UV femtosecond laser pulse was used to excite the ultrafast carrier dynamics inside the Al2O3/SiO2
high reflective mirror. Spectral shift between two different laser induced free electron absorption bands
was observed. The former one centered at 406 nm undergo a fast decay of ~2.6 ps and a longer one of
~15 ps. Accompanied by the fast decay of the first absorption band, a new absorption band centered at
396 nm grew around ~2.8 ps after the laser excitation. The probable explanation the observed spectral
shift of the free electron absorption band is that, the free carrier in the Al3O2 conductive band was
trapped into some kind of defect state, which has an absorption peak at 396 nm, at a time scale of ~2.8
ps. Since the defect state has much longer lifetime than the initial generated free carriers in thee
conductive band, probably under the condition of ultrafast high-frequency pulsed UV laser exposure,
the incubation effect will decrease the laser damage threshold of the subsequent laser pulses.
Using 9 fs UV laser pulses, laser induced ultrafast dynamics in fused silica is investigated in the present study. The free
carrier dynamics under few-cycle UV laser excitation far below laser damage threshold in the fused silica was studied.
After laser excitation, free carrier in the conductive band is found to turn into self-trapped excitons within about 300fs. It
is possible that the trapped exciton will result in the incubation effect under the condition of ultrafast high-frequency
pulsed UV laser exposure.
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