Observation of enhanced field-free molecular alignment by two laser pulses

The experimental evidence of enhanced field-free molecular alignment was provided by two laser pulses. It was shown that the degree of field-free alignment induced by one intense pulse was improved by replacing it with two pulses containing the same total energy. The strongest double pulse alignment was found to occur shortly after the turnoff of the last pulse and was optimized when the second pulse was approximately 3 times as intense as the first pulse. The results show that it is necessary to lower the energy since the multiphoton ionization rate have a highly nonlinear dependence on the intensity.