UV femtosecond laser pulse was used to excite the ultrafast carrier dynamics inside the Al<sub>2</sub>O<sub>3</sub>/SiO<sub>2</sub>
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 Al<sub>3</sub>O<sub>2</sub> 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.