| Summary: | 碩士 === 國立交通大學 === 光電工程所 === 88 === This thesis researchs the infuences of semicondutcor saturable absorber mirror (SESAM) to femtosecond laser pulse shaping and chirp effects. The nonlinear reflectivity of SESAM are calibrated under three chirp conditions (positive chirp, negative chirp, and transform-limited) and the satruation fluences are calculated by the saturable absorption model. We find that the saturation fluence under negaticve chirp condition is 2-order smaller than those under other two conditons. Then We observe the shaping and chirp effects of laser pulses directly by spectrally two-beam coupling technique. Under transform-limited condition, SESAM have great influences to laser pulse shaping and chirp effect. Additionally, exciton re-emssion is observed. We explain these results qualitatively by a simple model. When SESAM interacted with incident pulses, the timing between the free carrier plasma and ionization of exciton vary the saturation fluence of SESAM. The negative chirp contriubuted by exciton is larger than positive chirp contributed by free carrier. So SESAM will effectly induce the positive chirp to laser pulses.
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