In this thesis, a home made chirp-controlled pump-probe measurement system has been developed and is used to explain possible mechanism of THz radiation enhancement under positive chirped incident pulse. The chirp-controlled pump-probe measurement system with temporal resolution of around 100 femtosecond and chirp parameter tuning from ¡V350 fs2 to +650 fs2 is demonstrated. Meanwhile, using chirp-controlled pump-probe measurement system, ultrafast dynamics of photogenerated carrier in low-temperature growth GaAs in different chirp by is characterized. The relaxation time of low-temperature growth GaAs in positive chirp pump pulse is 461fs and shorter than one, which is 497fs, in negative chirp pump pulse. The result is explained by the Pump-Dump process in negative chirp pump pulse and similar band-filling effect in positive chirp pump pulse.

In this thesis, a home made chirp-controlled pump-probe measurement system has been developed and is used compare the time-resolved photo-reflectance measurements of GaAs:O with different fabricated condition(2.5¡Ñ10^13 ions/cm^2 (500Kev & 800Kev), 4¡Ñ10^13 ions/cm^2 (1200Kev) and 6¡Ñ10^13 ions/cm^2 (500Kev & 800Kev), 1¡Ñ10^14 ions/cm^2 (1200Kev)).The lower-dose sample were annealed at 0,350,400,450,550 and 600¢J,respectively. The higher-dose sample were annealed at 550¢J. The chirp-controlled pump-probe measurement system with temporal resolution of around 100 femtosecond and chirp parameter tuning from ¡V539 fs^2 to +663 fs^2 is demonstrated. Meanwhile, using chirp-controlled pump-probe measurement system, ultrafast dynamics of photogenerated carrier in GaAs:O in different chirp by laser pulse is characterized.