Calibrating and removing the direction of time ambiguity in FROG

Summary form only given. Frequency resolved optical gating, FROG, has a well-proven track record for measuring ultrashort pulses. These simple devices provide complete information about both the amplitude and phase of the pulse. Like all techniques, FROG can suffer from human error in their calibration. Here we present a simple method for calibrating a FROG device. This method also has the added bonus of removing the direction of time ambiguity in an SHG FROG retrieval. We have dubbed this method the Procedure for Objectively Learning the Kalibration And Direction Of Time (POLKADOT) FROG. The POLKADOT FROG technique is based on a multiple pulse FROG trace. Calibration does not require the entire trace; it only needs the information contained in the marginals.