We describe a new heterodyne nondegenerate pump-probe waveguide measur
ement technique that permits independent control of wavelengths, pulse
widths, and polarizations of the pump and probe pulses in a collinear
geometry. This technique provides both time- and spectral-domain info
rmation and can be applied to transmission and index measurements alik
e. We demonstrate this technique for the measurement of gain dynamics
in a strained-layer single-quantum-well diode laser.