Study of time — delayed four — wave mixing with Incoherent light for the larger ambipolar diffusion coefficient

ABSTRACT In the paper, we report a theory of measuring the decay time of the dynamic grating and the dephasingtime using time — delayed four — wave mixing with incoherent light for the larger ambipolar diffusion coefficient, and discuss the calculated results.1. INTRODUCTION Recently techniques for the measurement of ultrafast processes in condensed materials have developedrapidly. Pulse with durations of the order of picoseconds and tens of femtoseconds have become available aspowerful tools for ultrafast measurement. However, femtosecond laser devices are still complicated andsophisticated. Even though tunable pulses of durations shorter than I 00 fs over the broad visible region havebeen reported by hybrid mode — locking, it is still inconvenient to perform relaxation experiments using theselight sources since the apparatus required is available only in very few laboratories, moreover it is inconvenientto change from one dye laser to another. Instead of using ultrashort pulses, incoherent light with a shortcoherent time can also achieve a high time resolution, as has been suggested' and verified experimentally by