Abstract

    Echo phenomenon is ubiquitous in nature, with the most common example of an acoustic wave reflected by the rocks: the sound echo. Echo effects have been observed in various domains of physics, ranging from the famous nuclear spin echo in NMR spectroscopy and imaging [1], and its optical analogue of photon echo [2], and even the electron-beam echo in particle-accelerator and synchrotron radiation [3]. Recently a new kind of echoes was discovered in the rotational motion of molecules: the rotational alignment echoes, with a series of interesting physics and fascinating applications such as fractional, imaginary and rotated echoes, and the echo-enabled rephasing of molecular centrifugal distortions [4-6].

In this report, I will introduce our recent works in utilizing rotational echoes to measure ultrafast collisional dissipation in high-pressure gases [7]. The formation of rotational echoes is first explained by a classical phase-space model with emphasis about the complex dependence of rotational echoes on the two excitation laser pulses, which is in sharp contrast to the spin/photon echoes observed in inhomogeneously broadened two-level systems. By a smart control of the second laser pulse, the rotational echoes are successfully applied to measure the ultrafast collisional dissipation in high-pressureCO₂gases andCO₂-He gas mixtures until 50 bar. The extracted decay rates corroborate the dominance of inelastic collisions during the collisional dissipation of molecules, and a natural and tempting extension of the present method would thus be to carry similar investigations in the liquid phase for which any rotational information or coherence imprinted in the system has vanished due to very quick thermalization at time scales of a few ps.

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[3] D. Xiang, E. Colby, M. Dunning, S. Gilevich, C. Hast, K. Jobe, D. McCormick, J. Nelson, T. O. Raubenheimer, K. Soong, G. Stupakov, Z. Szalata, D. Walz, S. Weathersby, M. Woodley, and P.-L. Pernet, Phys. Rev. Lett. 105, 114801 (2010).

[4] G. Karras, E. Hertz, F. Billard, B. Lavorel, J.-M. Hartmann, O. Faucher, E. Gershnabel, Y. Prior, and I. S. Averbukh, Phys. Rev. Lett. 114, 153601 (2015).

[5] K. Lin, P. Lu, J. Ma, X. Gong, Q. Song, Q. Ji, W. Zhang, H. Zeng, J. Wu, G. Karras, G. Siour, J.-M. Hartmann, O. Faucher, E. Gershnabel, Y. Prior, and I. S. Averbukh, Phys. Rev. X 6, 041056 (2016).

[6] D. Rosenberg, R. Damari, S. Kallush, and S. Fleisher, J. Phys. Chem. Lett. 8, 5128 (2017).

[7] H. Zhang, B. Lavorel, F. Billard, E. Hertz, O. Faucher, J. Ma, J. Wu, E. Gershnabel, Y. Prior, and I. S. Averbukh, Phys. Rev. Lett. (2019), in press.

                                                                                   Biography

    张海粟，2014年8月博士毕业于中科院上海光机所强光实验室，随后于2015-2016年在希腊克里特的先进技术研究院(Foundation for Research and Technology-Hellas) 从事飞秒激光直写光子晶体的研究，2016年底开始在法国勃艮第大学(Université de Bourgogne)交叉学科实验室从事博士后工作，主要研究方向为飞秒激光操控分子取向和多模光纤中四波混频。目前研究兴趣包括分子转动回波现象(rotational echo)及其经典-量子对应，以及强场电离诱导产生空气激光(Air-lasing)中分子转动效应的理论模拟。