Study On The Alignment Of N₂O Molecules In Femtosecond Laser Field

Research on the effects of varying laser pulse free parameters and rotational temperature on the alignment of N₂O molecules by using a single femtosecond one-color laser pulse as well as double one-color laser pulses is performed.In the first place,a single pulse is adopted.By changing values of rotational temperature and free parameters of a single laser pulse,i.e.width and intensity,influences on N₂O alignment were discussed in three cases: 1)change wavelength and fix laser intensity and temperature;2)while the laser wavelength and temperature being constant,change the laser intensity;3)only change rotational temperature while the laser wavelength and laser intensity keep invariant.The results show that: molecular alignment can be enhanced or suppressed by tuning the laser wavelength,laser intensity or rotational temperature finely.However,when using a single laser pulse,the alignment of N₂O will be enhanced in the beginning then suppressed in the end by increasing laser intensity continually with immutable laser pulse width and rotational temperature.This is because excessive laser fields can lead to ionization or dissociation of molecules and produce upper harmonics,which will impact the alignment.Therefor different pulse intensity corresponds to different saturation intensity which will maximize the alignment of N₂O.We subsequently investigate the maximization of N₂O alignment in case of double one-color laser pulses.Given a fixed rotational temperature,a fixed pulse width,and the sum of the intensities of two femtosecond onecolor laser pulse is equal to the saturation intensity,we attempted to improve the alignment of N₂O molecules by adjusting the delay time of the two pulse.According to the further calculation,it is confirmed that the strong field effect can be relieved by replace single one-color laser pulse to double one-color laser pulses.Moreover,adopting two femtosecond one-color laser pulse and adjusting their delay time will further increase the degree of alignment of N₂O.