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.