In this work, the experimental techniques of supersonic molecular beam, femtosecond laser and time-of-flight (TOF) mass spectrometry were applied to investigate the photoionizations of nitrogen and oxygen molecules under intense femtosecond laser field. By way of analyzing the TOF mass spectra and yields of fragment ions, we got the dependence of ions on the laser intensity, laser ellipticity and the laser polarizations. In combination with intense field theory, we analyzed the photoionization mechanism in detail.?
