Experimental and theoretical demonstration of validity and limitations in fringe-resolved autocorrelation measurements for pulses of few optical cycles

Abstract

Using 3.6-and 5.3-fs pulses, we demonstrated theoretically and experimentally that fringe-resolved autocorrelation (FRAC) traces are distorted by bandwidth limitations of the second-harmonic generation (SHG) in 10-µm-thick, type I β -BaB 2 O 4 for pulses shorter than sub-5 fs. In addition, detailed numerical analysis of the SHG showed that the optimum crystal angle where the FRAC trace distortion becomes minimum is in disagreement not only with the phase-matching angle but also with the angle where the FRAC signal intensity becomes maximum. Furthermore, the apparent pulse duration measured at a nonoptimum angle was confirmed to become shorter than that of its transform-limited pulse, in excellent agreement with the calculated result.

Generation of 0.5 mJ, few-cycle laser pulses by an adaptive phase modulator

“…One approach to obtain the shortest pulse is to optimize the second harmonic signal by focusing the compressed white-light pulses to a nonlinear crystal. However, it was found that by optimizing the SH signal, neither genetic algorithm nor evolutionary algorithm can compress the pulse with high accuracy [19,20]. Another approach is to measure the spectral phase of the white light from the fiber and feed the measured value to the phase modulator for correction.…”

Quasi-automatic phase-control technique for chirp compensation of pulses with over-one-octave bandwidth-generation of few- to mono-cycle optical pulses

“…Such nonlinear chirp is not compensated for by conventional passive dispersion elements (for example, a grating pair, a prism pair, chirped mirrors, and their combinations) because of interrelation between second-order and higher order phase dispersions of their compensators and their bandwidth limitations. In addition, few-to mono-cycle pulses generated as a result of pulse compression cannot be characterized correctly by a conventional technique of fringe resolved autocorrelation (FRAC) owing to the so called filter effect in second-harmonic generation (SHG) processes [1]. Manuscript In recent years, high-powered pulse compression to few cycles was reported using a gas-filled hollow fiber, chirped mirrors, and an SHG frequency-resolved optical gating (SHG-FROG) measurement [2].…”

“…However, the time required to run the chirp compensation experiment for the generation of 11-fs pulses after about 1000 iterations was roughly 15 min. In addition, for shorter pulse compression in the near-octave bandwidth and few-cycle region, the SHG intensity cannot be the unique target and cannot always define a minimized pulse [1]. Fig.…”