The characterization of femtosecond optical pulses for Ti:sapphire laser output is conducted with two photon induced transitions in blue light emitting diodes. Excellent phase relationship between the two separated pulses are recorded from the fringes of the two photon induced, second order correlation function. It is demonstrated that the two-photon induced current can greatly simplify the femtosecond pulse characterization by direct converting the photon signal to current signal.