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Phys Rev Lett. 2019 Feb 8;122(5):053202. doi: 10.1103/PhysRevLett.122.053202.

Detecting and Characterizing the Nonadiabaticity of Laser-Induced Quantum Tunneling.

Liu K1,2, Luo S1, Li M1, Li Y1, Feng Y1, Du B1, Zhou Y1, Lu P1,3, Barth I2.

Author information

1
Wuhan National Laboratory for Optoelectronics and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China.
2
Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle (Saale), Germany.
3
Hubei Key Laboratory of Optical Information and Pattern Recognition, Wuhan Institute of Technology, Wuhan 430205, China.

Abstract

The nonadiabaticity of quantum tunneling through an evolving barrier is relevant to resolving laser-driven dynamics of atoms and molecules at an attosecond timescale. Here, we propose and demonstrate a novel scheme to detect the nonadiabatic behavior of tunnel ionization studied in an attoclock configuration, without counting on the laser intensity calibration or the modeling of the Coulomb effect. In our scheme, the degree of nonadiabaticity for tunneling scenarios in elliptically polarized laser fields can be steered continuously simply with the pulse ellipticity, while the critical instantaneous vector potentials remain identical. We observe the characteristic feature of the measured photoelectron momentum distributions, which matches the distinctive prediction of nonadiabatic theories. In particular, our experiments demonstrate that the nonadiabatic initial transverse momentum at the tunnel exit is approximately proportional to the instantaneous effective Keldysh parameters in the tunneling regime, as predicted theoretically by Ohmi, Tolstikhin, and Morishita [Phys. Rev. A 92, 043402 (2015)PLRAAN1050-294710.1103/PhysRevA.92.043402]. Our study clarifies a long-standing controversy over the validation of the adiabatic approximation and will substantially advance studies of laser-induced ultrafast dynamics in experiments.

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