We present a new technique for measuring the intensity I(t) of optical
pulses using a temporal optical system. A diffraction grating pair fo
llowed by a microwave-driven, optical phase modulator configured as a
time lens is used to uniquely map the pulse shape from the time domain
to the frequency domain, allowing measurement of the pulse shape with
a spectrometer. We discuss the theory of operation and present experi
mental results illustrating 3 ps time resolution.