A method determining a transient response includes providing a measured magnitude of the Fourier transform of a complex electric field temporal profile of a pulse sequence comprising a probe pulse and a dummy pulse, wherein the probe pulse is indicative of the transient response of a sample. The method further includes providing an estimated phase term of the Fourier transform of the complex electric field temporal profile of the pulse sequence and multiplying the measured magnitude and the estimated phase term to generate an estimated Fourier transform of the complex electric field temporal profile of the pulse sequence. The method further includes calculating an inverse Fourier transform of the estimated Fourier transform, wherein the inverse Fourier transform is a function of time, and calculating an estimated complex electric field temporal profile of the pulse sequence by applying at least one constraint to the inverse Fourier transform.