Experimental study on emission spectra of air plasma induced by femtosecond laser pulses

The emission spectra produced in ambient air with focused strong femtosecond laser pulses are studied experimentally. The results show the emission spectrum presents the short-wavelength continuum spectrum with stronger intensity(cutoff wavelength 340 nm) and long-wavelength line spectrum with less weak intensity(near 800 nm). A similar spectrum shape can be acquired with fixed pulse width 50 fs and adjustable laser pulse energy. When the pulse energy is 1 mJ and the pulse width increases from 50 fs to 1ps, the peak value of continuum spectrum located in 500 nm wavelength becomes strong and gradually presents the line spectrum characteristics.