Modulation-spectrum method for measuring the amplitude and phase characteristics of optical time-dependent signals

A solution to the phase problem in optics is considered for time-varying signals, in particular, of extremely short duration. The modulation-spectrum method is used to obtain information concerning amplitude and phase variations of the optical signal. The intensity distribution is directly detected for the spectrum of the signal itself and of the signal additionally modulated in a special way. The modulation should provide a visualization of the phase information. The intensity distribution obtained makes it possible to calculate the structure of the initial signal. Three approaches toward analyzing the signals are considered in the paper. The first one is to analyze the signal whose characteristics vary in time. The second one is to study temporal optical characteristics of the medium or the object under investigation by using a probing radiation of a prescribed structure and measuring the parameters of the radiation passed through the object. The third way is to determine simultaneously the structure of the signal that varies in time and the structure of the transfer function responsible for the influence of the medium, object, or optical system on the propagating signal.