Modulation of non-adiabatic alignment of N<sub>2</sub> molecule by femtosecond laser pulses

The alignment of molecules in the femtosecond laser field induces refractive index propagation medium to change, resulting spectral modulation effect. In this paper, time evolution wavelength offset a probe pulse under influence non-adiabatic molecular and Kerr effect is measured experimentally by pump-probe method nitrogen medium, degree N<sub>2</sub> obtained. By solving time-dependent Schrödinger equation theoretically, expression obtained, calculated. Taking into account combined on change birefringence spectrum achieved. experimental result accords well with theoretical calculation, demonstrating that results obtained measurement can be used characterize degree. Further, double pump control alignment. It found enhanced method. Moreover, adjusting delay between two pulses, is, adding second at one rotational period half period, respectively, enhancement loss achieved, which named “alignment switch” induced also applied other systems different anti-alignment times, such as CO<sub>2</sub> O<sub>2</sub> molecules, indicating universally.