Sub-5 fs optical pulse characterization

Abstract

Ultrabroadband optical pulses generated throughself-phase and induced-phase modulation effects and ultrashortoptical pulses whose phases were compensated for using a 4fpulse shaper with a spatial phase modulator were generated.Interferometric autocorrelation, frequency-resolved optical gatingand spectral phase interferometry for direct electric-fieldreconstruction (SPIDER) measurements were made to characterizethese pulses, and the results were compared. The generation of5.0 fs (2.4 cycle) or shorter optical pulses was confirmed. Formuch shorter pulses, below-two-cycle or monocycle optical pulses,single-shot characterization excluding the errors due to thepulse-to-pulse fluctuation is essential. The sensitivity ofSPIDER, which is the most advantageous characterization techniqueapart from its low sensitivity, was improved by a factor of abouta hundred (~1 nJ/THz-bandwidth). Instead of achirped reference pulse split from the pulse to be characterized,a powerful external pulse from a Ti:sapphire laser amplifier asa highly intensive chirped pulse was employed. By use of thismodified SPIDER, the characterization of an over-one-octaveultrabroadband optical pulse was performed. This modified-SPIDERmethod is the most promising for characterization of monocycleoptical pulses.