研究证明了啁啾（2+2）-光子STIHRP技术适用于双原子分子中振动布居的选择性和几乎完全反转。
