Abstract
The polarization evolution and control of a femtosecond laser pulse in the wake of molecular alignment inside a laser filament was investigated. A weak probe pulse was delayed with respect to the field-free revivals of the pre-excited rotational wave-packets created by an infrared filamenting pulse in nitrogen gas. 30° was set between the pump and probe's initial linear polarization directions in order to control the output probe's polarization ellipse. The detailed physical response of the probe's polarization states was analyzed in the wake of alignment and dephasing of molecular N(2). The probe's polarization was modulated by varying the retarded time between the pump and probe pulses.
Highlights
Filamentation induced birefringence in isotropic gas media has attracted increasing attentions owing to its remarkable effects on the spatial and spectral reshaping of a probing pulse [1,2,3,4]
The ultrafast birefringence was quantified by measuring the filament-induced polarization change of a probe pulse [5,6,7,8]
Besides this instantaneous electronic response, a delayed birefringence was induced by the molecular alignment and revivals
Summary
Filamentation induced birefringence in isotropic gas media has attracted increasing attentions owing to its remarkable effects on the spatial and spectral reshaping of a probing pulse [1,2,3,4]. The ultrafast birefringence was quantified by measuring the filament-induced polarization change of a probe pulse [5,6,7,8]. The molecular alignment induced birefringence could be measured by means of the weak-field probe polarization technique with 45° between the initially linearly polarized pump and probe pulses [9, 10] or by making use of the spatial crossdefocusing effect of the probe pulse through fixing the pump and probe polarization crossed with each other [11, 12]. The ultrafast birefringence was quantified in argon by measuring the filamentinduced polarization rotation of a probe pulse [6]. Detailed measurement of the response of the probe’s polarization states caused by molecular alignment induced delayed birefringence has been left aside to date. The polarization property of the probe pulse could be controlled
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