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《科学前沿报告会》 第260期

科学前沿报告会(260)

报告题目

Photodetachment dynamics of negative ions by femtosecond laser pulses

报 告 人

Francesca Shearer, Queen's University Belfast, U.K.

报告地点

物理楼中508

报告时间

9月10日 (星期三) 上午9:30-10:30

联 系 人

彭良友(6276 5027)

报告摘要

We consider photodetachment of negative ions by linearly and circularly polarized femtosecond laser pulses. Our proposed model will employ the adiabatic saddle point approach of Keldysh [Sov. Phys. JETP 20, 1307 (1965)]. It should be noted in our framework we neglect the rescattering mechanism since we are considering direct photodetachment only. This restricts us to the low-energy part of the photodetachment spectrum. We apply the theory to consider numerical calculations for mid-infrared laser wavelengths for H-, F-, and Si- negative ions. The behaviour of the electron momentum saddle point distributions in the complex-time plane is analysed for the various negative ions. Photoelectron momentum maps of the direct electrons are also simulated and exhibit a characteristic structure dependent on the symmetry of the initial state. Within the current model these structures can be interpreted as due to both electron wave packet interferences in a time domain and by multiphoton absorption in a frequency domain. Photoangular distributions (PADs) are calculated and bifurcation effects associated with channel closings are observed as the laser-field frequency and intensity pass through ponderomotive-potential induced channel closures. Interference effects in each negative ion considered are observable as nonmonotonic structures arising from coherent electronic wavepackets. Additionally CEP effects are noted to influence all the photoelectron emission spectra considered where few-cycle pulses are used in the calculations. Our results are compared with existing available experimental and theoretical data.

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