Fortunately, techniques exist that monitor the spectral profile of a pulse as a function of time. These techniques allow for the complete reconstruction of the electric field. Of these techniques, frequency-resolved optical gating (FROG) is arguably the most straightforward and easiest to implement. As mentioned earlier, FROG allows for full phase retrieval of the input field without the ambiguity associated with autocorrelation. Our Amplitude and Phase Characterization of Ultrashort Laser Pulses application note presents a simple, low dispersion, easy-to-use, general purpose FROG device that can readily be implemented on the Newport Long Scan Autocorrelator platform as described in Application Note 27.

Second harmonic FROG (SHG FROG) geometries are the only real option for ultrafast oscillators. An SHG FROG is simply a spectrally resolved autocorrelator. Although the sign of the spectral phase is lost in the measurement, efficient algorithms exist which can deduce the order and magnitude of the spectral phase where the sign can be determined if need by performing additional measurements. (Rick Trebino, "Frequency-Resolved Optical Gating: The Measurement of Ultrafast Laser Pulses", Norwell, MA, Kluwer Academic Publishers (2000)) If planning to use the standard kit with an oscillator, a BBO crystal used to generate the second harmonic – such as Newport model 90015087 (covering input wavelength range of 700-2000 nm) and/or 90015088 (480-700 nm) – must also be purchased separately.