We demonstrate the generation of sub-6-fs pulses centered at 405 nm by frequency doubling of 8.6-fs Ti:sapphire laser pulses. The frequency doubling is carried out in a nonlinearly chirped quasi-phase-matching grating fabricated in a lithium tantalate substrate. This device simultaneously provides frequency conversion and pulse compression of the positively prechirped fundamental pulses. The second-harmonic pulses are characterized in a cross-correlation setup, and their pulse shapes are retrieved by two iterative phase-reconstruction algorithms. The generated second-harmonic spectrum spans a bandwidth of 220 THz. To our knowledge, these are the shortest pulses ever generated in the blue spectral region.
© 2001 Optical Society of America
L. Gallmann, G. Steinmeyer, U. Keller, G. Imeshev, M. M. Fejer, and J.-P. Meyn, "Generation of sub-6-fs blue pulses by frequency doubling with quasi-phase-matching gratings," Opt. Lett. 26, 614-616 (2001)