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AMO/QO Physics Seminar


"Lasing Effect in Femtosecond
Filaments in Air
"



Dr. Pengji Ding
Ecole Polytechnique, France

ABSTRACT 

Femtosecond laser filamentation in air is a phenomenon that involves a rich family of nonlinear optic effects. Lasing effect from filaments has emerged as a new phenomenon in 2011. It has been actively studied in recent 5 years not only because of its potential applications in remote sensing techniques but also the fruitful physics involved. This talk is devoted to the study of two types of lasing effect from filament plasma generated by 800 nm femtosecond laser pulses in air or pure nitrogen. The first is the bidirectional amplified spontaneous emission at 337 nm wavelength of neutral nitrogen molecules, only enabled by circularly-polarized pulses. The population inversion mechanism is attributed to inelastic electron-molecule collisions between energetic electrons and neutral nitrogen molecules on the ground state. Full characterization of both forward and backward 337 nm lasing pulse is conducted.

Another type of lasing effect is related to excited nitrogen ion, emitting at 391 nm and 428 nm wavelengths. This type of lasing effect can only be observed with linearly-polarized pump laser. It is systematically characterized in spatial, temporal and spectral domains. The temporal profile results prove that ionic lasing emission is fundamentally superradiance. A new mechanism, namely the electron recollision excitation process, is proposed for the achievement of population. It is supported by two measurements consisting of pump ellipticity and pump wavelength dependences of 391 nm lasing intensity. Numerical simulations give good agreement with the experimental observation.



Wednesday, September 21, 2016
IQSE 578, 9:00 AM
Mitchell Physics Building


Institute for Quantum Science and Engineering
Texas A&M University

(Coffee and pastries to be served 15 minutes prior start time)

Host: Marlan Scully