Ultrafast pump–probe measurement using intensity correlation of incoherent light

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Abstract
A new type of the pump–probe technique with temporally incoherent light is proposed for use in the subpicosecond and femtosecond time regions in the wide-wavelength range. This method permits measurement of the longitudinal relaxation time T1 with the time resolution determined by the characteristic time of the intensity correlation of the incident light independently of its pulse width. For a demonstration of this technique, absorption recovery time T1 = 180 psec of a dye solution was measured with Q-switched laser pulses of 150-nsec duration. Differences between this method and the corresponding one used to measure the transverse relaxation time T2 with incoherent light is discussed.