The Complete Measurement Of Ultrashort Pulse Based On Frequency-resolved Optical Gating

Measuring ultrashort laser pulses has always been a challenge ever since. For many years, it was possible to create ultrashort pulses, but not to measure them. With the improvement of laser pulse creating technique, we can create femtosecond in the recent years. Traditional measuring techniques such as autocorrelation can not satisfy us now. Therefore, a lot of new solution was presented in the end of last century. Among them, a technique named frequecy-resolved optical gating(FROG) is available for measuring the amplitude and phase of pulses in various wavelength scale.In mid 1980, Ishida suggested, for the first time, that a tandem combination of an autocorrelator and a spectrometer could be used to extract both the amplitude and phase of an ultrashort pulse simultaneously. In 1993, Trebino's group implemented the frequency-resolved optical gating(FROG) measurement for the first time. FROG is a revolution to the ultrashort pulse characterization by giving both intensity and phase of any instantaneous ultrashort pulse.The paper introduces the theory of FROG, and present an improved algorithm for retrieving the amplitude and phase of an ultrashort laser pulse. We calculate the FROG trace of initial guess pulse, program the computer to retrieve to the amplitude and phase of the pulse. It is proved our algorithm is available for various initial guess. We also add noise in FROG trace, and still get good results. We give the retrieved results got by the program and our development of the traditional algorithm and analyze the measuring error. The algorithm was tested to be robust and handy for diagnosing ultrashort pulses with varying characteristics completely.Moreover, for further improvement of accuracy and completeness, we present a possible to combine FROG and digital holography, and analyze its algorithm. It is proved to be available in theory.