Based on the dispersion equation of principal-axis refraction index, regardless of crystal absorption and other nonlinear interactions, dispersion characteristics of femtosecond laser in monopotassium phosphate (KDP) crystal are studied. As a result of the crystal dispersion, light waves of different frequencies in the incident femtosecond laser pulse propagating in a crystal can result in different phase changes so that waveforms of resulting pulses are correspondingly changed. By numerical calculation, propagation properties of the input pulse in the crystal are obtained. It is found that the pulse width, intensity and expanding width of the output pulse depend on the crystal length, central wavelength and polarization direction of the input pulse. The results may be useful in frequency doubling, pulse shaping, development of optical crystal devices, etc.
